The objective of this study was to examine the impact of street lighting on the incidence of injury and death caused by road traffic crashes. The global epidemic of road traffic deaths and injuries is only in its infancy and yet, according to the World Health Organization, road traffic injuries (RTIs) are already the leading cause of death by injury, the tenth leading cause of all deaths and the ninth leading contributor to the burden of disease worldwide (estimated using disability adjusted life years - DALYs). A million people die each year on the world's roads, and only HIV/AIDS causes more deaths among people younger than 44 years of age (Krug 1999). Crude estimates indicate that RTIs cost 1-2% of a country's gross national product (GNP), depending upon that country's degree of motorisation. The UK Transport Research Laboratory calculates that this amounts to a global bill of $578 billion (Jacobs 2000) but, despite these figures, average spending on road safety measures in 1990 was only $1 for every DALY caused by road traffic crashes (Peden 2003). And the problem is only likely to become more severe as private car ownership continues to rise. By 2020 it is predicted that RTIs will have risen to third in the world disease burden rankings, accounting for 2.3 million deaths annually, almost 90% of which will afflict lower and middle-income countries. As far back as 1991, road deaths in China equalled those in the United States, despite there being one hundred times fewer cars per thousand population (5 vs 770) (Roberts 1995). The advance of motorisation is likely to further exaggerate this disparity. Few countries outside the western world have an infrastructure suited for, and capable of coping with, excessive car travel. The roads in these countries are already dangerous; they are only likely to become more so. Road traffic crashes should not be dismissed as the unfortunate culmination of chance, but are best considered as being dependent on epidemiological risk factors. Being young, male, poor, or a pedestrian, pedal cyclist or motorist will all increase an individual's risk of involvement in a road traffic crash, as will driving at night (Zwi 1993). Only 25% of road travel takes place at night but over 50% of crashes occur during the hours of darkness, meaning that a night-time road user is three to four times more likely to be involved in one than his/her daytime counterpart. Public lighting was first introduced in both London and New York in 1882, well before the rise of the motorcar. The popularity of street lighting lay in the assistance it gave to the maintenance of social order and the reduction of crime. Scientific interest in injury prevention did not follow for another seventy years or so. Then, during the 1950s and 1960s, studies began to be conducted to assess the role street lighting could play in making safe the ever busier and more dangerous roads of motorised nations. The International Commission on Illumination (CIE) argued in 1960 that lighting reduced accidents on urban traffic routes (original report updated in 1992 - CIE 1992) and work during the following decade suggested the magnitude of this reduction to be approximately 30%. Since then, the provision of street lighting has generally been justified on the basis of the cost savings expected from increased service and safety levels (Macauley 1989). It is perhaps unfortunate that the readiness with which the 30% figure was accepted has dissuaded researchers from conducting as much research in the field as they might otherwise have done. Although research continued throughout the 1970s, the majority of work is now 30 years or more out of date. Much has changed on the world's roads since then; traffic volume has swelled universally, including in countries where automotive travel was previously rare. As such, the estimates derived from early work may not apply to modern roads and driver behaviour. Furthermore, estimations for the effect of street lighting have never been investigated in many low and middle-income countries, where there are more vulnerable road users who are less likely to be segregated from traffic. It is these countries that now carry the greatest burden from road traffic crashes. Street lighting may affect road traffic crashes in three ways. First, it may improve a driver's visual capabilities and ability to detect roadway hazards, especially among older drivers. Rockwell found that when lighting quality was increased drivers exhibited earlier detection of intersections, earlier gas pedal release and speed reduction, suggesting an improvement in driver visual certainty (Rockwell 1976). In addition to these effects, street lighting can reduce the contrast between headlight glare and the environment, preventing loss of visual certainty from contrast adaptation. However, some argue that these improvements also permit changes in driver behaviour that may have an adverse affect on safety, due to the risk compensation effect. This is a behavioural adaptation to a perceived low-risk situation: if drivers "feel" safer because lighting gives them improved visibility, then they may increase speed and reduce concentration (Assum 1999). If correct, this implies that overall risk remains constant over time, regardless of the intervention, because drivers adapt their behaviour to the reduced risk situation. Finally, it must be considered that approximately 10% of all road traffic crashes involve a collision with a stationary roadside object, be it a tree, a telegraph pole or a street light. Increasing the number of street lights on any given road could theoretically increase the crash potential of that road, reducing any of the safety benefit provided by street lighting. A literature review analysed the results of 11 previous investigations, and found that there was not sufficient evidence to support the claim that lighting reduced road traffic crashes (Vincent 1983). Furthermore, almost all of the eleven included studies were found inadequate in some respect, including inappropriate site selection and outcome evaluation. Vincent concluded that, despite a widespread faith in street lighting, there was scant evidence in its support. He called for further research on driver reaction to hazards under lit conditions, in order to establish whether this faith was justified. The literature was re-examined by Elvik, who did not share Vincent's concerns about the validity of the data and concluded that street lighting may reduce night time fatalities by as much as 65% and night time injuries by 30% (Elvik 1995). Nevertheless, he still accepted that the effect of public lighting varies with accident type and severity, and that numerous other variables may further complicate this effect. The contrasting opinions of different authors and the rapidly changing state of global road behaviour, contrasted with the absence of recent investigation, necessitate a rigorous re-examination of the available evidence, which will be provided by this systematic review. (Author/publisher)
Abstract