Comparison between Powered Two-Wheeler and Passenger Car Free-Flow Speeds in Urban Areas

Accident data indicate that motorcyclists are a particularly vulnerable group of road users because they run a higher risk of being injured or killed in an accident than passenger car drivers. One of the countermeasures that can improve traffic safety for motorcyclists is an increase in awareness and knowledge about powered two-wheelers (PTWs) in the planning, construction, operation, and maintenance of new and existing roads. Road design standards and policies that regulate design process and safety evaluations are usually based on passenger car characteristics only. In particular, the passenger car operating speed is used as the critical input for design choices of geometric elements connected with traffic safety and as a performance measure to evaluate road design and consistency. Because the passenger car operating speed might not be representative of the PTW operating speed, this study compared the PTW and passenger car speed distributions in urban areas to establish definitively whether they are similar. The results showed that PTW speeds are always considerably higher than passenger car speeds and that the corresponding operating speeds are correlated. Therefore, a prediction equation to estimate the PTW operating speed starting from passenger car operating speed was developed for urban streets. This equation can help highway engineers to estimate expected PTW speeds that can be effectively used in the safety evaluations of new and existing roads where the significant presence of PTWs in the traffic flow suggests that this vehicle type should be considered.