Geometric and operational determinants of motor vehicle-bicycle overtaking on Brazilian urban roads

OBJECTIVE: Overtaking maneuvers between motor vehicles and bicycles (OVB) represent a critical hazard for cyclists due to required lateral clearances and vehicle speeds. This study aims to evaluate the OVB process in urban environments, focusing on the main geometric and operational attributes that influence cyclists' objective road safety indicators. METHODS: A quasi-naturalistic observational study was conducted on urban roads in Fortaleza, Brazil, using an instrumented bicycle. Data on vehicle speed, lateral passing distance, lane configuration, vehicle type, and the presence of adjacent traffic were collected across 1,075 overtaking maneuvers. Statistical analyses were performed to assess the impact of these attributes on safety indicators. RESULTS: Analysis revealed that 76% of observed passing maneuvers violated the Brazilian national recommendation of maintaining a minimum lateral distance of 1.50 m. The presence of cycling infrastructure and the absence of traffic in adjacent lanes were significantly associated with greater passing distances. Furthermore, a behavioral compensatory threshold was identified at a 0.85-meter lateral distance: drivers modulated speed as a risk-mitigation mechanism only during critical clearances, whereas no speed adjustments were observed at the 1.50-meter legal threshold. CONCLUSIONS: A vast majority of drivers fail to comply with recommended passing distances, highlighting the need for targeted infrastructure and operational interventions. The existence of dedicated cycling facilities effectively improves lateral separation. Moreover, drivers adapt speed only under extreme proximity (under 0.85 m), demonstrating that legal limits alone do not induce safer driver behavior without structural or physical support.