Cycling is widely promoted as a healthy and sustainable means of transport. At the same time, traffic safety concerns are growing, both in the Netherlands and elsewhere, because of increasing numbers of cyclists involved in crashes (fatal and serious injury). Scientific evidence could help identify infrastructural factors affecting these crashes, which requires research results on different aspects of this issue to be reviewed.
In this review, we focus on different aspects of cycling infrastructure and their contribution to the risk of bicycle crashes. Dutch and international studies are reviewed that address a bicycle crash risk indicator as an outcome measure, thereby controlling for differences in cyclist flow. Controlling for cyclist flow is crucial for valid interpretation of the safety levels of infrastructure elements or designs. This requirement limits the number of relevant studies, because in many studies cycling flow is unknown and only crash frequency (not crash risk) is reported.
A distinction is made between findings from Dutch studies and international studies (not conducted in the Netherlands). This was considered necessary because of the ‘advanced’ cycling culture and infrastructure facilities for cyclists in the Netherlands. In some instances, it appears that this distinction results in different outcomes. These are mentioned in the report.
First of all, the conclusions of the review focus on the safety enhancing features of the cycling infrastructure that are to some extent evidence-based, followed by the features about which we still have no evidence.
The evidence for infrastructure features that affect safety is generally based on a limited number of studies, conducted on specific locations in different geographical settings. This implies that the results may not be interpreted as valid for every specific location, because local circumstances may differ from those included in the studies. As the number of studies increases, providing consistent evidence on different locations, the generalisability of the outcomes will be stronger.
For each of the different infrastructural elements, the main findings are listed below:
Urban versus rural areas
In urban areas, the number of crashes involving cyclists is higher than in rural areas. Dutch figures show that over 60% of fatalities and about 81% of serious injuries (involving motorised traffic) among cyclists are due to crashes in urban areas. Figures from other countries support this general conclusion with sometimes different proportions.
Network route choice
Dutch cyclists prefer routes with bicycle facilities, low speed limits, low motorised traffic volume, good surface quality and short travel time. International studies found comparable results and point to additional preference factors, i.e. light conditions.
There is growing evidence for improved safety as a result of implementing bicycle tracks compared to bicycle lanes, or no facilities for cyclists. Recent Dutch studies do not show safety effects of bicycle lanes compared to no bicycle facility. However, some relatively recent international studies show that bicycle lanes do improve safety compared to no bicycle facility.
If we consider intersection safety, two-way bicycle tracks are found to be less safe than one-way bicycle tracks.
Because this perspective addresses quite specific features, only few studies focus on them, and evidence is still based on a very limited number of studies. We found indications for the following features affecting safety:
- Wider bicycle tracks improve safety.
- On-street parking decreases bicycle safety.
- Tram tracks on the road decrease bicycle safety.
- Presence of obstacles such as poles, trees, and signs within two meters of the bicycle facility decreases cycling safety
- Presence of road lighting increases cycling safety
A general finding is that, for cyclists, intersections are more dangerous than road sections. Concerning intersection safety we found that:
- Intersections with lower speed limits are safer.
- Bicycle crash risk is reduced when the bicycle crossing at the intersection is deflected further away.
Relating to the safety of roundabouts, Dutch and international studies have contrary results. In the Netherlands, bicycle crash risk at roundabouts is lower than at intersections. However, international studies show that roundabouts increase the risk of a bicycle crash compared to intersections. Concerning intersection safety we found that:
- Roundabouts with bicycle tracks are safer than roundabouts with bicycle lanes or roundabouts without any bicycle facility.
- Two-lane roundabouts increase the risk of a bicycle crash.
- Higher speed limits at roundabouts decrease bicycle safety.
- Roundabouts are safer when vehicles have priority.
We identified a number of relevant infrastructure features for which no cycling safety evidence was found in the literature. These are listed below.
- Location data for seriously injured cyclists not involving motorised traffic were not found.
- No information was found on bicycle crash risk in urban versus rural areas.
- No safety risk indications were found for shared space with pedestrians and solitary bicycle tracks.
- On the issues of kerbs and surface condition no studies addressing crash risk were found.
- No risk-based evidence was found that bicycle boxes and dedicated green phases at intersections improve cycling safety.
The general conclusion of this review is that there is a growing body of evidence that several infrastructure features relate to cycling safety, but that the evidence is still based on a limited number of studies, that it only concerns crash frequency (not risk), and does not cover all relevant features. The need for more studies is not only prompted by the lack of knowledge as such, but more importantly by the growing concern about the increasing number of crashes involving cyclists.