Background Restrictions of male passengers of motorcycles to prevent homicides is a long-standing policy in Cali, Colombia. For some periods of time, the policy was suspended and then put into action again. All these changes were never evaluated and there has been controversy due to the perception of citizens, specifically motorcycle users, that the law was properly implemented in some periods and poorly applied in others. Our aim was to examine the effect of the non-application of the motorcycle male passenger restriction policy on the risk of homicides in Cali, Colombia.

Methods Ecologic study conducted using an interrupted time series analysis. The main outcome was the aggregated daily counts of homicides. Secondary outcomes were the aggregated daily counts of homicides using a motorcycle and using motorcycle and firearm. Incidence rate ratios (IRR) were obtained by comparing periods of policy implementation with periods of lack of implementation in autoregressive negative binomial regression models.

Results There was an increased risk of homicides when the policy was not implemented (IRR=1.12; 1.05–1.19). There was no effect on the risk of homicides committed in motorcycles (IRR=0.98; 0.88–1.10) and when a motorcycle and firearm were used (IRR=0.99; 0.89–1.10).

Conclusions The lack of implementation of the ban of motorcycle male passengers was associated with an increased risk of homicides. Our findings support the importance of this policy to prevent homicides in Cali, Colombia. Future work should examine how this policy influences other policies related to prevent homicide and violent risk-related behaviour.