Gaps in the evidence base

There is little literature that looks at how cycling infrastructure and schemes affect people with disabilities, with the exception of some looking at the negative effect of shared spaces. For example, Clayton (2016) calls for more research on how much of an obstacle cycling infrastructure is to people with disabilities (e.g. bollards) and if there is an optimal way to mitigate this. Additionally, no literature was found on how the loss of parking from cycling infrastructure, narrow paths and/or mixed space around bus stops affects those with disabilities.

The Department for Transport (2016) also points out that that there appears to be a relative shortfall in evidence about how different groups in society – e.g. by demographic or health status– respond to different interventions. Evidence of change tends to be based on an aggregate level rather than differentiating for subgroups.

While the literature does point out what good investments decisions are, such as a mix of revenue/capital and segregated cycle paths where possible, it does not answer what the optimal mix of investments are. Both the Department for Transport (2016) and Pucher, et al. (2010) acknowledge that there is a gap in knowledge as to what mix of infrastructure is optimal, and suggest that in actual fact the optimal mix might vary between different circumstances. As such tailoring the interventions to local circumstances rather than trying to achieve a certain mix would be the most beneficial approach.

The expected effects of the policy interventions are also not fully known given their success depends on local circumstances. Hence, it is difficult to scale these effects to a national level which is why little evidence exists.

The National Institute for Health and Care Excellence (NICE, 2012) compiled their own list of gaps in the literature which are still relevant today.

• Lack of evidence on whether or not interventions to increase walking or cycling for transport or leisure result in a decrease or increase in participation in other types of physical activity.
• Lack of evidence on whether people who cycle or walk for recreational purposes, eventually adopt it as a form of transport.
• Lack of UK evidence on whether differences in urban and rural settings and environments impact on the implementation and effectiveness of interventions to increase walking or cycling.
• Lack of evidence on the barriers to, and facilitators for, inter-sector and inter-agency collaboration to promote walking and cycling. Barriers may include the working cultures of different professionals.
• Lack of UK evidence on the extent to which the provision of a free bus service impacts on walking levels.

Lack of UK evidence on the impact that an individual's perception of distance has on their view of how viable cycling or walking is as a mode of transport. There is also a lack of evidence on what interventions can effectively change someone's perception of distance as a barrier to walking and cycling.