Substituting short car journeys with an active mode of transport has the potential to reduce congestion, air pollution and encourage a healthier lifestyle. However, walking and cycling have a higher risk of road traffic injury than travelling by car. This work attempted to estimate the likely effects on safety of increasing levels of active travel, using National Travel Survey data, and road injury data from the Stats19 database.
Analysis of National Travel Survey data showed that, on average, 12km per person per year has potential to be walked instead of travelled by car (based on trips which are <1km in length). If all of these short car trips were replaced by walking this would represent a 4% increase in walking. Using current levels of risk, it is estimated there would be an additional 406 pedestrian casualties (of all injury severities) if half of the short trips currently carried out by car were replaced with walking.
Analysis of National Travel Survey data showed that 406km per person per year has potential to be cycled instead of completed in a car (based on trips which are 1-8km in length). If all of these short car trips were replaced by cycling this would represent a 473% increase in cycling.
When estimating the change in casualty numbers if these short car trips were replaced with cycling, the analysis first estimated a safety in numbers (SiN) effect where the casualty rate is assumed to reduce with increased cycling.Taking SiN into account, it is estimated that there would be a slight increase in cycling casualties (2,505 of all severities) compared with the current situation. This estimate is based on a modelled relationship between cycling risk and cycle travel which is not necessarily causal; there are other factors not considered which are likely to contribute to different safety levels in different areas. For example, those local authorities which have high levels of cycling and lower cycling risks may also have good cycling infrastructure.
The analysis suggests that the impact of SiN for cyclists is considerable. For comparison, using current levels of risk with no SiN adjustment, it is estimated there would be an additional 41,472 pedal cyclist casualties (of all injury severities) if half of the short trips currently carried out by car were replaced with cycling.
The modelling predicted that alongside the changes in pedestrian and cyclist causalities, there would also be a reduction in car occupant injuries of 2,171 because of fewer people driving. This means that there would be a net increase in casualties overall of 740 (although note that injury severity was not taken into account).
Some authorities have both active travel and road casualty targets. The results show that progressing towards both of these goals simultaneously may be challenging without additional road safety measures. SiN has the potential to act as an enabler for active travel, but there is not currently a standard measure for SiN. In addition, more work is required to fully understand why SiN occurs and how to make design decisions that build it into active travel planning. It is still unclear to what extent SiN occurs naturally, and how much is through careful planning of aspects such as infrastructure and behavioural change interventions. Interventions aimed at encouraging more people to walk or cycle must incorporate measures to improve safety, both to avoid increasing the number of road casualties, and to manage public perception of the risks involved.
Further limitations of the work are that the modelling accounts for factors including mobility issues, age and access to a bicycle, but does not account for characteristics of each trip; for example, the availability of cycle infrastructure or hilliness of the route. The non-included variables may include some which are important factors in mode choice and in risk. The benefits of active travel to health, the environment and congestion, also have not been considered in this analysis.