How does hourly variation in exposure to cyclists and motorised vehicles affect cyclist safety? A case study from a Dutch cycling capital

Cycling is promoted as a sustainable and healthy mode of transport, which results in an increase in bicycle use in urban areas. Increasing bicycle use comes with growing concerns about cyclist safety. This study examines how the temporal variation in the network-wide exposure to cyclists and motorised vehicles affects bicycle crash frequency. Network-wide hourly volumes of cyclists and motorised vehicles were estimated and regression models were used to identify the effect of the exposure to traffic on bicycle crashes in the city of Utrecht, a Dutch cycling capital. The results show that increasing exposure to motorised vehicles, and to a lesser extent, exposure to cyclists, increases the number of bicycle crashes on 50 km/h roads. For 30 km/h roads, no statistically significant relationship between the exposure to cyclists and bicycle crashes was found. Moreover, it was shown that cyclist crash numbers on 30 km/h roads are less sensitive to an increase in the exposure to motorised vehicles compared to cyclist crash numbers on 50 km/h roads. Furthermore, the exposure to motorised vehicles is a stronger factor affecting the increase in bicycle crashes on roads with bicycle lanes or mixed traffic conditions than on roads with separated bicycle facilities. To conclude, this study shows that road safety for cyclists needs further improvements, as cycling in cities keeps increasing.