It’s essentially a bike lane symbol with two chevrons above it that is usually installed on streets too narrow or uncongested for conventional, dedicated bike lanes. San Francisco, Seattle, Portland, New York City, and Baltimore are just a few of the cities that have specified them in their master bicycle plans or experimented with them. Acceptance of sharrows grew quickly and they have been included in the most recent edition of the federal Manual on Uniform Traffic Control Devices (MUTCD).
Sharrows are a relatively recent innovation in bicycle facility design intended to help cyclists assert their right to the road and to encourage riders to stay out of the “door zone”—the area next to parked cars in which car doors swing open and sometimes cause significant harm to cyclists. Sharrows are usually installed about four feet from the side of parked cars, indicating where cyclists should position themselves in the road. Sharrows also help to reduce wrong-way riding by cyclists. In cities with narrow streets, like Philadelphia, sharrows can have a traffic-calming effect by urging drivers to be considerate and “share the road.”