Street lighting for preventing road traffic injuries: Cochrane systematic review

Abstract

Assessed as up to date: 2008/10/14

Background

Road traffic crashes are a major cause of death and injury, especially in low and middle-income countries. It is estimated that road traffic injuries will have risen from ninth to third in world disease burden rankings by 2020, accounting for 2.3 million deaths per year globally. Street lighting has been suggested as a relatively low-cost intervention with the potential to prevent traffic crashes.

To assess the effects of street lighting on injuries caused by road traffic crashes.

We searched the Cochrane Injuries Group's Specialised Register, CENTRAL, MEDLINE, EMBASE, TRANSPORT and the Australian Transport Index. We also searched the Internet and checked reference lists of relevant papers. The search was not restricted by language or publication status. The searches were conducted to October 2008.

Randomised controlled trials, non-randomised controlled trials and controlled before-after studies, comparing new street lighting with unlit roads, or improved street lighting with the pre-existing lighting level.

Two authors screened search results, extracted data, assessed risk of bias and analysed the data.

We found 17 controlled before-after studies of street lighting, all reporting crash data, of which 15 contributed data to the meta-analysis. Seven trials included a designated control site; the other ten collected data at one site with the day-time data being used as the control. The methodological quality of the trials was generally poor.

Three trials compared street lighting with an area control on total crashes; pooled rate ratio (RR) = 0.45 (95% confidence interval (CI) 0.29 to 0.69). Two trials compared street lighting with an area control on total injury crashes (all severities); RR = 0.78 (95% CI 0.63 to 0.97). No trials compared the number of fatal crashes with an area control.

Eleven trials compared street lighting with a day-time control on total crashes; pooled RR = 0.68 (95% CI 0.57 to 0.82). Six trials compared street lighting with a day-time control on total injury crashes; pooled RR = 0.68 (95% CI 0.61 to 0.77). Four trials compared street lighting with a day-time control on fatal crashes; pooled RR = 0.34 (95% CI 0.17 to 0.68).

The results from this systematic review suggest that street lighting may prevent road traffic crashes, injuries and fatalities. However, further well designed studies are needed to determine the effectiveness of street lighting, particularly in middle and low-income countries.

Author(s)

Beyer Fiona R, Ker Katharine

Summary

Street lighting for preventing road traffic crashes and injuries

Road traffic crashes are a major cause of death and injury, especially in low and middle-income countries. Worldwide, each year over a million people are killed and some ten million people are permanently disabled in road traffic crashes. Furthermore, it is estimated that road traffic injuries will have risen from ninth to third in world disease burden rankings by 2020, and will account for 2.3 million deaths each year globally.

Street lighting has been suggested as a relatively low-cost intervention with the potential to prevent traffic crashes. Street lighting may improve a driver's visual capabilities and ability to detect roadway hazards. However, it is also argued that street lighting could have an adverse effect on road safety; drivers may 'feel' safer because lighting gives them improved visibility which could result in them increasing speed and reducing concentration.

This systematic review was conducted to assess how street lighting affects the occurrence of road traffic crashes and associated injuries. The authors searched for all controlled trials comparing the effects of new street lighting with unlit roads, or improved street lighting with the pre-existing lighting level. They found 17 controlled before-after studies, all of which were conducted in high-income countries. Twelve studies investigated the effects of newly installed street lighting, four the effects of improved lighting and one investigated both new and improved lighting. Five of the studies compared the effects of street lighting with a separate area control, while the remaining 12 used data from a day-time control. The authors were able to pool crash or injury data from 15 of the studies. The risk of bias in these studies was judged to be high.

The results indicate that street lighting can prevent road traffic crashes, injuries and fatalities. This finding might be of particular interest to low and middle-income countries where the policy on street lighting is less developed and the installation of suitable lighting systems is less common than in high-income countries. However, further well designed studies are needed to determine the effectiveness of street lighting in middle and low-income countries.

Reviewer's Conclusions

Implications for practice

The results of this review suggest that street lighting may prevent road traffic crashes, injuries and fatalities. The results are unlikely to have a significant impact on the road planning policy of high-income countries. It is already widely accepted that street lighting has a safety function and has become an integral part of road design. However, in the UK, an increasing number of local councils are turning off public street lighting in certain areas in a move to reduce costs and carbon emissions. The potential adverse road safety impact of such a policy should be carefully considered in light of the findings of this review.

In low and middle-income countries, however the policy on street lighting is less developed and the installation of suitable lighting systems is less common. Therefore the positive findings of this review may further encourage attention to the improvement of street lighting in lower income countries as a road safety measure.

Implications for research

No randomised controlled trials were identified in this review. Additional well designed controlled trials are needed to estimate effects accurately, with a focus on effectiveness in middle and lower-income countries. In particular, further research investigating the impact of street lighting on vulnerable road users is required.