Photo by NATCO.

People traveling by both bike and automobile have to share the road, but it’s not always clear how they should do that. Some streets have marked, dedicated bike lanes or protected bikeways and others have shared-lane markings, or “sharrows”.

Reader Mike Forster wants to know what bike sharrows are supposed to do and if they are effective:

Do sharrows actually do anything? As a regular cyclist, I don’t see how they’re an improvement, but I’m curious if I’m missing something about their effectiveness. Can someone explain the thinking behind sharrows? Are there studies showing to back that thinking up?

Bike sharrows are road markings used to say that the space is for both bicycles and automobiles. The markings reinforce the legitimacy of bicycle traffic on the street as well as tell bicyclists where in the road they should ride. Sharrows can also be set up to point riders in the right direction along a particular route.

Chris Slatt points toward a great resource on sharrows from the National Association of City Transportation Officials that gives a thorough breakdown of the benefits and typical applications.

3D concept of sharrows. Photo by NATCO.

Sharrows tell everyone that the road they’re on is a bike route. They don’t require additional street space and they cut down on sidewalk riding and bicycling in the wrong direction.

3D concept of sharrows on an urban street. Photo by NATCO.

Sharrows increase the distance between cyclists and parked cars, keeping cyclists out of the “door zone.” Generally, they don’t work as well on streets that have a speed limit of 35 mph or higher.

Matt Johnson adds that sharrows sometimes serve the purpose of guiding cyclists across hazards like streetcar tracks or explicitly denoting bike routes.

Sharrows guiding cyclists across the South Lake Union Streetcar tracks on Westlake Avenue in Seattle. Photo by Matt Johnson.

Sharrows marking “The Wiggle,” a bike route in San Francisco which avoids steep streets by weaving through the street grid. Photo by Matt Johnson.

Sharrows accompanied by bike route signage above the stop sign. Photo by Matt Johnson.

Dan Reed wrote a post last year about the types of roads sharrows work well on.

David Cranor noted research that says sharrows work: there’s an FHWA study showing that they give people on bikes more space both from parked cars and passing drivers, and another another showing that on roads with sharrows, the ratio of of severe injuries to total injuries was lower than on one with no markings.

Do you have a question? Each week, we’ll pose a question to the Greater Greater Washington contributors and post appropriate parts of the discussion. You can suggest questions by emailing Questions about factual topics are most likely to be chosen. Thanks!

Michael Lewis is a native of Montgomery County and currently lives in Olney. He has a BS in Community & Regional Planning from Temple University in Philadelphia. An avid rider of Metrobus and Metrorail, he was formerly a Professional Development Associate at the American Planning Association and an intern at the Housing Opportunities Commission of Montgomery County.