This article compares per-mile risks posed by motor traffic to pedestrians and cyclists on urban major and minor roads. Carrying out new analysis of police injury data from 2005-15, the paper finds that per billion vehicle miles, motor vehicles on minor roads create more pedestrian casualties than motor vehicles on major roads. Specifically, for KSI (killed or seriously injured) injuries the rate per billion motor vehicle miles is 17% higher on minor roads (47 versus 40 KSIs per billion vehicle miles), while for slight injuries it is 66% higher (188 vs. 123 slight injuries per billion vehicle miles). Examining the costs of injuries sustained, these are 7.4% higher for pedestrians per motor vehicle mile travelled on urban minor roads, compared to major roads. For cyclists, injury costs are slightly higher (4.2%) on major roads per mile driven, compared to minor roads. These results suggest that re-routing motor traffic to major roads in urban areas may reduce pedestrian casualties. However, if cyclist safety on major roads is not improved, shifting motor traffic from minor to major roads may result in unintended negative injury consequences for cyclists.