How to cure tunnel vision

PCM treatments are used to reduce crash risk by improving driver speed behaviour, alertness and lane discipline within tunnels

The purpose of the study was to investigate and evaluate the application of low-cost perceptual countermeasure (PCM) treatments in tunnel environments as a means of improving driver speed behaviour and lane discipline within tunnels, thereby reducing crash risk.

The project involved a systematic literature review and stakeholder consultation and an experimental study conducted in a virtual reality driving simulator.

The review identified 33 PCM treatments that had been demonstrated as having a behavioural effect on driver speed behaviour and/or lane discipline.

Stakeholder consultation complemented the literature review in outlining the advantages/disadvantages of these PCMs, particularly in terms of ease of implementation, cost, maintenance, and applicability to a tunnel environment.

Based on the outputs of the literature review and stakeholder consultations, three PCM treatments were selected for evaluation in the virtual reality driving simulator – a striped wall pattern, rumble strips (Edgeline and Centreline), and Pacemaker Lighting.

The experimental study, involving 102 participants, conducted in a virtual reality driving simulator was designed to investigate whether the application of PCM treatments had any impact on drivers’ speed or lateral control in road tunnels and to determine what drivers’ opinions were of the proposed PCM treatments.

The findings revealed that, as implemented in the simulated tunnel environment, the three PCM treatments evaluated had little or no positive effect in either maintaining drivers’ speed or lane position in the simulated tunnel environment.

This does not mean, however, that they were ineffective as treatments, given that there is previous evidence which demonstrates that one of the treatments (Pacemaker lighting) has been found to be effective in a real tunnel environment, and that rumble strips are effective on real open roads.

Further research is recommended to determine whether certain critical proposed modifications to the experimental design utilised in this study would make these PCMs more effective in inducing positive changes in driving behaviour in the virtual tunnel environment.

Subjective feedback from study participants indicated that none of the PCMs evaluated were perceived to compromise their safety.

On the contrary, evidence from this study indicates that the tunnels treated with PCMs were rated as being significantly more visually interesting, more attractive, induced less boredom and less sleepiness (striped wall patterns), and were significantly more memorable (Pacemaker lighting), compared to the untreated tunnels.

Sidewall striped patterns

A single simulator study by Manser and Hancock (2007) found that when drivers were exposed to wide to thin stripes on a tunnel wall, they reduced their travelling speed.

This effect was further attenuated when the stripes on the wall had texture added to them.

This finding provides preliminary evidence of the efficacy of installing wide to thin stripes along a tunnel wall in reducing speed although this finding has yet to be replicated.

Across the ratings, the stakeholders indicated that this was a mid-range treatment with respect to modifying speed.

The cost and maintenance associated with this treatment might be high depending on how it is implemented. It was deemed suitable for a tunnel environment.

Additional comments from the stakeholders suggested that considerations would need to be made regarding the painting and cleaning of the tunnel walls with this treatment.

A single simulator study by Wan et al. (2016) found that red arrows presented at a temporal frequency of between 4.45 Hz and 7.01Hz were effective in causing drivers to overestimate their speed while travelling through a tunnel.

This has yet to be tested to determine whether it modifies driver behaviour or simply their perception. Further research is therefore required to determine whether this combination of arrow features results in drivers travelling at slower speeds in a tunnel environment.

Across the ratings, the stakeholders indicated that this form of treatment is a mid-range treatment but would be highly suitable for a tunnel environment.

The cost and maintenance of this treatment, according to the stakeholders, could be high due to issues with painting and the cleaning of tunnel walls.

Furthermore, stakeholders raised potential issues around the impact this sort of treatment would have on tunnel luminance due to reducing the reflective surface of the tunnel walls by adding in colour.

Therefore, this sort of treatment would need to be investigated in conjunction with luminance to ensure it does not impact on overall visibility in a tunnel.

Optical speed circles

A simulator study by Hussain et al. (2018) found that optical speed circles were effective at reducing speed on the approach to an intersection.

This finding has yet to be tested on a road without an intersection and has not yet been trialled in a tunnel environment.

Across the ratings, the stakeholders indicated that this would be a midrange treatment, overall. The efficacy of this PCM in modifying speed was unclear for stakeholders with some questions raised over applicability to a tunnel environment; therefore, the most suitable display would need to be investigated.

The maintenance and cost of implementation of this treatment were rated average on the rating scale, but comments suggested that the paint associated with this form of roadway marking and constant maintenance to ensure the visibility of the circles would be an important factor to consider.

The stakeholders suggested investigating the impact these circles would have on drivers in terms of confusion and sensory overload.

Peripheral transverse lines

Peripheral transverse lines have consistently been demonstrated to result in small but significant reductions in speed in both simulator and on-road studies.

The efficacy of this treatment in improving speed in a tunnel environment has not yet been tested.

Across the ratings, stakeholders indicated that this would be a suitable treatment for tunnels, receiving the second highest overall rating.

The cost, maintenance and ease of implementation ratings are above average. However their efficacy at reducing speed and improving lane position was less certain.

The comments from the stakeholders suggested that they could introduce confusion to drivers and interfere with other lane markings. The effect on drivers would therefore need to be investigated.

aPriL- MaY 2022

Rumble strips plus dragons teeth

A simulator study by Montella et al. (2011) tested a variety of combined PCM treatments for their efficacy at reducing speed and lateral position deviation on approach to an intersection.

They found the combination of Rumble Strips and dragons teeth resulted in a significant decrease in speed on approach to an intersection and recommended this treatment as one of the most effective they trialled.

This combined treatment has not yet been tested in a tunnel environment. It is important to note that this treatment also has demonstrated efficacy in improving lane position.

Across the ratings, the stakeholders indicated that this was a suitable treatment with average effectiveness ratings for both speed and lane position. The cost and maintenance required were rated as average.

The ease of implementation of this treatment was rated as high but applicability to a tunnel was more uncertain. There were some concerns raised over maintenance costs due to high wear of the paint markings

Pacemaker lighting

The Pacemaker Lighting treatment was identified by a member of the Austroads Tunnel Task Force as an emerging and innovative PCM treatment type.

Pacemaker Lighting involve the use of LED lights installed on the side walls

Perceptual lane narrowing

There were mixed findings about the efficacy of narrowing the lane widths at reducing speeds. There were key methodological differences between the studies with one study (Rosey et al. 2009) finding that it was not effective at a lane width of three metres but another (Godley et al. 2004) finding that when lane width was reduced to 2.5m, there were reductions in speed.

The recommendation by Godley et al. was that lanes of less than three metres wide were effective at reducing speed.

This suggests that a width of less than 3m might be effective at reducing speeds but is yet to be tested in a tunnel environment.

It is important to note that this treatment also has demonstrated efficacy at improving lane position. Across the ratings, the for the Dragons teeth component of the treatment.

of tunnels that flash in a sequence in the direction of travel of vehicles.

They operate on the principle of “phototaxis” (the movement with directionality toward the photic stimulation) and were implemented in a tunnel in Tokyo, Japan, as a method to support recovery of speed during congestion (Kato, Nakagawa, Hashimoto, & Inaba, 2015).

In a five-month evaluation, Kato et al. (2015) found that the Pacemaker Lightings were able to reduce congestion at the treatment sites by 60 percent, and the congestion of the whole route reduced by 20 percent. The reductions in congestion were attributed to the Pacemaker Lights facilitating better speed maintenance within the tunnels

stakeholders indicated that this was the best of the proposed PCM options.

Concerns were raised over the initial costs involved in order to remove ghost markings; but once implemented the maintenance and costs were rated as reasonable.

Some concerns were raised over the effect the space reduction might have on feelings of comfort and anxiety by drivers which have been suggested to investigate.

Lane Position

Both the simulator study by Godley et al. (2004) and simulator and on-road studies by Rosey et al. (2009) found significant improvements in lateral positioning when the width of the lane was narrowed.

Drivers were found to position themselves better in the centre of their lane. This improvement in lateral position was found for lanes of three metres wide and 2.5m wide.

The efficacy of this treatment has been tested both in simulators and on-road but not in a tunnel environment. This treatment also has demonstrated efficacy at improving speed.

Across the ratings, the stakeholders indicated that this was the best of the proposed PCM options. Concerns were raised over the initial costs involved in order to remove ghost markings; but once implemented the maintenance and costs were rated as reasonable. Some concerns were raised over the effect the space reduction might have on feelings of comfort and anxiety by drivers which have been suggested to be investigated. In a review of the PCMs that were evaluated to improve lane keeping, five treatments were identified as potential options for trial in a simulator: Centreline rumble sticks, rumble sticks plus dragon’s teeth, LED lighting, Pacemaker lighting and edgeline rumble sticks

Centre line Rumble Sticks

Three studies have found that Centreline Rumble Strips improve the positioning of drivers forcing them to drive closer to the middle of their lane (Rosey et al. 2008; Auberlet et al. 2010; Auberlet et al. 2012). This improvement has been demonstrated to be equivalent to a tyre width. A review by Hatfield et al. (2008) found that Centreline Rumble Strips reduced crashes by 25 percent, with the inference being that they reduce crashes by improving lane keeping. This improvement in lane position has been found in both simulators and onroad but has not been tested in a tunnel environment. Across the ratings, stakeholders indicated that this treatment would be effective at modifying lane position, but concerns were raised over applicability to a tunnel environment. The most common recurring concern was associated with the noise the rumble strips would make and the potential for this to have an echo effect in a tunnel and confuse drivers. There were also concerns raised over the impact centreline strips would have on motorcyclists when changing lanes and for stopping distances.

LED Lighting

LED lighting was found to have small benefits at improving lane keeping and speed on approach to, and exits from, tunnels. A simulator study by Domenichini et al. (2017) found that when in a tunnel with LED lighting drivers responded earlier to hazards and acted in a more efficient way. This suggests that LED lighting has demonstrated small but significant safety benefits across the board. Across the ratings, the stakeholders indicated that, while LED lighting is highly applicable to a tunnel environment, the implementation will be difficult, and the costs associated with this are high. Stakeholders noted that in some tunnels it is not possible to retrofit LED lighting systems but that they should be considered for all new tunnels.

Edgeline rumble strips

Edgeline Rumble Strips have not been examined in relation to lane positioning but a review by Hatfield et al. (2008) found that they reduce off-road crashes by approximately 22 percent. They were also found to not result in an increase in head-on crashes in on-road trials. The inference from this review and on-road trial is that the reduction in crashes with Edgeline rumble strips is a result of improved lane keeping. The efficacy of this treatment in improving lane positioning and crashes has not been tested in a tunnel environment. The ratings from the stakeholders for this PCM are provided below in Table 2.14. Across the ratings, the stakeholders indicated that this was applicable to a tunnel environment but there was uncertainty over its efficacy in improving driver behaviours of speed and lane position. Again, concerns were raised over noise in a tunnel environment of the Rumble Strips and the potential implications from a driver hitting the strip and then overcorrecting. These factors would therefore need to be investigated.

Austroads, of which Waka Kotahi NZ Transport Agency is a member, has produced this report as part of its work to promote improved Australian and New Zealand transport outcomes by providing expert technical input on road and road transport issues. It was prepared by Prasannah Prabhakharan, Julius R. Secadiningrat, Michael A. Regan, Joanne Bennett, Mitchell Cunningham, Aleksa Zlojutro, Vinayak Dixit. Project manager Geoff McKernan. www.austroads.com.au