Placing hourly variation in bicycle volume and crashes in the bigger perspective of road safety for cyclists in Dutch cities

While bicycle levels in Dutch cities increased rapidly the last few years, it is still debatable what the effects of increasing bicycle volumes are on road safety. On the one hand, a safety-in-numbers effect exists, meaning that increasing cycling levels lead to a less increasing risk for cyclists. On the other hand, recent studies found a hazard-in-numbers effect, revealing that more cyclists on the road leads to a large increase in serious bicycle crashes and a slight increase in bicycle fatalities. A forthcoming study by the author contributes to this debate by investigating the effect of hourly variation in bicycle and motorised traffic volume on bicycle crashes related to type of bicycle facility. But why is hourly variaton in bicycle traffic so important to investigate road safety for cyclists in Dutch cities, the author’s PhD topic? This is discussed in the present paper. Broadly speaking, most studies related to bicycle crash risk make use of the average annual daily bicyclists and the average annual daily traffic to predict bicycle crashes, barring additional factors. This is very helpful to understand the effects of bicycle volume and motorised traffic volume on road safety for cyclists. However, such analyses do not grasp the temporal variation in daily bicycle volume, daily traffic volume and bicycle crashes. To analyse varying loads of the road network at different times of the day, and how this relates to road safety for cyclists more detailed bicycle and traffic volume data must be used. The present paper discusses how this could help for bicycle safety studies in Dutch cities, by evaluating the usefulness of hourly bicycle and traffic count data from count stations in a mature cycling city in the Netherlands.