Safety in numbers for cyclists-conclusions from a multidisciplinary study of seasonal change in interplay and conflicts.

In many European countries, it is a political goal that future growth in local travel should be absorbed by sustainable transport modes. Concerns that increased walking and cycling produce more accidents have been countered by the "safety in numbers" (SiN) argument. According to SiN, the more walkers/cyclists there are in a population, the lower their risk. SiN has been demonstrated in cross sectional and longitudinal studies, but the mechanisms behind the effect have yet to be proven. Previous studies have mostly relied on register data. The current study, carried out in 2013 and 2014 tests the existence of this effect in a more controlled manner. This is achieved through the use of three data sets: (1) roadside survey data with cyclists, pedestrians and car drivers from Oslo carried out at three time points in the cycling season (2) a panel study covering the same time period, and (3) video observations at four different locations in Oslo. By exploiting the natural seasonal variation in cycling frequency, and by using a repeated measures design we can further control for other factors suggested to lie behind the SiN mechanism, such as differences in infrastructure and traffic culture. The results suggest that bicyclists experience a short term Safety in Numbers effect through the season. Each individual cyclist experiences fewer occasions of being overlooked by cars and fewer safety critical situations (near-misses). Video observation data confirm this pattern. However, the SiN effect seems to be countered by another mechanism taking place at the same time: the influx of inexperienced and risk-taking cyclists through the season. Thus car drivers and pedestrians also report to find themselves being surprised by cyclists in traffic late in the season.