Originally developed by traffic engineer James Mackay in 1993 for the city of Denver, what has since become known as a “sharrow” (shared lane marking on streets) was a compromise from the start.
At the time, the city was unwilling to consider more bike-friendly lane solutions but game to consider a low-cost and easily implemented symbol. Case studies in the decades since, however, suggest that these well-intended markers could be doing more harm than good.
Featuring an abstracted cyclist inside an arrow, the original design came to be known as “bike in the house.” It was meant to point cyclists in the direction of traffic and encourage vehicles to share the road.
The more recent dual-chevron variant was named “sharrow” (a portmanteau of share and arrow) by Oliver Gajda of the City and County of San Francisco Bicycle Program. Perceived success in California led to these icons being deployed around the country, even finding their way periodically onto major highways (as shown above).
Sharrows have been shown to work well on some metrics according to studies commissioned by the Federal Highway Administration. The markings help get drivers outside of the dangerous “door zone” alongside parked cars, increase separation between moving cyclists and motorists and reduce wrong-way cycling on roads. In theory, these symbols also raise drivers’ awareness of bikers sharing their lane.
At least one study, however, concluded that sharrows did less to reduce collision-related injuries for cyclists on the streets of Chicago than either bike lanes or a complete absence of infrastructural intervention. Of course, this could be a city-specific result.
Some cities are still making the case that there is room on the roads for sharrows, at least with some improvements in place. Boston, for instance, has tested out what one reporter dubbed “sharrows on steroids” — basically sharrows reinforced with dotted lines within a wider vehicular lane — which may perform better. Meanwhile in Oakland, solid green paint has been deployed in places to indicate shared lanes, adding more visibility than periodic sharrow markings.
Perhaps these enhanced solutions will prove more effective. For now, though, sharrows alone are still too often used as an excuse to do less rather than more for urban cyclists. Cities committed to public safety also have a working model to draw upon: dedicated (especially separated) lanes for bicycle traffic have a long track record of success.