In 2009, the Federal Highway Administration approved the use of Shared Roadway Markings ("Sharrows") in their Manual on Uniform Traffic Control Devices (MUTCD). Many cities around the country are using sharrows on streets that are both popular with bicyclists but may be too narrow for conventional bike lanes.
The overall goals are: to improve the position of bicyclists on roads without bike lanes, reduce bicycling on sidewalks, assist bicyclists with lateral positioning in a shared lane with on street parallel parking in order to reduce the chance of a bicyclist's impacting the open door of a parked vehicle, encourage safe passing of bicyclists by motorists, and reduce the incidence of wrong-way bicycling.