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Placing Sharrows Outside the Door Zone

Sharrows of Wallingford

There’s a lot of discussion in engineering circles about the proper placement of the Shared Lane Marking, or Sharrow.  I’m a big fan of this pavement marking, but I think it is often poorly applied on many roadways.  This post will discuss the purpose of these markings and how they should be placed on roadways.

The 2009 Federal MUTCD gives five purposes for the Shared Lane Marking, one of which is the following:

  1. 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

fig9c_09_Shared_Lane_Marking

One of the primary purposes of the Sharrow is to encourage cyclists to ride further away from parked vehicles than they might otherwise ride to keep them out of the “door zone.”  The 2009 Federal MUTCD provides the following guidance (recommendations) about the placement of Sharrows next to parked vehicles:

If used in a shared lane with on-street parallel parking, Shared Lane Markings should be placed so that the centers of the markings are at least 11 feet from the face of the curb, or from the edge of the pavement where there is no curb.

QUESTION: Will placing the Shared Lane Markings 11′ from the curb encourage cyclists to ride outside the door zone?

This study prepared for the San Francisco Department of Parking and Traffic suggests that while the 11′ placement of  Sharrows helped cyclists ride further from parked vehicles than cyclists on roadways without Sharrows, the 11′ placement did not convince cyclists to ride outside the door zone.  Figure 5 from the same report suggests that with an 11′ Sharrow placement, cyclists positioned their tires only 2’8″ from parked vehicles – still well within the door zone.

As an engineer, I generally recommend the Shared Lane Markings be placed more than 11 feet from the curb.  The MUTCD guidelines should be interpreted quite literally – the 11 feet guideline is a minimum, and engineers should use their best judgement in determining if additional distance is necessary.  Cyclists should be encouraged to ride as far left as necessary to ensure not only that they don’t hit an opening car door, but also to ensure that they are confident enough in their lane position that they do not instinctively swerve left to avoid an opening car door – even if they would have had sufficient room had they not swerved.  In my personal cycling experience, I begin to be confident enough in my lane position that I know I won’t instinctively swerve when I am at least 5′ or 6′ from parked vehicles – which suggests a minimum sharrow placement of 12′ or 13′ from curb.

Of course, there are other questions that remain to be answered, most notably: will marking Sharrows 13′ from the curb actually result in cyclists riding 13′ from the curb?

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