A rider wonders what the painted marks mean. (It's a sharrow.)

Shared lane markings and sharrows painted on the road are prominent parts of bicycle infrastructure in most major cities, and sharrows are part of Santa Barbara’s new Bicycle Master Plan with hundreds of thousands of dollars being allocated to new applications. While originally introduced with the best of intentions, recent analyses measuring the collisions in a number of different cities have shown “Share the Road” signage and sharrows have detrimental effects on safety and do not increase bicycle ridership.

The first of these studies, conducted in Vancouver, Canada, found that even when ridership was taken into account, the risk of collisions on roads where cyclists were encouraged to share the road with motor vehicles were no lower than roads without any cycling infrastructure, while risks on roads with cycle lanes, cycle tracks, or no parked cars were significantly lower. A subsequent study conducted in Toronto and Vancouver, Canada, reported a doubling of collisions risk on roads with sharrows, while risk decreased on roads with cycle tracks (physically separated lanes) alongside major streets. Lest one think that the problem with sharing the road is a Canadian one, the most recent study and convincing study “Relative (In)Effectiveness of Bicycle Sharrows on Ridership and Safety Outcomes” was conducted in Chicago. The researchers found that the rate of injuries per 100 bicycle commuters was greater on streets with sharrows than streets no lane markings, while streets with bicycle lanes had even lower rates. Over time, ridership increased sixfold on streets with bike lanes, while the increases on roads with sharrows or no markings was minimal.

How transportation planners “fell” for sharrows is a fascinating story of what can happen when planners can’t get the political buy-in or financing for what they know is best for cyclists.

Sharrows and other shared lane markings were developed as a low-cost method of alerting motorists to the possible presence of cyclists and indicating that the center of the travel lane is the safest position for cyclists on roads where bike lanes were not feasible because of cost or space. When they were introduced in Denver in the early 1990s, it was hoped that they would increase ridership and decrease the collisions due to parked drivers opening a door, motorists passing at unsafe distances, and bicyclists riding the wrong way. As is often the case with road safety innovations, the evaluations on which the approval was based used processes measures (favorable changes in attitudes and behaviors believed associated with safety) rather than the number of bicycle-involved collisions.

One of the first of the process was performed in San Francisco (http://nacto.org/wp-content/uploads/2010/08/San-Franciscos-Shared-Lane-Pavement-Markings-Improving-Bicycle-Safety.pdf). Sharrows successfully increased the distance between cyclists and parked cars, and distance between cyclists and passing vehicles also widened, but did not have a consistent effect on wrong way riders. Another analysis in three cities in the United States found substantial variability in the extent to which cyclist and motorist behavior changed. For example, the proportion of bicyclists riding over the sharrows (the desired effect) increased in two of the three cities but did not change in the third (http://nacto.org/wp-content/uploads/2011/01/Evaluation-of-Shared-Lane-Markings.pdf). Due to the conflicting results in these three cities, the authors concluded that guidance should be improved by applying sharrows only in traffic settings where the results could be evaluated and reported as scientific evidence. Sharrows were finally approved by the Manual of Uniform Traffic Control Devices in 2009.

However, subsequent studies continued to raise doubts about the effectiveness of sharrows. An online survey found that “Bicycles May Use Full Lane” signage was much better understood than sharrows or “Share the Road” signage. Evaluation of a law in Maryland that required motor vehicles to pass bicyclists at a distance of greater than three feet found that motorists were just as likely to pass too closely to cyclists on roads with sharrows as they were on roads with no bicycle markings.

While sharrows may have a place in certain low speed (20 mph) narrow roads where cars cannot pass cyclists, the abundance of data documenting their dangers in higher speed environments led Federal Highway Administration to recommend that sharrows in which green-colored pavement is used as background conspicuity enhancement not be used until more information was analyzed. In order to assure safety while guidance can be improved on this sensitive matter, it may advisable for bicyclists to refrain using roads with sharrows and other shared lane markings and for Santa Barbara planners admit that while the cost of sharrows is low, their benefits in terms of safety may be nil.


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