Road work zone accident studies

The primary objective of this task, part of the ARROWS project, is to draw conclusions about the nature and extent of work zone traffic accidents. Tothat end, we collected and reviewed existing empirical studies concerning work zone traffic accidents, as well as literature reviews of such. We focused on a number of relevant work zone and work zone accident characteristics. E.g.: -type of road; -type and duration of works; -interaction between works and road; -weather; and -time of day. In addition, we attempted to draw conclusions about trends over time, effectiveness of safety devices, and national differences. Drawing conclusions was hampered by a dearth of studies with sufficient sample sizes and adequate use of statistical techniques. Questions can also be raised about the adequacy of data collection procedures. In addition, results from different (even adequately done) studies were often contradictory and/or confusing. Nevertheless, a number of (tentative) conclusions may be drawn. First of all, accident rates in work zones are higher than in similar, non-work zone situations. In addition, work zone accidents typically account for several percent of all accidents. It turns out, however, to be quite difficult to estimate exactly how unsafe work zones actually are. Estimates vary widely, and a meta-analysis could be profitably done. The relative severity of work zone accidents is also difficult to determine. Secondly, work zone accidents are mainly often associated with fair weather and daylight conditions. Rear- end accidents seem to be especially common. There may also be an interaction between accident severity, time of day, type of area, traffic density, and type of accident. This possibility should be further investigated. Thirdly, there is quite likely some structure in intra-work zone accident rates. However, this could not be irrefutably established. Sections ‘after' a work zone are, in any case, not substantially more dangerous than a normal road section. Fourth of all, work zones on the side of the road do not necessarily have any negative safety impact. Work zone of shorter duration might have a higher accident risk, yet the evidence is not airtight. Work zones in the neighborhood of entrance ramps may also have higher accident rates, but the results are mixed, even within the same study. In addition, work zones using full contraflow are often signalled as being relatively dangerous, but the results are mixed. Fifthly, different types of roads, with and without work zones, have different accident rates. However, we could not clearly establish a differential safety effect. Sixth of all, no convincing empirical literature concerning accident risks as a function of safety devices was found. Seventh, the role of contributory human factors (as registered in accident statistics) is unclear and contradictory. Finally, no overall temporal trend in work zone accident rates could be clearly established, and we did not dare to draw international comparisons. Overall, the simplest and most robust method for predicting work zone accidents, is to use exposure (e.g., traffic volumes and operational hours) and pre-work zone accident rates. In addition, we feel that international research, with sufficient sample sizes and appropriate use of multivariate statistics, could form a major contribution towards understanding the epidemiology of work zone accidents