Safety effects of dynamic speed limits on motorways

Dynamic speed limits (DSL) are limits that change according to real-time traffic, road or weather conditions. In DSL-schemes road users are typically informed of speed limit changes by electronic signs that are housed within gantries situated above lanes. Dynamic speed limit systems are increasingly applied worldwide, usually on motorways. One of the objectives of dynamic speed limits is to improve traffic safety through reductions in speed variations within and across lanes and between upstream and downstream flows. This paper shows the results of an empirical evaluation of the effects on traffic safety of a dynamic speed limit system on motorways in Flanders, Belgium. The evaluation was done by means of a before-after analysis of crashes, completed with a cost-benefit analysis. The results show that the number of injury crashes decreased significantly (-18%) after the introduction of the system. A separate analysis for serious and fatal injury crashes revealed a non-significant decrease of 6%. A distinction according to crash type showed an almost significant decrease of 20% in the number of rear-end crashes whereas the number of single-vehicle crashes decreased by 15% (ns). However, no effect was found for side crashes. In addition to the analysis of the effects, a cost-benefit analysis was applied. The costs of the implementation of these systems were compared with the benefits of crash prevention. The cost-benefit analyses of the crash effects showed a benefits-to-costs ratio of approximately 0.7, which means that the costs tend to exceed the benefits. Taking into account the important margins of uncertainty with respect to both costs and benefits, we have also explored how the net benefits are affected by some key assumptions. The general conclusion is that there is no convincing evidence that the costs of the system currently outweigh the expected benefits in terms of crash prevention.This research was carried out within the framework of the Policy Research Centre on Traffic Safety and was partly supported by a grant from the Research Foundation Flanders. The content of this paper is the sole responsibility of the authors.Safety; Crash; Motorway; Dynamic speed limit; Empirical bayes; Cost-benefi

Why drivers start drinking and driving--a prospective study over a 6-year period in the GAZEL cohort.

International audienceAIMS: To estimate the frequency with which a group of formerly safe drivers adopt driving while alcohol-intoxicated (DWI), and to determine the factors associated with DWI adoption. METHODS: Participants were current employees or recent retirees of the French national electricity and gas company. An annual cohort questionnaire that includes two questions about overall alcohol consumption is sent each year to participants. A Driving Behaviour and Road Safety (DBRS) questionnaire was administered in 2001, 2004 and 2007. Only drivers who participated in the 2001 survey received the 2004 and 2007 questionnaires. RESULTS: More than 462 participants ceased DWI between 2001 and 2007, while 511 adopted this behaviour for the first time. Multivariate analysis showed that the risk of adopting DWI was associated with male gender and with several changes over the preceding years: increased alcohol consumption, increased number of close friends, decreased number of close relatives and decreased attitudes in favour of strict enforcement/regulations. CONCLUSION: A large number of offenders stopped DWI between 2001 and 2007, concomitantly with an increased crackdown on road violations in France. But this success was compromised by the occurrence of new drunk drivers. Preventive strategies should target factors that facilitate DWI adoption-in particular, increased alcohol consumption and low acceptance of law enforcement initiatives

Serious Injuries: An Additional Indicator to Fatalities for Road Safety Benchmarking

Objectives: Almost all of the current road safety benchmarking studies focus entirely on fatalities, which, however, represent only one measure of the magnitude of the road safety problem. The main objective of this article was to investigate the possibility of including the number of serious injuries in addition to the number of fatalities for road safety benchmarking and to further illuminate its impact on the countries' rankings. Methods: We introduced the technique of data envelopment analysis (DEA) to the road safety domain and developed a DEA-based road safety model (DEA-RS) in this study. Moreover, we outlined different types of possible weight restrictions and adopted 2 of them to indicate the relationship between road fatalities and serious injuries for the sake of rational benchmarking. One was a relative weight restriction based on the information of their shadow price, and the other was a virtual weight restriction using a priori knowledge about the importance level of these 2 aspects. Results: By computing the most optimal road safety risk scores of 10 European countries based on the different models, we found that United Kingdom was the only best-performing country no matter which model was utilized. However, countries such as The Netherlands, Sweden, and Switzerland were no longer best-performing when the serious injuries were integrated. On the contrary, Spain, which ranked almost at the bottom among all of the countries when only the number of road fatalities was considered, became a relatively well-performing country when integrating its number of serious injuries in the evaluation. In general, no matter whether the country's road safety ranking was improved or deteriorated, most of the countries achieved a higher risk score when the number of serious injuries was included, which implied that compared to the road fatalities, more policy attention has to be paid to improve the situation of serious injuries in most countries. Conclusions: Given the importance of considering the serious injuries in addition to the fatalities for international benchmarking of road safety, the proposed model (i.e., the DEA-RS model with weight restrictions) turned out to be effective in deriving reasonable results. We are thereby also inspired to apply this kind of model to a more complete road safety benchmarking practice in the future when the data on, for example, the number of slight injuries, the degree of property damage, and the number of crashes are ready (i.e., comparable) to use.road safety benchmarking; fatalities; serious injuries; data envelopment analysis; weight restrictions; country rankin