Sharrows: Shared Lane Markings for Street Cyclists May Hurt More than Help

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.

Sharrow near beautiful downtown Oakland, California, image by Kurt Kohlstedt

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).

Three-way sharrow on residential road by Eric Fisher (CC BY 2.0)

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.

Shared lane marked with sharrows and green paint in Oakland, California

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.

Comments (4)

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  1. Reilly Williamson

    The bright green does help with visibly, but in a wet or raining situation it also reduces friction. On more than one occasion I’ve almost slammed into something because a car swerved into the lane and my bike started hydroplaning

    1. JPB

      Bikes don’t hydroplane. The round profile and high pressure just doesn’t allow a layer of water to build up underneath the tire. The paint is simply slick and the water acts as a lubricant making it more slippery.

  2. Tom Breit

    I’m a lifelong bike commuter in Seattle. We have had sharrows here for a couple of years. To me, they seem confusing at best – a traffic symbol is supposed to communicate information (stop, yield, watch for deer) and not make a vehicle operator wonder what they’re supposed to do. Does that mean bikes have the right of way? Does it mean that the driver should just be aware of bikes? Does it mean that there’s now a “war on cars?” (That’s not a joke, it’s a regular claim in the Seattle Times comment pages.) And that illustration of the bike with the arrows pointing three different ways – what the hell is that supposed to mean? Bikes can go any direction they want including over the curbs? Or, “cyclists be crazy, who knows what they might do!”

  3. Sean

    “At least one study, however, concluded that sharrows did less to reduce collision-related injuries for cyclists on the streets of Chicago ”

    We have too many dumb-asses in Chicago that on one hand want to be treated like cars and ride directly in lanes (which I’m glad for them to be more visible) but then do not obey traffic signals, run stop signs and hang turns without stopping. You can’t have it both ways. I don’t need my car kicked when I pass you for riding like an asshole.

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