Replacing motorised transport with active travel, such as walking or cycling for transport, has multiple environmental and health co-benefits. However, with the large variety of intervention forms that may be implemented to shift population levels of active travel, such as modifying the built environment or implementing policies that restrict the use of motorised vehicles, it is difficult to know which should be prioritised. It is thus important to understand which types of interventions are most effective at encouraging active travel uptake. This includes identifying whether there are mechanisms or underlying processes common to successful active travel interventions (i.e., intervention functions), or whether differences in intervention design or the specific components included (i.e., intervention form) can influence intervention effectiveness. Thus, this thesis aims to identify, evaluate, and understand the key characteristics of effective interventions to encourage shifts towards active travel.

The first part of my research involves a systematic review comparing the effectiveness of carrot, stick, and a combination of the two, or carrot-and-stick transport interventions. Interventions with a stick strategy, such as those with functions involving taking away road space or leading to decreases in convenience, are less widely assessed in the literature compared to those with a carrot strategy, such as those aiming to increase access and safety for active travel. The findings also suggest that stick and carrot-and-stick interventions are more effective at either reducing driving or increasing active travel than carrot-only interventions. I also find that interventions seeking to influence driving behaviour using financial means or active travel by modifying access, safety, and space are more impactful than others.

Having identified that there is a need to increase the evidence base on interventions that include a stick strategy, I evaluate three interventions with stick or carrot-and-stick strategies. The first is a study evaluating the London Ultra Low Emission Zone, an area-based vehicle charging scheme. I use data from the Children’s Health in London and Luton study, a parallel cohort study of primary school children. Children living further from school and exposed to the intervention had a higher likelihood to switch from inactive to active modes of travelling to school than those who were unexposed. The second evaluation study examines the introduction of low traffic neighbourhoods (LTNs) in Southwark, London. LTNs use physical barriers to restrict traffic from passing through residential streets while allowing pedestrians and cyclists to access the street. Moreover, other minor streetscape improvements to pedestrian infrastructure were made, and altogether, the interventions constitute carrot-and-stick strategies. Findings reveal that while traffic volumes and speeds decreased in some of the neighbourhoods, there were no corresponding increases in walking and cycling.

The third evaluation study involves investigating an intervention with carrot and carrot-and-stick strategies. I use interrupted times series analyses of routinely collected cycle count data to assess how cycling levels changed following cycle lane expansions in Paris and Lyon in France. Although there were no discernible level or trend changes in cycling counts, cycling increased more in Paris compared to Lyon. Given that various cycling infrastructure designs were introduced in both cities, the final study explores how to advance our understanding of whether differences in cycling infrastructure design can influence intervention effectiveness. I develop a virtual street audit using Google Street View to characterise infrastructural changes made due to the French cycling lane interventions, from which I derive function scores. I find that cycling infrastructure forms that involves stick strategies, such as taking traffic lanes and parking space from drivers, have the highest associations with increases in cycling levels. Correspondingly, functions aiming to increase safety or space were found to be among the most impactful.

This thesis adds to the literature by not only identifying common characteristics of effective active travel interventions, such as whether it includes a stick strategy, but also finding that these are relatively under-represented in the literature. My findings also suggest there may be a hierarchy of active travel needs that may be important to address when developing interventions, such as increasing safety and space for pedestrians and cyclists. To further increase intervention effectiveness, the intervention form, or the way interventions are designed and implemented, should align with their core functions and adapted based on individual contexts. Further research is needed taking consideration of intervention form, function, and contextual factors into account to strengthen and inform public health policy and practice.