Road safety and bicycle usage impacts of unbundling vehicular and cycle traffic in Dutch urban networks

Abstract

Bicycle-motor vehicle crashes are concentrated along distributor roads where cyclists are exposed to greater volumes of high-speed motorists than they would experience on access roads. This study examined the road safety impact of network-level separation of vehicular and cycle traffic in Dutch urban networks, a strategy for which the term ‘unbundling’ is used. Unbundling vehicular traffic and cycle traffic in an urban network is operationalized as the degree to which cyclists use access roads and grade-separated intersections to cross distributors. The effect on the share of cycling in the modal split is also assessed as unbundling may affect the competitiveness of cycling compared to driving in terms of trip length. The analyses were conducted on Dutch municipalities with more than 50,000 inhabitants. Negative binomial regression was used to analyse the effect on the number of police-reported cyclist deaths and in-patients in bicycle-motor vehicle crashes. A mediation model was tested, with Structural Equation Modelling hypothesizing that unbundling corresponds positively with the cycling modal share via the length of car trips divided by those by bicycle. The results of this study suggest that unbundling improves cycling safety, and increases the share of cycling in the modal split. We recommend unbundling vehicular and bicycle traffic in urban networks, e.g. establishing large traffic-calmed areas with short cuts and standalone paths for cyclists (and pedestrians) and, where feasible, grade-separated intersections such as bicycle tunnels.