Thirty kilometers per hour (30 km/h) speed limits may potentially improve road safety, population
health, active travel, and the liveability of cities. Nevertheless, the implementation of 30km/h speed
limits in cities remains a challenge. Although several European cities have implemented city-wide
30km/h speed limits, the large majority of European cities currently does not have such a city-wide
30km/h policy. Hence, the implementation of 30km/h speed limits in such cities largely depends on
local decision-making tailored to specific streets or neighbourhoods.
Research until now has not comprehensively captured reasons and expected effects for the
implementation of local 30km/h speed limits by local decision-makers. Furthermore, it is unclear to
what extent additional measures (e.g., physical interventions such as speed bumps) are
implemented. Understanding such reasons and expected effects can inform a more policy-relevant
research agenda. For instance, it can elucidate effects expected by local decision-makers that are
understudied by researchers; or shed light on combinations of 30km/h speed limits and additional
measures that are often implemented in practice, but of which the effects are poorly understood.
Furthermore, the comprehensive impact of 30km/h speed limits beyond collisions and casualties, is
understudied, including impact on physical activity, active travel behaviours, neighbourhood
liveability, and air pollution. It is unclear whether potentially positive impacts particularly benefit
vulnerable subgroups in society, such as young children, individuals with a poor health status, or
individuals with a lower socio-economic position.