Cycling in the Dark

CYCLING IN THE DARK

Darkness puts people off from cycling because of increased concerns about safety. Analysis of crash records shows these concerns are well-founded. The risk of a cyclist being involved in a crash is significantly greater when it is dark, and the risk of it being fatal, particularly when there is no road lighting present

By Dr Jim Uttley and Professor Steve Fotios

Cycling is a healthy, sustainable and economical mode of transport. Despite this, only 2% of trips are made by bicycle in the UK each year.

Gear Change, the Department for Transport’s 2022 vision statement for cycling, sets out the government’s desire to see half of all journeys in towns and cities walked or cycled, meaning local authorities have an obligation to promote cycling. In this article we ask what road lighting can do to support cycling after dark.

Many factors put people off from cycling, such as the physical effort involved, weather conditions and safety concerns.

Another significant factor is darkness. A survey of 1,402 people in Canada found that making a trip after dark on a route that was not well lit was one of the top barriers to choosing to cycle, particularly for people new to cycling [1] This is illustrated in figure 1. A survey by Sustrans, a UK cycling charity, found that only 36% of men and 23% of women felt safe cycling during hours of darkness [2]

Measurement of cycling behaviour in Birmingham and Cambridge also suggests there is a significant drop in cyclist

numbers after dark, even after accounting for time of day and seasonal changes such as weather conditions [3,4]

CRASH RISK AFTER DARK

One reason why darkness puts people off from cycling is likely to be the reduction in visibility that occurs after dark – it is more difficult to see and to be seen.

It is more difficult for cyclists to see potential hazards such as potholes and debris in the path, and drivers have greater difficulty seeing and recognising cyclists. This leads to cyclists feeling more vulnerable after dark.

Are these concerns borne out in the statistics on crashes involving cyclists? To answer this, we can consult ‘STATS19’, data from the reporting form used by police to record details of road traffic crashes resulting in a personal injury.

STATS19 provides a range of information about crashes, including the time they occurred, details about those involved and the surrounding environment, and the light conditions at the time of the crash. Figure 2 shows the annual number of crashes involving a cyclist casualty in daylight and darkness, for 2004 to 2021.

At first sight, the data in figure 2 suggests crashes after dark are relatively few, representing only 20% of all crashes involving a cyclist casualty. But this does not tell us the complete story. This is because it does not account for changes in the numbers of people travelling (here, cyclists and drivers) at different times of day.

To make a better estimate of crash risk in daylight and darkness, in our research we first focus on a particular time of day, what is known as a ‘case’ hour. Here we used 6pm to 7pm in the evening, chosen because it is in daylight for one part of the year and in darkness for another part.

Comparing crash counts when this hour is in daylight or darkness is not sufficient though, as it does not account for seasonal changes, particularly weather conditions, that are likely to affect crash risk and the number of people cycling.

We therefore also compare crash counts over a ‘control’ hour. Here we use 2pm to 3pm because that hour is in daylight for the whole year.

We use an odds ratio to compare the numbers of crashes in daylight and darkness in the evening alongside the numbers of

crashes for the same times of year during the control hour. An odds ratio greater than 1.0 indicates that crash risk is greater after dark than in daylight.

Our previous work has shown that darkness significantly reduces the number of people cycling, even after accounting for time of day and changes in weather conditions [3,4]. We therefore used these data to weight crash counts by the numbers of people cycling at different times of day. These weighted counts are shown in figure 3.

From these data we calculated an odds ratio of 1.27. This shows the risk of a crash after dark is greater than during daylight.

The 95% confidence interval (1.22-1.33) shows that is a statistically significant result.

The increase in risk of a cyclist being involved in a crash after dark suggests there is potential for road lighting to mitigate that risk. This can be demonstrated by comparing the crash statistics for locations that are lit and unlit, a factor recorded in STATS19.

The numbers for fatalities are shown in table 1. The resulting odds ratio of 7.83 (95% CI: 6.58-9.30) shows that on unlit roads there is a massive increase in the risk of a cyclist fatality after dark.

DARKNESS AND CYCLIST FATALITIES

We focused on fatalities in that analysis of lit and unlit roads because injury severity is expected to increase after dark.

In daylight, drivers are able to see greater distances ahead, giving more opportunity to see hazards in time to avoid the collision altogether, or reduce the

impact speed and hence injury severity. After dark, when visual function is impaired, hazard detection distances and time available for braking can be reduced. The numbers of fatal and non-fatal cyclist crashes are shown in table 2. The odds ratio of 1.40 (95% CI: 1.27-1.54) shows this greater risk of fatality after dark than in daylight.

CYCLE LIGHTING

Cyclists also have a responsibility for their own safety. They can (and should) have front and rear lights fitted to their bicycle – the use of cycle-mounted lights being a legal requirement after dark in the UK. However, repeated field surveys have shown that many cyclists do not use lights after dark [5]. One possible factor is perceived visibility to others [6] . Cyclists

think they are visible and conspicuous to drivers at much greater distances than the distance at which drivers actually see them.

SUMMARY

After dark there is a much greater risk of cyclists suffering a fatal injury in a road crash. This risk is greater on unlit roads than on lit roads which shows that road lighting is serving a purpose.

What we need to know next is what are the ideal lighting conditions for reducing cyclists’ crash risk so that the costs and benefits of road lighting can be optimised?

Appropriate and well-designed lighting is essential if we are to keep existing cyclists safe and encourage more people to cycle in the future.

Dr Jim Uttley BSc PGDip PhD is lecturer in architectural science and Professor Steve Fotios PhD BEng(Hons), PGCE, FHEA, FSLL, MILP, MEI is professor of lighting and visual perception in the School of Architecture at Sheffield University

[1] Winters M, Davidson G, Kao D, Teschke K. ‘Motivators and deterrents of bicycling: comparing influences on decisions to ride’. Transportation. 2011; 38(1): pp.153-68. [2] Sustrans. ‘Bike Life: Inclusive city cycling’. 2018. Available from: https://www.sustrans.org.uk/media/2930/2930.pdf [3] Uttley J, Fotios S, Lovelace R. ‘Road lighting density and brightness linked with increased cycling rates after dark’. PlosONE 2020; 15(5): e0233105. [4] Fotios S, Robbins C J. ‘Effect of ambient light on the numbers of motorized vehicles, cyclists and pedestrians’. Transportation Research Record 2022; 2676(2): pp.593-605. [5] McGuire L, Smith N. ‘Cycling safety: injury prevention in Oxford cyclists. Injury Prevention’. 2000; 6(4): pp.285-7. [6] Wood J M, Tyrrell R A, Marszalek R, Lacherez P, Carberry T, Chu B S, King M J. ‘Cyclist visibility at night: perceptions of visibility do not necessarily match reality’. Journal of the Australasian College of Road Safety. 2010; 21(3): pp.56-60.