Influences on lateral passing distance when motor vehicles overtake bicycles

Cyclists are often passed by motor vehicles in low-cycling countries where most riding occurs on roads. When passing events occur, the lateral passing distance (LPD) between motor vehicles and bicycles is critically important for objective and subjective safety. This systematic review identified 42 papers reporting 36 independent studies of LPD. Seven papers reported sufficient information to be included in meta-analyses for four different variables; road width, speed limit, on-road bicycle lanes compared to no bicycle lanes and bus versus car. The meta-analyses showed significant positive relationships between LPD and road width, and between LPD and speed limit; and smaller LPDs when cyclists were passed by buses rather than cars. The effect of on-road bicycle infrastructure was inconsistent. Studies that considered cyclist factors such as gender or type of cyclist showed mixed results. Seven out of eight studies found that the closer the cyclist rode to the kerb, the larger the LPD. Lastly, the passing strategy chosen by drivers (accelerative or flying) also showed mixed results. The results of the review are consistent with the predictions of the Multiple Comfort Zone model which predicts that the distance a driver leaves between their vehicle and other road users will be based on attempting to maintain their own comfort zone. Other motor vehicles pose a greater risk to drivers than bicycles, therefore the distance a driver chooses between their vehicle and a bicycle may be compromised if there are other vehicles present or if the available travel space is restricted. As governments around the world grapple with increasing health costs caused by physical inactivity, bicycle riding is being encouraged. Given the importance of the passing manoeuvre for cyclist safety, when designing infrastructure to foster cycling, factors that influence LPD should be considered.