Street Lighting and Road Safety
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There are a number of benefits to street lighting. It can be used to promote security in urban areas and to increase the quality of life by artificially extending the hours in which it is light so that activity can take place. Street lighting also improves safety for drivers, riders, and pedestrians.
Driving outside of daylight hours is more dangerous – only a quarter of all travel by car drivers is between the hours of 7pm and 8am, yet this period accounts for 40% of fatal and serious injuries to the same group 1. Pedestrians and vulnerable road users suffer from decreased visibility in the dark too. For these reason, ways of reducing the risk to all road users during the hours of darkness must be found.
A study for the Department for Transport 2 in 2003 found that road safety was perceived as a key benefit for street lighting improvement. In the study, 73% of respondents agreed that 'better street lighting would improve the safety of children, and 63.8% agreed that 'improved street lighting would lead to fewer accidents on the roads'.
Since this study there has been a trend to either switch off or dim street lighting. A study 3 led by researchers from the London school of Hygiene and Tropical Medicine was carried out in 2015 to assess the impact of this practice. Researchers analysed 14 years of data from 62 local authorities who had implemented light reducing measures including reducing the number of lights switched on, dimming lights and LED lamp upgrades. To assess the road safety implications all roads in the participating authorities were examined, looking at: lighting used and the number of traffic collisions that happened at night relative to the day between 2000-13.The study concluded that there was no evidence of an association between reduced lighting and night-time collisions across England and Wales.
A further study 4 undertaken by the same academic body in 2015 provides an insight in to the public's perception of the importance of street lighting. This research looked at the determinants of health and wellbeing in relation to switching off and dimming of street lighting. Eight local authorities that had carried out, or were planning, a range of reduced lighting measures at night were chosen for the study. Quality data analysis was undertaken with residents' views being collected through interviews, transcripts, field notes, documentary data and open comments on questionnaires.
The report concluded that in a random sample of the population in affected and non-affected streets, there was little evidence that the introduction of part-night lighting had made significant differences to wellbeing, except in residents' feelings of personal security. Even where there were strongly held views or anxieties few reported direct impacts on outcomes such as mobility.
As well as the public perception that better lighting improves safety, earlier research that compares the quality of road lighting to accident reduction, found that it improves safety.
- A literature review 5 of studies relating the presence of lighting to accident reduction concluded that "On urban main roads, with mainly a traffic function, a reduction in accidents involving injuries of approximately 30% can be expected at night following an improvement in the lighting from very bad to good"
- A Japanese report 6 that looked at the reduction in accidents at junctions, following the provision of lighting, found that there was a 43% reduction in night-time accidents. It also found that the effectiveness of lighting in preventing accidents depended on its illuminance, and that the brighter the lighting, the better it is at preventing accidents. However it did not define an upper limit to brightness beyond which further brightening would have no, or a negative, effect.
- A report by SWOV 7 found that a 'relatively large proportion' of night-time accidents occur on unlit road sections. It also found that 'there are modest indications that the average injury severity and the proportion of accidents at bends is somewhat greater on unlit road sections'.
- A report conducted by the University of Manchester Institute of Science and Technology 8 found that low illumination is a major contributory factor in the night-time fatality rate.
- A more recent follow up study 9 by some of the same authors using the same methodology reached the same conclusion and presented up to date figures showing the effect that lighting has on the likelihood of fatal injury.
- On motorways, 2.6% of accidents are fatal where street lighting is present, compared to 4.3% of accidents where it is not
- On built up roads, 1.3% of accidents are fatal where street lighting are present, compared to 1.9% of accidents where it is not
- Similarly, on non-built up roads 3.1% of accidents are fatal in lit conditions, rising to 4.9% in areas without street lights
Both studies cited an increase in thinking and stopping distances in non-optimal night-time conditions as the reason why the rate increases. They concluded that on average the presence of street lighting reduces the severity of injuries by a factor of 3.
This raises the concern about the relationship between the safety that a driver perceives and the actual level of safety, and how drivers behave in both conditions. If a driver perceives a better level of safety due to lighting, and therefore behaves in a more dangerous manner when their vision is not noticeably improved, could this lead to a greater increase in risk than simply reducing the luminance would suggest?
The latest evidence 3 concluded that there was no evidence of an association between reduced lighting and night-time collisions across England and Wales. However, previous research 9 has concluded that there are positive safety benefits. Surveys have shown that the public are in favour of street lighting as a way of improving road safety and that, if anything, it needs to be improved in some areas.
There are economic and environmental reasons why some organisations may wish to reduce the amount of lighting. However there are safety reasons why lighting needs to be available.
In some locations, a reduction in lighting quality may not increase the risk of an accident. However, there is the danger that an unconsidered removal or reduction in quality could actually increase accidents and their severity.
Therefore, when considering removal or dimming of lights, location based traffic and accident evidence should be assessed. Accident rates should be monitored to ensure that sacrificing the quality of lighting does not unduly increase the risk. Increases in risk may ultimately lead to lives being lost.
- Night-time accidents, a scoping study; Report to the AA Trust; H. Ward et al, UCL
- The value of improved street lighting in rural areas; Ken Willis et al, Centre for Research in Environmental Appraisal & Management, University of Newcastle upon Tyne, October 2003
- The effect of reduced street lighting on road casualties and crime in England and Wales; controlled interrupted time series analysis, R Steinbach, C Perkins, L Tompson, S Johnson, B Armstrong, J Green, C Grundy, P Wilkinson, P Edwards, Journal of Epidemiology & Community Health 2015
- Reduced street lighting at night and health: A rapid appraisal of public views in England and Wales; Judith Green, Chloe Perkins, Rebecca Steinbach, Phil Edwards, Faculty of Public Health and Policy, London School of Hygiene & Tropical Medicine, May 2015
- The relationship between the level of public lighting and traffic safety; a supplementary literature study, D.A.Schreuder. R-88-10. Leidschendam, SWOV, 1988
- Research on the interrelation between illuminance at intersections and the reduction in traffic accidents; H Oya et al; The Lighting Journal, Vol 68 pp 14-21
- Street lighting and road safety on motorways; A.A. Vis D-94-18, SWOV 1994
- Road traffic accidents: the impact of lighting; I Murrey et al, The Lighting Journal, Vol 63 pp 42-46
- Road traffic casualties: understanding the night-time death toll; S Planis et al, Injury Prevention Vol 12 Issue 2 pp125-128