Capacity Implications of Advanced Stop Lines for Cyclists. Transport Research Laboratory, UK. by Guia Buenas Practicas Motocicletas

Capacity implications of Advanced Stop Lines for cyclists Prepared for Charging and Local Transport Division, Department for Transport G T Wall, D G Davies and M Crabtree

TRL Report TRL585

First Published 2003 ISSN 0968-4107 Copyright TRL Limited 2003.

This report has been produced by TRL Limited, under/as part of a contract placed by the Department for Transport. Any views expressed in it are not necessarily those of the Department.

TRL is committed to optimising energy efficiency, reducing waste and promoting recycling and re-use. In support of these environmental goals, this report has been printed on recycled paper, comprising 100% post-consumer waste, manufactured using a TCF (totally chlorine free) process.

CONTENTS Page Executive Summary

1 Introduction

1.1 Overview 1.2 Methodology

3 3

2 Previous research into the use of ASLs

2.1 Previous research in the Netherlands 2.2 Previous research in the UK

4 4

3 Theoretical capacity implications of installing ASLs 3.1 The setting of intergreen timings 3.2 The saturatin flow formulae used in OSCADY 3.3 Limitations of the use of OSCADY in assessing ASLs 3.4 Scenarios of ASLs with a nearside cycle lane 3.5 Scenarios of ASL with a central cycle lane 3.6 Discussion 4 Before and after video surveys â&#x20AC;&#x201C; method 4.1 Site selection 4.2 Dates of the video surveys and questionnaires 4.3 Lane widths 4.4 Parameters measured from video 5 Observed changes in saturation flow

5 5 6 7 10 10 10 10 10 11 11 11 11

5.1 Method for measuring saturation flow 5.2 Measured saturation flow results 5.3 Measured results compared to OSCADY predictions 5.4 Using OSCADY at junctions with ASLs

11 11 12 13

6 Observed changes in motor vehicle and bicycle traffic

6.1 Motor vehicle flows and turning proportions 6.2 Motor vehicles crossing the first stop line 6.3 Motor vehicle/bicycle interactions 6.4 Bicycle flows and turning proportions 6.5 Queuing positions of cyclists 6.6 Cyclist approach lane 6.7 Cyclists going through a red light 7 Questionnaire survey and results

13 14 14 15 15 15 16 16

iii

Page 8 Conclusions and recommendations 8.1 Conclusions 8.2 Recommendations

18 18 18

9 References

10 Acknowledgements

Appendix A: Photographs of the four sites

Appendix B: Drawings of the four sites

Appendix C: ASL questionnaire

Appendix D: ASL questionnaire results

Appendix E: Motor vehicle flow results

Appendix F: OSCADY output files for the Epsom Road / Boxgrove Road junction

Abstract

Related publications

Executive Summary Introduction An Advanced Stop Line (ASL) is a facility that allows cyclists to position themselves at the front of the queuing traffic at a signalised junction stop line. It includes a cycle lane approach (most commonly located on the nearside) to a waiting area approximately 5 metres deep. The idea is to make cyclists more visible to motorists to reduce the risk of conflict and allow them to negotiate the junction more safely. Before now, the effect of ASLs on capacity has not been considered in detail. This is rectified in this project which studied the effect on capacity of Advanced Stop Lines (ASLs) using the signal-controlled junction modelling computer program, OSCADY (Optimised Signal Capacity And Delay) and ‘before’ and ‘after’ video surveys. The research is part of a project on Cycling Facilities and Engineering, commissioned by the Charging and Local Transport Division of the Department for Transport (DfT). Previous research Following the successful schemes in the Netherlands (Kuijper, 1982), ASLs were first installed in the UK in Oxford in 1984. Results showed that ASLs operated satisfactory and were generally understood by road users (Wheeler, 1992 and 1993). The ‘original’ layout was replaced in the early 1990s by a ‘simplified’ layout that required no additional signal head at the motorists’ stop line (Wheeler, 1993). Further research was carried out into the benefits of a non-nearside approach cycle lane where turning proportions suited (Wheeler, 1995). Following the research, some guidelines were listed for the installation of ASLs in TAL 8/93. Previous research was reviewed to see whether sufficient time is given for cyclists to safely clear the junction and whether intergreen timings or minimum green times need to be altered after the installation of an ASL (Federal Highway Administration, 1988). Capacity implications of installing ASLs It is possible to predict (approximately) the saturation flow for traffic signal controlled stop lines from work carried out by Kimber (Kimber et al., 1986). The formulae derived by Kimber use geometric parameters such as lane width, whether the lane is nearside or not, and turning radii etc to predict saturation flow for a given stop line. A ‘standard’ lane is defined by Kimber as a lane of 3.25 meters width, non-nearside, flat, straight with no turning traffic: a standard lane has a predicted saturation flow of 2,080 passenger car units/hour (pcu/hour). When considering ASLs there are two key geometric features, which affect saturation flow: l

Nearside lane: saturation flow is reduced by 140 pcu/hour compared with a non-nearside lane.

Lane width: for each additional metre of lane width the saturation flow increases by 100 pcu/hour (and decreases by the same amount for every metre reduction down to a practical limit of about 2m).

In order to assess the capacity implications of installing ASLs, five different theoretical ‘before’ and ‘after’ scenarios were examined. These scenarios were used to predict the effect on capacity of installing an ASL with either a nearside or a central cycle lane. For junctions with ASLs with nearside cycle lanes, a small increase in saturation flow was predicted, given that the new nearside lane can be considered as non-nearside because there is now some space between it and the kerb. The increase occurs because the change from nearside to non-nearside more than offsets the reduction due to the reduction in lane width caused by the installation of the cycle lane (although the differences are modest). For junctions with ASLs with a central cycle lane, a reduction in saturation flow would be expected because, as before, the nearside lane is reduced in width, but, this time, it remains next to the kerb. Video surveys and questionnaire The ‘before’ and ‘after’ video surveys were carried out at four sites in Guildford, Surrey. Two sites were located at the same T-junction (Epsom Road/Boxgrove Road), with the other two sites located at crossroads (London Road/York Road and Epsom Road/A247). All sites had a nearside cycle lane; Epsom Road/Boxgrove Road westbound also had a central cycle lane. Two sites had a traffic lane removed (Epsom Road/Boxgrove Road eastbound and westbound) whereas the other two sites did not. The questionnaire survey showed that the newly installed ASLs had a favourable response from the majority of cyclists: they were thought to be safer and easier to use as cyclists were allocated more road space, were more visible to drivers and could turn right much more easily. The main concern expressed was that, some drivers did not comply with the new layout, driving into the cycle lane and stopping inside the ASL. Results and conclusions From the saturation flow formulae and the video surveys, the capacity implications of installing ASLs were assessed. Three possible sources were examined to see if they resulted in a loss of capacity. They were: 1 Moving the drivers’ stop line back 5 metres. 2 The reduced width or removal of traffic lane(s). 3 The different queuing/positioning behaviour of cyclists. Generally speaking, when considering individual intergreen times at a junction (without pedestrian facilities) moving one or more of the stop lines back by five metres will either require no change or an additional one second. It is important to consider each junction separately, taking into account the fact that cyclists will take longer than motorised traffic to clear past conflict points. In some circumstances this may mean that a longer intergreen or a longer minimum green time is desirable. The intergreen timings at the four sites used in the video surveys were unchanged. 1

There are implications for installing ASLs concerning the positioning of, and green extension times from, vehicle detectors used in signal control. These were not considered in this project. At the two sites where the number of traffic lanes remained the same (London Road/York Road and the Epsom Road/A247), there was a slight (but not statistically significant) increase in saturation flow of 1.5% and 5.5% respectively. At the two sites where a traffic lane was removed (Epsom Road/Boxgrove Road eastbound and westbound) there were, as would be expected, large reductions in saturation flow of 47% and 38% respectively. With a nearside cycle lane, given the assumption that the new nearside traffic lane can be defined as non-nearside for the purposes of saturation flow prediction, the predicted changes in saturation flow for nearside lanes were similar to those measured. For offside lanes, there was a difference between the measured and predicted saturation flows. However, saturation flows of the offside lanes at Epsom Road/A247 and Epsom Road/Boxgrove Road westbound were affected by the presence of a row of cones and a central cycle lane respectively. Cyclist and vehicle behaviour was recorded at each junction together with vehicle flows and turning proportions (peak and off-peak) number of vehicles stopping inside the ASL, vehicle/cycle interactions, cycle flows and turning proportions, cyclist queuing position, cyclist approach lane and the number of cyclists going through a red light. There was no evidence from video that cyclist queuing/positioning behaviour had any noticeable effect on capacity (although the bicycle flows at the four sites were small). Recommendations Recommendations from the study were as follows: l

The checking and possible extension of the intergreen and/or minimum green times, particularly at large signal-controlled junctions and where cyclists are observed to cross the stop line near the end of green, to ensure that cyclists are given adequate clearance time.

Consideration given to the positioning of, and extension times for, vehicle detectors used in the control of traffic signals. Use of signal controlled junction modelling computer programs such as OSCADY to assess the impact of changes, especially where a traffic lane is to be removed. Further encourage the compliance of motorised vehicle drivers with ASLs by the use of, for example, signs, education and/or enforcement, and maintaining the visibility of road markings.

Further research to be carried out to establish the safety record of ASLs and establish more precisely the safety and capacity relationships.

References Kimber R M, McDonald M and Hounsell N B (1986). The prediction of saturation flows for road junctions controlled by traffic signals. Research Report RR67. Crowthorne: TRL Limited. 2

Wheeler A H (1992). Advanced stop lines for cyclists at Oxford, Newark and Bristol. Research Report RR336. Crowthorne: TRL Limited. Wheeler A H, Leicester M A A and Underwood G (1993). Advanced stop lines for cyclists. Traffic Engineering and Control. 34(2) pp 54-60. Wheeler A H (1995). Advanced stop lines for cyclists - A simplified layout. Traffic Engineering and Control. 36(5) pp 283-289.

1 Introduction 1.1 Overview The purpose of the project report on here was to assess the capacity implications of installing Advanced Stop Lines for cyclists (ASLs). This research is part of a project on Cycling Facilities and Engineering, commissioned by the Charging and Local Transport Division of the Department for Transport (DfT). An Advanced Stop Line is a facility that allows cyclists to position themselves ahead of queuing motor vehicles at signalised junctions. It must include a cycle lane approach (most commonly located on the nearside of the road, but need not actually be part of the road) to a waiting area approximately 5 metres deep. Its function is to aid cyclists through the junction effectively and safely by enabling them to move off ahead of motor vehicles and clear the junction first. This makes cyclists more visible to motorists and can reduce the risk of conflict, especially with turning vehicles. Figure 1 shows the typical layout of two types of ASLs. ASLs are recommended by the DfT, the Institution of Highways & Transportation (Transport and the Urban Environment, 1997) and other organisations as a means of assisting and encouraging cyclists. They have been introduced extensively in a number of UK towns. Their effects on traffic capacity, however, have never been researched in detail in the UK. This report starts, in Chapter 2, by reviewing previous research into ASLs in the Netherlands and the UK. The remaining chapters are structured as follows. Chapter 3 assesses the theoretical capacity implications of installing ASLs with a nearside and a central cycle lane. This involves looking at the setting of intergreen timings and examining the saturation flow formulae originally derived by Kimber et al. (1986) and used in OSCADY (Optimised

ASL with a nearside cycle lane

Signal Capacity And Delay). Chapters 4-6 describe the ‘before’ and ‘after’ video surveys; the site selection, the method and the results. Chapter 7 presents the results of the questionnaires and Chapter 8 discusses the conclusions and recommendations from the study. 1.2 Methodology Where a traffic lane is removed to provide an ASL, it is undoubtedly true that capacity will be reduced. With most ASL schemes, however, the approach cycle lane is often provided for by reducing the width of the traffic lane(s) and no traffic lane is lost. The effects of such schemes need to be assessed in order to help traffic engineers decide on where and how their use is feasible. It is possible that a loss of capacity could arise from 3 sources. These are: 1 Moving the drivers’ stop line back 5 metres - an increase in the intergreen timings (or lost time) may be required for safe operation at certain junctions. Also, on flared approaches1 , the capacity of the flare would be reduced (by approximately 1 pcu per bay per traffic cycle). This would have, however, little effect on capacity, except where the flare is very short and/or where the flared lanes receive frequent short greens. 2 The reduced width or removal of traffic lane(s) – cycle lanes are often provided for by reducing the width of the traffic lane(s). In some circumstances, a traffic lane may be removed. 3 The different queuing/positioning behaviour of cyclists – some vehicles may be delayed when the signals change

A flared approach is an approach which flares (or widens) out towards the drivers’ stop line to provide an extra storage bay or bays. A bay is a short lane providing extra capacity at the vehicle stop-line.

ASL with a central cycle lane

NB A nearside cycle lane can be mandatory (solid line) or advisory (broken line); but a central cycle lane must be advisory so motor vehicles can cross it if necessary

Figue 1 Two types of Advanced Stop Lines

to green due to the time taken for cyclists, waiting in the reservoir, to clear the junction, leading to extra start-up lost time. These effects are investigated individually and in combination in this report.

2 Previous research into the use of ASLs 2.1 Previous research in the Netherlands In 1978, the City of Leiden (in the Netherlands) introduced ASLs for cyclists at four sites (Kuijper, 1982). It was used as an experiment commissioned by the Directorate of Traffic of Leiden, as well as being independently suggested by the Leiden Cyclists Association. It became apparent that ASLs could make a contribution to the flow of traffic as well as reducing the number of conflict situations between vehicles and cyclists. Drivers in the Netherlands (driving on the right) when turning right must give way cyclists on their nearside (or right) who are going straight-ahead. These conflicts are removed with the installation of an ASL. From the four trial sites, the advanced stop line was seen as a low cost traffic provision that presents advantages to both cyclists and car drivers. Further ASLs were introduced in several Dutch towns including Enschede (Heys and Vredeveld 1983; Salomons 1985) with some variations in design, but comprising a nearside cycle lane with a waiting area (or reservoir) for cyclists marked with a painted cycle symbol ahead of the motorists’ stop line. At the Enschede sites, the word FIETSERS (CYCLISTS) was painted in the reservoir to reduce motorists stopping in this area, and to encourage cyclists to use it. At one site, a red coloured surface was installed on the cycle lane to emphasise it further. However, two legal imperfections were found later. Firstly, there was no legal requirement about which stop line motorists should obey and secondly, it was unclear whether cyclists had priority over motorists in the reservoir area when the signals were green. Difficulties may have arisen if an accident had taken place. Studies carried out at the schemes in Leiden (Kuijper 1982) and Enschede (Salomons 1985) showed that the majority of motorists and cyclists understood and complied with the new layout. Centre for Research and Contract Standardisation in Civil Engineerng (CROW, 1993) have produced a technical design manual offering road designers advice on cycling infrastructure in the Netherlands. With reference to ASLs, it recommended one cycle approach lane per traffic lane. 2.2 Previous research in the UK Following the successful schemes in the Netherlands, ASLs were first introduced to the UK in Oxford in August 1984 on Parks Road at the signalised junction with Broad Street, Catte Street and Holywell Street (Department of Transport 1986a). These were followed by schemes in Newark (Department of Transport 1989) and Bristol (Department of Transport 1991). These schemes were studied by the Transport Research Laboratory (Wheeler 1992; Wheeler et al. 1993) as work 4

commissioned by the then Traffic Policy Division (now Charging and Local Transport Division) of the then Department of Transport (now Department for Transport). The results showed that ASLs operated satisfactory and were generally understood by road users. At each site, over 75% of cyclists made proper use of the cycle lane and reservoir and over 90% of motorists kept out of the cycle lane. Overall, 82% of motorists arriving whilst the traffic signals were red kept out of the reservoir. A further four schemes in Bristol, Cambridge and Manchester had a ‘simplified’ layout based on the Dutch design (Wheeler 1995). With the earlier schemes, there was an additional signal head installed at the motorists’ stop line, a mandatory cycle lane and comprehensive signing. This additional signal head carried a green cycle symbol allowing cyclists into the reservoir between the two stop lines. The ‘simplified’ layout, outlined in Traffic Advisory Leaflet 8/93 (Department of Transport 1993), involved no modifications to the signal arrangements (i.e. no additional signal head at the motorists’ stop line). It can have an advisory rather than mandatory cycle lane and normally only signing to Diagrams 958.1, 959.1 or 967 of the Traffic Signs Regulations and General Directions 1994 (SI 1994/1519). This new layout was developed by former Avon County Council and is considerably cheaper to install. This ‘simplified’ layout is now the norm. The use of an additional signal head in the ‘original’ layout requires DfT authorisation that is given only in exceptional circumstances. Results from the later surveys (Wheeler 1992) showed that the cycle lanes and ‘simplified’ ASLs were used satisfactorily by most cyclists, in similar proportions to the earlier study. It seemed probable that the simplified layout, with the combination of a mandatory cycle lane and a strongly coloured road surface in the cycle lane and reservoir, is most effective at improving motorists’ compliance with road markings. The average proportion of cyclists inconvenienced by motorists was 9%, with encroachment of the reservoir by motorists when arriving at the stop line on red averaging 33%. Wheeler (1995) also suggested that a central cycle lane between left-turn and ahead all-vehicles lanes to be worth consideration, particularly for junction arms with a large left-turning flow of motor vehicles and a large flow of cyclists going straight ahead. Following on from Wheeler’s study (1995), research has been carried out to investigate the value of a non nearside approach lane and assess the effect of different signal timings on the usefulness of an ASL (Ryley 1996). Six sites were chosen; three with a nearside cycle approach lane (2 at Portsmouth and 1 at Cambridge) and three with a non-nearside approach lane (Manchester, Chelmsford and Bristol). It was found that a large proportion of cyclists used a nearside cycle lane approach to turn left or continue ahead. Few cyclists used the complete length of the nearside cycle lane up to the stop line to turn right. The majority of right-turning cyclists used either part or none of the cycle lane. It was found that a central cycle lane performed the function of putting cyclists to the right of vehicles in an all-vehicle lane,

usually a left-turning lane, with no visible safety problems for cyclists entering it. Signal timings are generally determined by vehicle flow at the different arms of the junction. This affects both the length of the green time and the cycle time (i.e. the time it takes to cycle around all phases/stages at a junction). Cyclists can only make full advantage of the ASL when they can pass vehicles and reach the head of the queue, i.e. when signals are red. When the signals are green, potential conflicts can occur between left turning vehicles and straight-ahead cyclists using the nearside cycle lane (or in the case of a middle cycle lane, right-turn cyclists and straight-ahead vehicles in the offside traffic lane). Longer greens may, therefore, give greater opportunity for these events occur. However, no strong relationship between signal timings and the number of conflicting movements of cyclists and vehicles was found. Using results from Ryley’s study and previous research, some guidelines were listed for the installation of ASLs. They included: l Using the new simplified layout which does not have a second signal head at the motorist stop line (Wheeler 1995). It has proven to be as safe as the original layout but cheaper to install. l Using a different surface colouring (possibly made of an anti-skid material) from the rest of the carriageway for the cycle lane and reservoir, with the cycle logo included in the reservoir. The cycle lane should be at least 1.5 metres wide. l Using a non nearside cycle lane if there is more than one all-vehicle lane and a large proportion of traffic turning left. This is especially appropriate where a filter lane is provided and there is a large number of ‘ahead’ cyclists.

Removing obstructions in the cycle lane such as parked cars by greater enforcement.

There have been no published studies to date showing how the number and type of accidents have been affected by the installation of ASLs.

3 Theoretical capacity implications of installing ASLs There are 3 possible sources of capacity effects from installing ASLs. These are: 1 Moving back the drivers’ stop line (5 metres). 2 Reduced width/removal of traffic lane(s). 3 Different queuing/positioning behaviour of cyclists. 3.1 The setting of intergreen timings The intergreen (or clearance) time is the period of time between the end of green on one phase and the start of green on another phase. They are set in relation to vehicular conflict points at the junction. In TA 16/81 (Department of Transport 1981), there are general principles of how to set intergreen timings. The timings are for mixed traffic, which include cyclists. Figure 2 shows the location of the potential collision points at the junction. The advice given in TA 16/81 is as follows: When east-west arms are losing the right of way, then the distance ‘x’ = the greater of AF-BF or CH-DH. When north-south arms are losing the right of way, then the distance ‘x’ = the greater of DE-AE or BG-CG.

Potential collision points

E C

Figure 2 Determination of intergreen times

Tables 1 and 2 show what intergreen times are recommended for different distances ‘x’, for ahead and turning traffic.

Table 1 Intergreen times for straight-ahead traffic

In 1995, the Palo Alto (California) Transportation Division timed 689 cyclists at six intersections where clearance time accidents had occurred or were considered likely to occur, based on physical characteristics and cycle flows. The majority of the cyclists were high school and college students and adults, as well as a few primary school students. The speed of cyclists who continue without stopping or who start from standstill ranged from 4.0m/s (for small children) to 7.3m/s (for fit adults). From Tables 1 and 2, the intergreen time increases by 1 second for approximately every 9 metre and 6 metre increase in the distance ‘x’ for ahead and turning traffic respectively, once the distance ‘x’ increases above 9 metres. However, for the distances ‘x’ given in both tables, ahead traffic and turning traffic is assumed to travel at an average speed of up to 5.8m/s and 4m/s respectively whilst clearing the junction. Therefore, assuming only a small proportion of the amber is used as effective green time, the intergreens recommended in TA 16/81 provide enough time for the cyclists in this sample. A Danish study was carried out to measure the effects of recessed stop lines in vehicle lanes (Road Directorate: Denmark Ministry of Transport 1994). Normally, the stop line is moved back by 5 metres relative to the cyclists’ stop line. Potential vehicle/cycle conflicts can occur between right turning vehicles and straight-ahead cyclists. The underlying idea was to improve the visibility of cyclists, especially to vehicles turning right at the junction at the beginning of the green period. It concluded that the recessing of vehicle stop lines increases the safety of cyclists at junctions controlled by traffic lights, where there are extended cycle paths. It was also concluded that moving the stop line back will not normally incur any extension of the intergreen period as its duration is mainly determined by pedestrians and cyclists as they take longer to clear the junction. The experience of those Local Authorities (such as Avon County Council/Bristol City Council, Hampshire County Council, Nottinghamshire County Council, Surrey County Council and City of York Council) that have introduced ASLs, is that capacity has not been significantly affected and no significant changes to signal retiming has been required. This suggests that moving back the drivers’ stop line would not normally have any significant effect on capacity (thus the first possible source of a loss in capacity assessed).

Distance ‘x’ (metres) 9 10-18 19-27 28-36 37-46 47-54 55-64 65-74 Intergreen (secs)

Table 2 Intergreen times for turning traffic Distance ‘x’ (metres) 9 10-13 14-20 21-27 28-34 35-40 41-45 46-50 Intergreen (secs)

With the installation of an ASL, comprising of a cycle lane and a 5-metre reservoir, the vehicle stop line would normally be moved back 5 metres. Vehicles would, therefore, travel an extra 5 metres in order to clear the junction. From Tables 1 and 2, this normally equates to either no additional intergreen, or an additional one second, depending on whether adding 5 metres takes you into the next column in the table or not. For turning traffic, an extra 2 seconds may be strictly necessary if ‘x’ was originally 9 metres before moving the stop line. If ASLs are installed on all approaches, the value of ‘x’ will often remain the same, so the intergreen time need not be changed (unless there are other considerations, including pedestrian facilities). For more complicated situations, a series of one-second intergreen adjustments may accumulate and have a significant impact on junction lost time. The Manual on Uniform Traffic Control Devices (U.S.A Federal Highway Administration 1988) says that ‘bicycles generally can cross intersections under the same signal timing arrangements as motor vehicles. Where bicycle use is expected, extremely short change intervals should not be used and an all-red clearance interval may be necessary’. Two distinct cases need to be considered when setting phase times and intergreen times that are suitable for cyclists. These are: 1 where a cyclist enters the junction at the end of the green or during the amber phase – the time it takes for such cyclists to clear the conflict points needs to be considered; and 2 where a cyclist, having stopped at a red signal, starts from a new green signal – normal minimum greens may not be long enough for a cyclist to clear conflict points. It has been suggested from a study in the U.S.A (Wachtel et al. 1995) that there is a need for clearance times to be adjusted, particularly where cyclists are given insufficient time to clear the junction. Signalised junctions that will particularly benefit as a result of adjusting the clearance times will be those with: l

A history of vehicle/cycle accidents where there was an obvious clearance time problem.

A wide multilane major road with a significant flow of cyclists.

A cycle lane or marked cycle route crossing the junction. Significant gradients on one or more of the approaches.

3.2 The saturatin flow formulae used in OSCADY OSCADY (Optimised Signal Capacity And Delay) is a computer program for calculating capacities, queue lengths and delays (both queuing and geometric) for isolated, traffic signal controlled, junctions (Binning 1998). The junctions that can be modelled are three-arm ‘T’ junctions, crossroads and staggered crossroads. OSCADY is specifically designed to model isolated (uncoordinated) signalised junctions. Saturation flow is the rate of flow across a stop line while there is a queue remaining. At existing sites that are sufficiently loaded with traffic, the saturation flows can be

measured directly. However, when planning a new junction or major alterations, the saturation flows have to be predicted. Now, Kimber et al. (1986) described a comprehensive programme of measurement of saturation flow at traffic signals and the predictive formulae derived empirically from those measurements. These formulae have been incorporated into OSCADY, hence OSCADY can be used to predict the performance of a proposed signal controlled junction. The effects of traffic composition are normally represented by passenger car units (pcus). The following values were derived. Medium commercial vehicle Heavy commercial vehicle Bus / Coach Car Motorcycle Bicycle

1.5 pcu 2.3 pcu 2.0 pcu 1.0 pcu 0.4 pcu 0.2 pcu

The empirical saturation-flow formulae for unopposed traffic used in OSCADY show that for lanes containing straight-ahead traffic: a Saturation flow is 2080 pcu/hr for a flat-or-downhill, non-nearside lane of ‘average’ width 3.25 metres. b Saturation flow is reduced by 140 pcu/hr for a nearside lane. c Saturation flow increases/decreases by 100 pcu/hr with each added/subtracted metre of width. The allowed range is 2 metres to 10 metres. d Saturation flow is reduced by 42 pcu/hr or 2% for every 1% increase in uphill gradient. Downhill gradients have no effect on saturation flow. e Saturation flow is not affected by exit width, provided it is greater than or equal to entry width. However, when

'Before' 1 straight ahead lane

the straight-ahead exit width is less than the entry width, the saturation flow is reduced by 50 pcu/hr per metre, although this change only applies when differences are minor: it does not account for a reduction of the number of lanes or funnelling where the reduction in saturation flow is likely to be more drastic. In addition, saturation flow is affected by the proportions of turning traffic and the radii of turn. This reduction in capacity for the vehicle lanes could, however, be compensated for by the increase in capacity of the cycle lane, but only when the proportion of cyclists is high. 3.3 Limitations of the use of OSCADY in assessing ASLs In order to assess the capacity implications of installing ASLs, five different theoretical ‘before’ and ‘after’ scenarios were examined. These scenarios were used to assess the effect on capacity of installing an ASL with either a nearside or a central cycle lane which. The width of the cycle lane was assumed to be 1.2 metres as this is thought to be more typical than the 1.5 metres recommended by DfT. This width was subtracted from the other lane or lanes on that approach. As the saturation flow of a lane decreases for every metre reduction (down to 2 metres), the installation of an ASL is predicted to reduce the capacity of the approach. The first three scenarios were used to assess the effect of installing a nearside cycle lane with an approach of 1, 2 or 3 straight-ahead lanes respectively. The final two scenarios assessed the effect of installing a central cycle lane with a left turning lane and 1 or 2 straight-ahead lanes. The results for the various scenarios (shown in Figures 3-7) are taken from Kimber’s saturation flow formulae. These formulae, however, may be very slightly in error when considering ASLs as discussed in Section 3.6.

'After' 1 straight ahead lane and a 1.2m nearside cycle lane (taken from lane 1)

+20 pcu/hr non nearside assumption -120 pcu/hr nearside assumption

Figure 3 Installing and ASL with a nearside cycle lane next to a straight ahead lane 7

'Before' 2 straight ahead lanes

'After' 2 straight ahead lanes and a 1.2m nearside cycle lane (taken equally from both lanes)

+80

-60

+20 pcu/hr non nearside assumption -120 pcu/hr nearside assumption

Figure 4 Installing and ASL with a nearside cycle lane with 2 straight-ahead lanes

'Before' 3 straight ahead lanes

'After' 3 straight ahead lanes and a 1.2m nearside cycle lane (taken equally from all 3 lanes)

+100

-40

+20 pcu/hr non nearside assumption -120 pcu/hr nearside assumption

Figure 5 Installing and ASL with a nearside cycle lane next to 3 straight-ahead lanes

'Before' 1 left turning lane and 1 straight ahead lane

'After' 1 left turning lane, 1 straight ahead lane and a 1.2m nearside cycle lane (taken equally from both lanes)

-55

-60

-115 pcu/hr

Figure 6 Installing an ASL with a central cycle lane between a left-turning lane and a straight-ahead lane

'Before' 1 left turning lane and 2 straight ahead lanes

'After' 1 left turning lane, 2 straight ahead lanes and a 1.2m nearside cycle lane (taken equally from all 3 lanes)

-36

-40

-116 pcu/hr

Figure 7 Installing and ASL with a central cycle lane between a left-turning lane and 2 straight-ahead lanes

Other factors not accounted for in the scenarios include: Vehicles that sometimes encroach into a cycle lane, particularly when the vehicle lane is narrow or when there are few cyclists. This will increase the effective vehicle lane width and so alter the saturation flow. Cyclists (particularly groups of cyclists) that wait in the reservoir causing vehicles to be delayed when the signals change to green due to the time taken for them to clear the junction. However, cyclists would probably have been at the front of the traffic queue or randomly distributed in the traffic queue prior to the installation of the ASL, so this may make no difference in practice.

3.4 Scenarios of ASLs with a nearside cycle lane Figures 3-5 show the predicted effect on saturation flow of installing a 1.2 metre wide cycle lane with 1, 2 or 3 straight-ahead lanes. The results for all three scenarios were the same, i.e. an increase in saturation flow in the ‘after’ situation of 20 pcu/hr. This is due to lane 1 being treated as a non-nearside lane, increasing its capacity by 140 pcu/hr. However, a reduction in lane width of 1.2 metres for the installation of the cycle lane (spread over 1, 2 or 3 lanes) leads to a reduction in saturation flow of 120 pcu/hr. Therefore, overall, there is an increase of 20 pcu/hr (as shown in Figures 3-5). This increase does not take into account the use of the cycle lane. If lane 1 is assumed to remain ‘nearside’, there is a reduction in capacity of 120pcu/ hr for all three scenarios. In practice, the change in saturation flow will probably be between (–120 pcu/hr) and (+20 pcu/hr + 0.2 * hourly cycle flow). However, this would require a cycle flow of over 600/hr to ensure an increase in saturation flow, which is highly unlikely in the UK. Turning traffic has not been included in the assessment for reasons of clarity: the effect is non-linear, is independent of other geometric factors (eg lane width) and is sensitive to the turning radius 3.5 Scenarios of ASL with a central cycle lane Figure 6 shows the effect of installing a 1.2-metre wide central cycle lane between a left turning and straight-ahead lane. Figure 7 differs from Figure 6 in that it has the central cycle lane positioned between a left turning lane and two straight-ahead lanes. It was assumed that the left turning radius was 15 metres. The capacity of a leftturning lane, unlike a straight-ahead lane, reduces to a lesser extent and in a slightly non-linear way as the lane width reduces. Central cycle lanes do not affect the nearside nature of the inside lane (this may not be true of nearside cycle lanes). The results for Figures 4 and 5 show

a similar reduction in capacity (115pcu/hr and 116 pcu/hr respectively). This excludes the use of the cycle lane. Again, for reasons of clarity, dedicated lane usage has been assumed (ie the nearside lane containing 100% left turners, the offside lane 100% straight-ahead traffic). 3.6 Discussion It is not clear whether and to what extent the lane nearest the kerb, but with a cycle lane intervening, should be treated as ‘nearside’. It has been shown empirically in the research which underpins OSCADY (Kimber et al. 1986) that a nearside lane has a lower capacity, but the underlying reasons for this can only be surmised e.g. left-turning traffic and being nearer to the kerb, pedestrians and cyclists. OSCADY treats such lanes as nearside automatically thus possibly giving a slightly pessimistic saturation flow value. Given that the difference in saturation flow value between a nearside lane with and without a cycle lane is not known, a pessimistic value is more appropriate under the circumstances than being potentially optimistic. The biggest effects predicted here are actually quite small (of the order of 2pcu/min). ‘Before’ and ‘after’ video surveys have been carried out (see Section 6) to confirm the validity of these results. The theoretical effects were then assessed against the observed effects at 4 sites in Guildford.

4 Before and after video surveys – method 4.1 Site selection In order to measure the capacity affects of installing ASLs, ‘before’ and ‘after’ video surveys were carried out at four sites in Guildford, Surrey. The sites were selected following consultation with a number of local authorities. ASLs with no cycle lanes were not considered as suitable sites, as they are not good practice and in the new Traffic Signs Regulations and General Directions will not be permitted. Table 3 shows the locations of the four sites with their respective characteristics. The sites selected had a range of characteristics in terms of their junction type, type of cycle lane installed and whether a traffic lane had to be removed or not. Two sites were located at the same T-junction (Epsom Road/Boxgrove Road2 ) with the other two sites located at crossroads. All sites had a nearside cycle lane with

The Epsom Road/Boxgrove Road junction contains an entrance/exit to a Ministry of Agriculture, Food and Fisheries office. The vehicle flows entering and leaving this arm of the junction were very small and have therefore been ignored.

Table 3 ASL sites selected Type of cycle lane installed

Has an approach lane been removed

Site

Type of junction

London Road / York Road, Guildford

Cross-roads

London Road eastbound

Nearside

Epsom Road / A247, Guildford

Cross-roads

Epsom Road eastbound

Nearside

Epsom Road / Boxgrove Road, Guildford

T-junction

Epsom Road eastbound

Nearside

Yes

Epsom Road / Boxgrove Road, Guildford

T-junction

Epsom Road westbound

Nearside and Central

Yes

ASL on which approach

Number of lanes on approach

the exception of Epsom Road/Boxgrove Road westbound which had a nearside and a central cycle lane. Two sites had a traffic lane removed whereas the other two sites did not. All of the junctions chosen had large vehicle flows but low cycle flows. However, this was not a problem for this research as it was the impact of the ASL, rather than the flow of cyclists, that was at issue.

Table 5 Lane widths (metres) in the ‘before’ and ‘after’ survey ‘After’ Cycle lane (near side)

London Road / York Road 4.0 n/a n/a Epsom Road / A247 3.6 3.7

‘Before’

Lane 1

Cycle lane (central)

Lane 2

1.1

2.9

n/a

1.3

3.0

n/a

3.0

Epsom Road / Boxgrove Road (eastbound)* 3.0 2.8 n/a 1.5 3.6

n/a

Epsom Road / Boxgrove Road (westbound) 2.7 3.0 2.9 1.5

1.6

2.8

Lane 1

4.2 Dates of the video surveys and questionnaires Table 4 shows the dates of the ‘before’ video survey, the installation of the ASL, the ‘after’ video survey and the questionnaires. After the installation of the ASL, a gap of at least a month was left before the ‘after’ survey was carried out in order for road users to become familiar with the new layout. The ‘before’ and ‘after’ video surveys involved four hours of recording from 07:00 – 11:00, using one video camera on the required approach to the junction. The questionnaires involved interviewing as many cyclists as possible at the junction during the same four-hour period. 4.3 Lane widths Table 5 shows the lane widths (in metres) of the various traffic and cycle lanes during the ‘before’ and ‘after’ surveys. At the Epsom Road/Boxgrove Road eastbound site, lane 1 in the ‘after’ survey had a new white ghost island marking to indicate the right-hand extreme of this lane (rather than the traffic island). This had the effect of narrowing the available road width by 0.7m. 4.4 Parameters measured from video The videos for both sets of surveys at each of the four sites were analysed in order to assess the capacity implications of installing ASLs. As well as measuring saturation flow, the videos were also used to obtain data relating to cyclist and vehicle behaviour at the junction. At each site, measurements were made and data recorded relating to: l Vehicle flows and proportions (peak and off-peak). l Number of motor vehicles and cyclists stopping inside ASL. l Vehicle/cycle interactions. l Cycle flows and proportions. l Cyclist queuing position. l Cyclist approach lane. l Numbers of cyclists going through a red light (The number of motorists going through a red light was not measured as it was thought that there would not be enough instances of this behaviour to be able to suggest general trends).

Lane 2

Lane 3

n/a

2.7

* ‘After’ reduced by 0.7m due to wider central ghost island.

5 Observed changes in saturation flow 5.1 Method for measuring saturation flow Saturation flow is defined to be the maximum rate of discharge from a queue. Saturation flows were measured from video for each lane on the approach. The measurements were made in pcus (passenger car units) over 25 signal cycles from 08:00. Goods vehicles with at least 6 wheels were assigned a value of 2 pcu (a simplification that is easily tolerated since such vehicles made up less than 1% of the flow at each site), and all other motor vehicles a value of 1 pcu. Bicycles were assigned a value of 0.2 pcu. Each of the 25 signal cycles measured contained a queue of at least 5 pcus. The saturation flow measurements for the ‘before’ and ‘after’ surveys were based on similar average green times and platoon sizes, enabling an accurate comparison to be made. To allow saturation flow to develop, a suitable interval of 1.5 seconds was given between the start of green and the first vehicle to be counted. This corresponds closely to the default value used for the start displacement in OSCADY (1.4 seconds). This start displacement accounts for the start displacement between the signals changing to green and vehicles getting up to speed. 5.2 Measured saturation flow results Saturation flow measurements based on a relatively small amount of data will vary randomly around the real value.

Table 4 Dates of the ‘before’ and ‘after’ video surveys along with the ASL installation Site

‘Before’ video survey

Installation of ASL

‘After’ video survey

Questionnaire

London Road / York Road

March 1999

July 1999

October 1999

November 1999

Epsom Road / A247

June 1999

July 1999

October 1999

Epsom Road / Boxgrove Road (eastbound)

March 1999

November 1999

March 2000

Epsom Road / Boxgrove Road (westbound)

June 1999

November 1999

March 2000

* Due to the very low cycle flows at this site, a questionnaire was thought to be not worthwhile.

They also vary according to the driving conditions (e.g. rain and darkness). The ‘before’ and ‘after’ video surveys were carried out in reasonably similar conditions in order to minimise differences in saturation flow due to these factors. Small differences in saturation flow between the ‘before’ and ‘after’ survey could be accounted for by either random variations, differences in driving conditions or the small degree of error in the measurements. Table 6 show the saturation flow results (pcu/hr) during the ‘before’ and ‘after’ video surveys for each site. It also shows, where applicable, the percentage change in saturation flow for each lane separately and the approach as a whole from the ‘before’ survey to the ‘after’ survey. The saturation flow results do not take into account usage of the cycle lanes in the ‘after’ surveys. Table 6 Saturation flow results in the ‘before’ and ‘after’ video surveys Lane 1

Lane 2

Lane 3

Total

London Road / York Road 1872 n/a n/a 1872

Epsom Road / A247 2414 2559 n/a

Lane 1

1900 (+1.5%)

Lane 2

Lane 3

5.3 Measured results compared to OSCADY predictions It was predicted that (as discussed in Section 4) saturation flow would be increased by 140 pcu/hr for nearside lanes. These can, as a result of the introduction of a nearside cycle lane, be considered as non-nearside and, increased/ reduced by 100 pcu/hr for every metre increase/reduction in lane width. Table 7 compares the predicted changes with the actual measured changes in saturation flow between the ‘before’ and the ‘after’ survey. In all cases, it has been assumed that the installation of a nearside cycle lane allows the nearside traffic lane to be defined as nonnearside due to the absence of kerbing.

Total

n/a

1900 (+1.5%)

2508 2737 (+3.9%) (+7.0%)

n/a

5245 (+5.5%)

n/a

2490 (-47%)

Table 7 Actual (and predicted) changes in saturation flow (pcu/hr) from the ‘before’ survey to the ‘after’ survey’ Lane 1

4973

Epsom Road / Boxgrove Road (eastbound) 2297 2409 n/a 4706 2490 (+8.4%)

n/a**

Epsom Road / Boxgrove Road (westbound) 2305 2541* 2432 7278 2256 (-2.1%)

n/a**

2278 (-6.3%)

4534 (-38%)

This figure is based on measurements from only 5 signal cycles as the lane was rarely saturated. ** These lanes have been removed as a result of the new layout.

Statistical tests were carried out to see if any of the changes in saturation flow in each lane were significant at the 95% confidence level. All the changes in saturation flow were not significant with the exception of lane 1 at the Epsom Road/Boxgrove Road eastbound approach (see below for an explanation). At the two sites where the number of traffic lanes remained the same (London Road/York Road and the Epsom Road/A247) there was a slight increase in saturation flow of 1.5% and 5.5% respectively. At the Epsom Road/A247 site, there was a 7% increase in saturation flow in lane 2 from the ‘before’ survey to the ‘after’ survey. However, in the ‘before’ survey, there was a row of cones on the right-hand side of lane 2 effectively reducing its lane width by up to 1 metre (reducing its saturation flow by about 100 pcu/hr). Taking this into account, the increase in saturation flow for lane 2 would only be about 3%, reducing the overall increase for the A247/Epsom Road site from 5.5% to 3.4%. These changes in saturation flow at these two sites are not significant and may be accounted for by factors other than the installation of the ASL. 12

At the two sites where the number of traffic lanes remained the same (Epsom Road/Boxgrove Road eastbound and westbound) there was, as expected, a large reduction in saturation flow of 47% and 38% respectively. This was, however, mainly due to the removal of a traffic lane rather than the installation of the ASL.

Predicted change in saturation flow

Lane 2 Actual change in saturation flow

Predicted change in saturation flow

Actual change in saturation flow

London Road / York Road +30 +28

n/a

Epsom Road / A247 +80 +94

+30*

+78*

Epsom Road / Boxgrove Road (eastbound) +200 +193 n/a

n/a

Epsom Road / Boxgrove Road (westbound) +140 -49 -10

-154**

* Figures amended to take account of the row of cones to the righthand side of this lane in the ‘before’ survey reducing the effective lane width by about 1 metre. ** Due to the removal of a traffic lane, lane 3 in the ‘before survey is lane 2 in the ‘after’ survey.

The results from Table 7 show that with the exception of Epsom Road/Boxgrove Road westbound, the actual changes in saturation flow for lane 1 are similar to the predicted ones. At Epsom Road/Boxgrove Road, westbound lane 1 in the ‘after’ survey is in between two red coloured cycle lanes. As this site has the highest cycle flow, motor vehicle drivers may feel more constrained with the presence of cyclists either side of them. This may account for a decrease in saturation flow rather than the predicted increase. For lane 2, the differences between the actual and predicted changes are more noticeable. At Epsom Road/ Boxgrove Road westbound, the actual decrease in saturation flow is much greater than the predicted value. In addition to the reduction in lane width of 0.1 metres, motor

vehicles in lane 2 now have cyclists on their nearside, in the central cycle lane. As with lane 1 at this site, motor vehicle drivers may feel more constrained with the presence of cyclists to their nearside. At the Epsom Road/ A247, there was a slightly larger increase in saturation flow than predicted. The row of cones on the right-hand side of this lane in the ‘before’ survey may have had a greater effect on reducing this lane’s saturation flow than just narrowing its effective width by 1 metre. 5.4 Using OSCADY at junctions with ASLs With the increasing number of ASLs being installed at signal-controlled junctions around the UK, traffic engineers need to be able to model these junctions accurately to predict capacity, queues and delays. OSCADY does not, at present, have the facility to explicitly model junctions with ASLs. However, techniques can still be used in OSCADY to obtain satisfactory results. From Section 5.3, the changes in saturation flow for the ‘lane 1s’ were similar to those predicted by OSCADY. This was assuming that the installation of a nearside cycle lane changes lane 1 from being nearside to non-nearside. In OSCADY, lane widths at the junction have to be in the range of 2 - 10 metres. This excludes cycle lanes which are normally in the range 1.2 – 1.5 metres. However, a dummy lane of 2 metres with zero flow (or higher depending on the cycle flow) can be entered into the program as the cycle lane. This will improve the accuracy of the model, as the adjacent traffic lane is now considered non-nearside. ASLs with central cycle lanes do not affect the nearside nature of the inside lane. However, the widths of the traffic lanes may need to be reduced to take account of the new layout. As with any computer model, the accuracy of the results depends on the accuracy of the data entered. OSCADY allows measured saturation flow values for each lane to be entered directly into the model (as with the OSCADY runs for Epsom Road/Boxgrove Road in Appendix F). If this information is available, no ‘dummy’ lanes are needed; as OSCADY will incorporate these measured values into the model.

6 Observed changes in motor vehicle and bicycle traffic 6.1 Motor vehicle flows and turning proportions Motor vehicle flows and proportions were measured at each site for one peak hour (08:00 – 09:00) and one off-peak hour (10:00 – 11:00). These are shown in Tables 8 and 9. Appendix E shows these results lane by lane. At the two sites where the number of traffic lanes remained the same (London Road/York Road and Epsom Road/A247), the vehicle flows remained similar in the ‘before’ and ‘after’ surveys, with the exception the morning peak hour (08:00 – 09:00) at London Road/York Road. Here, there was an 18% (statistically significant) increase from the ‘before’ survey to the ‘after’ survey. Seasonal differences, however, may account for this difference.

Table 8 Vehicle flows in the ‘before’ and ‘after’ video surveys 08:00 – 09:00 ‘Before’

10:00 – 11:00 ‘After’

‘Before’

‘After’

London Road / York Road 355 419

259

276

Epsom Road / A247 863 813

346

347

Epsom Road / Boxgrove Road (eastbound) 745 687 394

298

Epsom Road / Boxgrove Road (westbound) 1090 1083 662

731

Table 9 Vehicle turning proportions at the four sites (08:00 – 09:00) ‘Before’ Lefts

Straights

‘After’ Rights

Lefts

Straights

Rights

London Road / York Road 0.12 0.88 0.00*

0.12

0.87

0.01

Epsom Road / A247 0.18 0.70

0.21

0.69

0.10

Epsom Road / Boxgrove Road (eastbound) 0.22 0.78 n/a 0.24

0.76

n/a

Epsom Road / Boxgrove Road (westbound) n/a 0.68 0.32 n/a

0.69

0.31

0.12

* Rounded down to 0.00 as less than 0.005.

Epsom Road/Boxgrove Road eastbound had two lanes at the stop line in the ‘before’ survey but only 1 lane in the ‘after’ survey. Vehicle flows on this approach fell by about 8% in the peak hour and 24% in the off-peak hour. The throughput of vehicles was restricted by the removal of lane 2. Queues tended to be longer at the start of green in the ‘after’ survey. Epsom Road/Boxgrove Road westbound had three lanes at the stop line in the ‘before’ survey but only 2 lanes in the ‘after’ survey. In the ‘before’ survey, lanes 1 and 2 were equally useable for straight-ahead traffic. However, 75% of straight-ahead traffic used lane 1 rather than lane 2 in the peak hour (the figure for the off-peak hour was 92%), due to the exit restriction (2 lanes funnel down to one lane within 30 metres of the exit). As a result of this, lane 2 was rarely saturated and exit blocking occurred between 08:20 and 08:40. Exit blocking was almost eliminated in the ‘after’ survey as straight-ahead vehicles were now restricted to one approach lane. The removal of under-used lane 2 had a dramatic effect on the theoretical saturation flow value for the approach (down 38%) but had little effect on the actual throughput of vehicles. Appendix F shows the results from OSCADY for the ‘before’ and ‘after’ Epsom Road/Boxgrove Road junction (the junction where a traffic lane was removed on two 13

approaches). In Appendix F, the Epsom Road/Boxgrove Road westbound approach has been modelled with 3 lanes in the ‘before’ OSCADY run and with 2 lanes in the ‘after’ OSCADY run. The approach is actually one lane with 2 bays in the ‘before’ layout and one lane with a bay in the after layout. However, they have been modelled as lanes because the traffic queue in any of the bays never reaches back as far as the point at which the flare starts, i.e. where one stream of traffic blocks entry to another lane/bay. Also, if the lanes have different turning movements and/or unequal usage rates (as in this case), then modelling them as full lanes may be necessary. Queue and delay information is only provided for specified lanes and not bays in the OSCADY output file. Care must be taken when modelling bays as full lanes as OSCADY can overestimate the capacity of the approach. The user is advised to check that the maximum queue lengths predicted by OSCADY are within the storage capacity for each of the bays. Epsom Road/Boxgrove Road eastbound has been modelled as 2 lanes instead of 1 lane and a bay in the ‘before’ OSCADY run for similar reasons. To enable a comparison of capacity, queues and delays to take place, the ‘before’ vehicle flows were used for both runs. For the eastbound approach (arm A), the mean queues for both lanes 1 and 2 were between 1.6 and 1.7 vehicles. In the ‘after’ situation, lane 1 had a mean queue of between 4.6 and 5.1 vehicles. The inclusive vehicle delay (for traffic movements A to C and A to B) rose from 0.27 to 0.39 minutes per vehicle. In the ‘before’ survey, the degree of saturation on lanes 1 and 2 was 63.8%. In the ‘after’ survey, the degree of saturation on lane 1 was 80.2%. Removing lane 2 on the eastbound approach had a noticeable effect on the capacity, queues and delays of this approach. However, the queues and delays are still relatively small and the lane is still running within capacity. For the westbound approach (arm C), the mean queues for straight-ahead lanes 1 and 2 were between 0.6 and 1.0 vehicles for lane 1 and between 0.1 and 0.2 vehicles for lane 2. In the ‘after’ situation, lane 1 had a mean queue of between 0.8 and 1.6 vehicles. The inclusive queuing delay (for the traffic movement C-A) went up slightly from 0.08 to 0.10 minutes per vehicle. In the ‘before’ survey, the degree of saturation on lanes 1 and 2 was 44.6% and 13.6% respectively. In the ‘after’ survey, the degree of saturation on lane 1 was 53.3%, well within capacity. This means that the removal of lane 2 has had no adverse affect on capacity, queuing or delays of this approach. The maximum degree of saturation at the junction rose from 63.8% to 80.2%. The junction, however, was still running within capacity. The vehicle flow remained similar for the peak hour, with a small increase in the off-peak hour. The majority of motor vehicles at all four sites made a straight-ahead movement. The turning proportions remained similar for both surveys at each site. 6.2 Motor vehicles crossing the first stop line The number of motor vehicles stopping at the first (drivers’) stop line and encroaching on the ASL reservoir while waiting at a red light was recorded. A vehicle was 14

defined to have crossed the first stop line if its front wheels were inside the reservoir. Table 10 shows the numbers and percentages of motor vehicles stopping inside the ASL. Table 10 Numbers and percentages of motor vehicles crossing the first stop line Number of traffic cycles where the front vehicle stops into ASL

Total number of traffic cycles with a vehicle waiting at a red light

Percentage of traffic cycles where the front vehicle stops inside ASL

London Road / York Rd 27 178

15.2%

Epsom Road / A247 53

28.5%

186

Epsom Road / Boxgrove Road (eastbound) 36 184

19.6%

Epsom Road / Boxgrove Road (westbound) 97 388

25.0%

Overall 213

22.8%

936

These non-compliance figures are a little higher than those from other studies quoted in Section 2.2 (18% noncompliance). Higher cycle flows, better signing, education and/or enforcement of the new cycling facility may help reduce the number of vehicles stopping inside the ASL. In the recent ‘before’ and ‘after’ study of pedestrian safety at three signal-controlled junctions in Woking, Camberley and Wokingham (Wall 2000), there was evidence to suggest that drivers respect freshly painted markings rather than old worn out ones. Therefore, renewing all road markings in the vicinity of the ASL may lead to improvements in driver compliance rates. 6.3 Motor vehicle/bicycle interactions A vehicle/bicycle interaction is defined to be movements that could potentially lead to a collision unless either the cyclist or vehicle driver took evasive action. There were no such interactions during the surveys but the following observations were recorded. London Road/York Road The eastbound approach has a dentist’s surgery located within 40m of the ASL. During the ‘after’ survey, several vehicles parked or reversed on the cycle lane and several other vehicles crossed the cycle lane to enter or leave the dentist’s surgery. It is possible that the installation of the cycle lane has encouraged more of this driver behaviour. No interactions with cyclists occurred, but this could potentially be hazardous for cyclists. Other potential interactions were often caused when a right-turning vehicle was waiting for a gap in which to make the manoeuvre. Vehicles making a left-turn or straight-ahead manoeuvre would swerve past the rightturner, often driving into the nearside cycle lane

comparisons can be made. At the three sites where there was no central cycle lane, there were 4 cyclists who turned right. Two used the offside of lane 1, and 2 used the nearside cycle lane to reach the ASL reservoir. There are still benefits for right-turner cyclists, even without the presence of a central cycle lane.

Epsom Road/Boxgrove Road eastbound Many left-turning vehicles would stop partly in the nearside cycle lane at the stop line and then continue to encroach on the cycle lane to make the manoeuvre. This could be potentially dangerous for cyclists. Epsom Road/Boxgrove Road westbound Motorbikes often used the cycle lanes (particularly the central cycle lane) to either overtake a queue of slow moving vehicles or to get to the front of the queue. One cyclist rode in the opposite direction to the main flow down the nearside cycle lane with obvious potential for conflict.

Table 12 Bicycle turning proportions at the four sites 07:00 – 11:00 ‘Before’ Lefts

Epsom Road/A247 A few left-turning vehicles on the eastbound approach strayed into the nearside cycle lane while making their manoeuvre. The above observations show that the newly installed cycle lanes are sometimes blocked and used temporarily by other vehicles. Better signing and enforcement may improve drivers’ compliance.

Straights

‘After’ Rights

Lefts

Straights

Rights

London Road / York Road 0.23 0.77 0.00

0.30

0.60

0.10

Epsom Road / A247 0.20 0.80

0.33

0.67

0.00

Epsom Road / Boxgrove Road (eastbound) 0.15 0.77 0.08 0.07

0.73

0.20

Epsom Road / Boxgrove Road (westbound) n/a 0.86 0.14 n/a

0.75

0.25

0.00

6.4 Bicycle flows and turning proportions The bicycle flows and proportions at each site were measured over a four-hour period from 07:00 – 11:00. The site with the highest number of cyclists was the Epsom Road/Boxgrove Road (westbound) approach that leads to Guildford town centre. The site with the lowest number of cyclists was the Epsom Road/A247 junction that is the crossroads of the Epsom Road dual carriageway and the single carriageway A247. The bicycle flows here were between 1 and 10 cyclists per hour. The ASLs were installed to improve safety for existing cyclists and to encourage more cycling in the local area. The bicycle flows are shown in Table 11. Seasonal differences may account for some of the differences in ‘before’ and ‘after’ flows. Table 11 Bicycle flows in the ‘before’ and ‘after’ video surveys (07:00 – 11:00) Site London Road / York Road Epsom Road / A247

‘Before’

‘After’

Epsom Road / Boxgrove Road (eastbound)

Epsom Road / Boxgrove Road (westbound)

Table 12 shows the turning proportions of cyclists in the ‘before’ and ‘after’ survey at the four sites. As with the vehicle proportions, the straight-ahead movement was the dominant movement at all sites. There was an increase in the proportion of cyclists turning right at all sites except the Epsom Road/A247 site where there were very few cyclists. This could be attributable to the installation of the ASL (and the central cycle lane at the Epsom Road/ Boxgrove Road westbound site), making the right-turn manoeuvre easier and safer-looking for cyclists. However, with such a small sample of cyclists, no accurate

6.5 Queuing positions of cyclists Capacity at the junction may be affected by the queuing/ positioning of waiting cyclists at a red signal, if this queuing/positioning differs as a result of the installation of the ASL. This was therefore investigated along with other parameters relating to cycle traffic. Cyclists queuing/ positioning behaviour was therefore recorded for the ‘before’ and ‘after’ surveys. There was no evidence from the videos of drivers’ being delayed by cyclists queuing in front of the first (drivers’) stop line (inside the ASL reservoir). This was due to the low numbers of cyclists at each site. Figure 8 shows the three categories of queuing position during red (a forth category was those that did not queue). In the ‘after’ surveys, no cyclist queued behind the last queuing vehicle. Tables 13 and 14 show the results. Of those cyclists that queued in front of the drivers’ stop line, additional information was recorded as to their queuing position. Table 15 shows the results for the ‘before’ and ‘after’ surveys. Cyclists positioning in front of the drivers’ stop line was almost always linked to their turning movement, i.e. left-turning cyclists queuing in front of lane 1 positioned themselves near to the kerb (left side). The number of cyclists observed was very small; nevertheless, there was no evidence that the queuing or positioning behaviour of cyclists had any effect on capacity. 6.6 Cyclist approach lane Table 16 shows the cyclist approach lane for the ‘before’ and ‘after’ surveys at the four sites. In the ‘after’ survey, 97% of cyclists approached the junction using the nearside or central cycle lane. This shows that cyclists prefer to use cycle lanes where available. 15

In front of stop line

Behind stop line

Behind queue

Figure 8 Queuing positions of cyclists during red (Note that this picture holds for junctions without ASLs, with the ‘behind stop line cyclist’ being at the front of the queue)

Table 13 Cyclist queuing positions in the ‘before’ surveys at the four sites

Table 14 Cyclist queuing positions in the ‘after’ surveys at the four sites

Queuing position

Queuing position Didn’t queue

Behind stop line (inside the ASL reservoir)

In front of stop line

3 (23%)

London Road / York Road 6 (60%)

4 (40%)

0 (0%)

1 (20%)

Epsom Road / A247 1 (33%)

0 (0%)

2 (67%)

Epsom Road / Boxgrove Road (eastbound) 8 (62%) 1 (8%) 2 (15%)

2 (15%)

Epsom Road / Boxgrove Road (eastbound) 13 (87%) 2 (13%)

0 (0%)

Epsom Road / Boxgrove Road (westbound) 29 (68%) 0 (0%) 4 (9%)

10 (23%)

Epsom Road / Boxgrove Road (westbound) 23 (72%) 8 (25%)

1 (3%)

Didn’t queue

In front of stop line

Behind stop line

Behind queue

London Road / York Road 8 (62%) 0 (0%)

2 (15%)

Epsom Road / A247 3 (60%) 0 (0%)

6.7 Cyclists going through a red light In both the ‘before’ and ‘after’ surveys, there were a small number of cyclists who went through a red light (see Table 17). However, the numbers declined in the ‘after’ survey. All of these cyclists cleared the junction before other traffic proceeded. The majority of these cyclists went either at the start of red (before other streams of traffic received green) or at the end of red (after other streams of traffic had received red). It is unclear why the percentages of cyclists going through a red light are smaller in the ‘after’ survey. It could be due to the re-positioning of the vehicle stop line, 16

allowing waiting cyclists to queue in front of motor vehicles, reducing their delay and the temptation to redrun. However, no statistical comparisons can be made due to the small numbers involved.

7 Questionnaire survey and results A questionnaire survey was carried out at each site with the exception of the A247/Epsom Road site where such a survey was not considered worthwhile due to insufficient cyclists. The surveys were carried as on the following dates:

Table 15 Queuing position in front of the drivers’ stop line ‘Before’ Left

‘After’ Right

Left

Right

London Road / York Road 0 0

Epsom Road / A247 0 0

Epsom Road / Boxgrove Road (eastbound) 1 0 2

Epsom Road / Boxgrove Road (westbound) 0 0 3

* At the Epsom Road / A247 site, no cyclists queued in front of the drivers’ stop line.

Table 16 Cyclist approach lane in the ‘before’ survey’ at the four sites

84% were travelling straight-ahead at the junction.

87% travelled through this junction at least once a week.

80% had travelled through the junction before the installation of the ASL.

97% noticed a difference to the layout of the junction. The main differences mentioned were the cycle lane(s) (some coloured), the ASL and that the cyclist was now able to reach the front of the queue.

51% thought the changes made the junction a lot safer, 20% a little safer and 26% no difference. Only one cyclist out of 24 cyclists at the Epsom Road/Boxgrove Road westbound thought the changes had made the junction more dangerous.

The main reasons given why the junction was thought to be safer were that cyclists were more visible to car drivers, had more road space allocated to them and could now turn right or left more easily. The main reasons given why the changes to the junction made no difference to safety for cyclists were that drivers didn’t always respect the new cycle lanes. 74% thought the changes to the junction made it easier to use for cyclists, with 26% thinking it made little difference.

Approach lane l

‘After’ ‘Before’ Lane 1

Cycle lane (nearside)

Cycle lane (central)

London Road / York Road 13 (100%)

10 (100%)

n/a

Epsom Road / A247 5 (100%)

3 (100%)

n/a

Epsom Road / Boxgrove Road (eastbound) 12 (92%) 13 (87%)

The main reasons why cyclists thought the junction was easier to use were similar to why they thought the junction was safer.

33% stated that before the ASL was installed, they queued in the queue of traffic. 53% stated that they used to queue just behind the stop line with 8% just in front of the stop line. 89% stated that after the ASL was installed, they queued just behind the cyclist stop line.

n/a l

Epsom Road / Boxgrove Road (westbound) 37 (86%) 24 (75%)

8 (25%)

Table 17 Numbers and percentages of cyclists going through a red light Site

‘Before’

‘After’

London Road / York Road Epsom Road / A247 Epsom Road / Boxgrove Road (eastbound) Epsom Road / Boxgrove Road (westbound)

1 (8%) 2 (40%) 3 (23%) 4 (9%)

0 (0%) 0 (0%) 2 (13%) 1 (3%)

London Rd/York Rd November 1, 1999 Epsom Rd/Boxgrove Rd (eastbound and westbound) March 14/15, 2000 All together, 45 questionnaires were completed from the 3 sites: 6 from Epsom Road/Boxgrove Road eastbound, 29 from Epsom Road/Boxgrove Road westbound and 10 from London Road/York Road. Appendix C and D contains the questionnaire layout and the results from the 3 sites. Some of the main results of the responses given were as follows:

94% stated that they normally cycle down the left side of the traffic queue before the ASL was installed. The figure for after the ASL was installed was 91%.

84% thought that the new layout needed no further changes.

Changes mentioned were better signing to inform drivers of the new layout.

49% were travelling to or from work.

85% were travelling on a journey of less than 5 miles.

66% expected their journey to take no more than 20 minutes.

100% stated that they cycled at least once or twice a week.

77% cycled less than 50 miles a week.

56% normally cycle to commute to or from work, 18% for leisure or exercise and 11% to or from school, college or university.

Overall, the newly installed ASLs received a favourable response from the majority of cyclists. They were thought to be safer and easier to use as cyclists were allocated more road space, were more visible to drivers and could turn right much more easily. The main concern expressed was that many drivers of motor vehicles still did not comply 17

with the new layout and still drove into the cycle lane and stopped inside the ASL. It is recommended that better signing, education and enforcement could help to improve driver’s compliance with the new layout.

of cyclists. They were thought to be safer and easier to use as cyclists were allocated more road space, were more visible to drivers and could turn right much more easily. The main concern expressed was that many drivers of motor vehicles still did not comply with the new layout and still drove into the cycle lane and stopped inside the ASL.

8 Conclusions and recommendations 8.2 Recommendations 8.1 Conclusions From the saturation flow formulae and the video surveys, the capacity implications of installations ASLs were assessed. Three possible sources were examined to see if they resulted in a loss of capacity. They were: 1 Moving the drivers’ stop line back 5 metres. 2 The reduced width or removal of traffic lane(s). 3 The different queuing/positioning behaviour of cyclists. Moving back the drivers’ stop line 5 metres had no significant effect on the intergreen times. The experience of many local authorities has been that signal retimings have not been required and capacity has been unaffected. Also, the intergreen timings at the four sites used in the video surveys were unchanged. Moving the drivers’ stop line back should have little effect on the capacity of flares (except where the flare is very short). This was confirmed at the two sites surveyed (Epsom Road/Boxgrove Road eastbound and westbound) which had flared approaches where little change in their capacity was observed. ASLs were shown to have no significant impact on junction capacity unless a traffic lane was removed in order to install them. At the two sites where the number of traffic lanes remained unchanged (London Road/York Road and the Epsom Road/A247) there was a slight (but not statistically significant) increase in saturation flow of 1.5% and 5.5% respectively. At the two sites where a traffic lane was removed (Epsom Road/Boxgrove Road eastbound and westbound), there was a large reduction in saturation flow of 47% and 38% respectively. OSCADY runs on this junction (using data from video) showed a noticeable increase in queues and delays for the eastbound approach but very little change for the westbound approach. This junction, however, was still running within capacity. The changes in capacity that OSCADY predicted were similar to those measured from video for the ‘lane 1s’ (assuming that the new lane 1 is non-nearside and that capacity is reduced by 100 pcu/hr for every metre reduction in lane width) but very different for the ‘lane 2s’. The change in capacity of the ‘lane 2s’ (at Epsom Road/ A247 and Epsom Road/Boxgrove Road westbound) were affected by the presence of a row of cones and a central cycle lane respectively. There was no evidence from the video analysis that cyclist queuing/positioning behaviour had any noticeable effect on capacity (although the bicycle flows at the four sites were small). The questionnaire surveys showed that the newly installed ASLs had a favourable response from the majority 18

Recommendations from the study are as follows: l

The checking and possible extension of the intergreen times and minimum green times, particularly at large signal-controlled junctions and where cyclists are observed to cross the stop line near the end of green, to ensure that cyclists are given adequate clearance time.

Consideration given to the positioning of, and extension times for, vehicle detectors used in the control of traffic signals (not considered in this project).

Use of signal controlled junction modelling computer programs such as OSCADY to assess the impact of changes, especially where a traffic lane is to be removed.

Further encourage the compliance of motorised vehicle drivers with ASLs by the use of, for example, signs, education and/or enforcement, and maintaining the visibility of road markings. Appropriate signs would need to be designed and trialled before use.

Further research to be carried out to establish the safety record of ASLs and establish more precisely the safety and capacity relationships.

9 References Binning J C (1998). Visual OSCADY/4 user guide. Application Guide AG25. Crowthorne: TRL Limited. Burrow I J (1987). OSCADY: a computer program to model capacities, queues and delays at isolated traffic signal junctions. Research Report RR105, Crowthorne: TRL Limited. Cross K D and Fisher G (1977). A study of bicycle/ motor-vehicle accidents: Identification of problem types and countermeasure approaches. National Highway Traffic Safety Administration. Centre for Research and Contract Standardization in Civil Engineering (CROW) (1993). Sign up for the bike. Design Manual for a cycle-friendly infrastructure. The Netherlands: Centre for Research and Contract Standardization in Civil Engineering (CROW). Department of Transport (1981). General principles of control by traffic signals. Department Advice Note TA 16/81. London: Department for Transport. Department of Transport(1986a). Innovatory cycle scheme, Oxford - Parks Road/Broad Street - advanced cycle stop line. Traffic Advisory Leaflet 10/86. London 1986. London: Department for Transport.

Department of Transport (1989). Innovatory cycle scheme, Newark - advanced cycle stop line. Traffic Advisory Leaflet 3/89. London: Department for Transport.

Taylor D B (1993). Analysis of Traffic signal clearance interval requirements for bicycle-automobile mixed traffic. Transportation research record n1405, pp 13 – 20.

Department of Transport (1991). Innovatory cycle scheme, Bristol - advanced cycle stop line. Traffic Advisory Leaflet 6/91. London: Department for Transport.

Traffic Signs Regulations and General Directions (1994). SI 1994/1519. The Stationery Office.

Department of Transport (1993). Advanced stop lines for cyclists. Traffic Advisory Leaflet 8/93. London: Department for Transport. Federal Highway Administration (1988). Manual on uniform traffic control devices. Washington DC: Federal Highway Administration Forester J (1983). Bicycle transportation. Cambridge, Massachusetts: MIT press, pp 265 – 269. Heys C J J M and Vredeveld G (1983). Legal framework for cycle facility: waiting lane for moped riders and cyclists. Verkeerskunde 34, 4-1983 (Department of Transport translation 14672 PR IV/E17). Institute for Transport Studies (1999). The potential for incorporating consideration of bicycle traffic in urban traffic management and control systems – final report. Leeds: Leeds University. Institution of Highways and Transportation (IHT) (1997). Transport and the urban environment. London: Institution of Highways and Transportation Kimber R M, McDonald M and Hounsell N B (1986). The prediction of saturation flows for road junctions controlled by traffic signals. Research Report RR67. Crowthorne: TRL Limited. 3

Kuiper Ing D H (1982). The OFOS - A description of the ‘expanded waiting line for cyclists’ (De ofos - een beschouwing over de opgeblazen fietsopstelstrook). Verkeerskunde 33, 9-1982 (Department of Transport translation 3242).

Watchtel A, Forester J and Pelz D (1995). Signal clearance timing for bicyclists. ITE Journal 1995, 65(3). Wall G T (2000). Road markings to improve pedestrian safety at crossings. Traffic Engineering & Control. April 2000, 41(4) pp 136-140. Wheeler A H (1992). Advanced stop lines for cyclists at Oxford, Newark and Bristol. Research Report RR336. Crowthorne: TRL Limited. Wheeler A H, Leicester M A A and Underwood G (1993). Advanced stop lines for cyclists. Traffic Engineering and Control. 34(2) pp 54-60. Wheeler A H (1995). Advanced stop lines for cyclists - A simplified layout. Traffic Engineering and Control. 36(5) pp 283-289. Wiltshire R L (1992). Traffic signals. Traffic Engineering handbook: fourth edition. Institute of Transportation Engineers. Chapter 9

10 Acknowledgements The authors would like to thank Mr Kaz Banisaied of Surrey County Council for co-operating with the study and providing information about the sites. The authors would also like to thank Messrs Wayne Duerden and Phil Philippou of DfT for their assistance during the research. This work was commissioned and funded by the DfT, CLT Division.

Road Directorate: Denmark Ministry of Transport (1994). Safety of cyclists in urban areas – Danish experiences. Traffic Safety and Environment Report 10. Danish Road Directorate. Ryley T J (1996). Advanced stop lines for cyclists: The role of central cycle lane approaches and signal timings. TRL Report TRL181. Crowthorne: TRL Limited. Salomons W (1985). Evaluation of CPVC-model OFOS in Enschede (Evaluatie CPVC-OFOS in Enschede). Verkeerskunde 36, 7-1985 (Department of Transport translation 3269).

OFOS - Opgeblazen fietsopstelstrook - Dutch term for ASL, loosely translated as expanded bicycle waiting lane.

Appendix A: Photographs of the four sites

Figure A1 London Road / York Road

Figure A2 Epsom Road / A247

Figure A3 Epsom Road / Boxgrove Road (eastbound)

Figure A4 Epsom Road / Boxgrove Road (westbound)

Appendix B: Drawings of the four sites

'Before'

'After'

Figure B1 London Road / York Road

'Before'

'After'

Figure B2 Epsom Road / A247

'Before'

'After'

Figure B3 Epsom Road / Boxgrove Road (eastbound)

'Before'

'After'

Figure B4 Epsom Road / Boxgrove Road (westbound)

Appendix C: ASL questionnaire

Appendix D: ASL questionnaire results

Appendix E: Motor vehicle flow results

Table E1 Vehicle flows in the ‘before’ and ‘after’ video surveys (08:00 - 09:00) Site

Lane 1

Lane 2

Lane 3

London Road / York Road

355

n/a

355

419

n/a

419

Epsom Road / Boxgrove Road (eastbound)

374

371

n/a

745

687

n/a

687

Epsom Road / Boxgrove Road (westbound)

551

186

353

1090

746

337

n/a

1083

Epsom Road / A247

474

389

n/a

863

412

401

n/a

813

Lane 1

Lane 2

Lane 3

Total

Lane 1

Lane 2

Lane 3

Total

Table E2 Vehicle flows in the ‘before’ and ‘after’ video surveys (10:00 - 11:00) Site

Lane 1

Lane 2

Lane 3

Total

London Road / York Road

259

n/a

259

276

n/a

276

Epsom Road / Boxgrove Road (eastbound)

212

182

n/a

394

298

n/a

298

Epsom Road / Boxgrove Road (westbound)

825

269

1162

445

286

n/a

731

Epsom Road / A247

186

160

n/a

346

206

141

n/a

347

Appendix F: OSCADY output files for the Epsom Road / Boxgrove Road junction

Abstract An investigation of the capacity implications of installing Advanced Stop Lines (ASLs) has been carried out by TRL Limited as part of a project entitled Cycling Facilities and Engineering, commissioned by the Charging and Local Transport Division of the Department for Transport. The study included a review of previous research into ASLs in the UK and in the Netherlands; an examination of the theoretical capacity implications of installing ASLs using OSCADY (Optimised Signal Capacity and Delay) the signal-controlled junction modelling computer programme and saturation flow formulae; ‘before’ and ‘after’ video surveys of modified junctions, and questionnaires to examine the attitudes of cyclists. This report of the study concludes with several recommendations.

Related publications TRL285 Cyclists at roundabouts - the effects of ‘continental’ design on predicted safety and capacity by D G Davies, M C Taylor, T J Ryley and M E Halliday. 1997 ( price £40, code H) TRL181 Advanced stop lines for cyclists: the role of central cycle lane approaches and signal timings by T M Ryley. 1996 (price £40, code H) RR336

Advanced stop lines for cyclists at Oxford, Newark and Bristol by A H Wheeler. 1992 (price £25, code E)

RR105

OSCADY: a computer program to model capacities, queues and delays at isolated traffic signal junctions by I J Burrow. 1987 (price £20, code B)

RR67

The prediction of saturation flows for road junctions controlled by traffic signals by R Kimber, M McDonald and N B Hounsell. 1986 (price £20, code B)

AG25

Visual OSCADY/4 user guide by J C Binning. 1998 (price £50, code N)

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