The safety effect of exchanging car mobility for bicycle mobility
Summary: This report describes the analysis of the effect of exchanging passenger car mobility for bicycle mobility on the number of fatalities and serious road injuries in the Netherlands. A precise calculation of this effect is not possible due to a lack of information, but we were able to give a first and rough approximation of the safety effect.
The analysis considers a substitution of 10% of car trips shorter than 7.5 km by bicycle trips. The analysis is done ceteris paribus, thus, all relevant parameters are assumed to remain equal (except of course mobility). Assuming that the increase in bicycle trips is distributed equally over the network, time of day etc., as current bicycle mobility is, the increase in the number of fatalities and serious road injuries in crashes involving bicycles can be estimated. In the same way, the decrease in the number of fatalities and serious road injuries in crashes involving cars is estimated, assuming that the mobility decrease has the same safety properties as the remaining car mobility.
Firstly, the amount of mobility exchanged (short trips) is calculated, and then expressed as a percentage-change in the total mobility (all trips) of cars and bicycles. Secondly, the effect of extra bicycle mobility on crashes involving bicycles is calculated. The same is done for crashes involving cars. These calculations are disaggregated by age and gender of the driver, because risks strongly correlate with driver age and gender, both for car drivers and bicycle riders.
The results of the procedure described above show, by age group,
the net gain or loss in road safety, related to the mobility
exchange. For each driver age group, the increase or decrease in
the number of fatalities and serious
road injuries is calculated. For hospitalized cyclists in a single vehicle crash we only consider casualties with an injury severity of at least 2 on the internationally used Maximum Abbreviated Injury Scale.
Based on the assumptions given, the calculations suggest an annual increase of 4 to 8 fatalities and of approximately 500 serious road injuries, when 10% of the short car trips are exchanged for bicycle trips for all ages. Further, the results indicate that the number of fatalities decreases if young car drivers (<35 years) switch to bicycles, but when older car drivers do the same, this increases the number of fatalities. The number of serious road injuries increases for practically all ages due to the car-bicycle mobility shift. Only for 18- and 19-year-old males, it is beneficial to switch to cycling. The overall increase is a consequence of the very large number of cyclists that are treated in hospital as a consequence of a single vehicle crash with a bicycle.
Source: R-2010-18 / The safety effect of exchanging car mobility for bicycle mobility - Substituting a small number of short car trips with bicycle trips / Henk Stipdonk & Martine Reurings / Leidschendam, 2010 / SWOV Institute for Road Safety Research, The Netherlands am 20.10.2010