Sharrow / Shared lane marking (SLM)

Sharrow on downhill side of a Seattle street

For the latest from the 2009 MUTCD and sharrows/SLM/BMUFL (bikes may use full lane); see bicycles-may-use-full-lane-slm-mutcd-updates …

A marking that has gained some attention lately is the so-called Sharrow (a contraction of the words shared and arrow), more technically named a Shared Lane Marking (SLM). They are currently not part of the MUTCD and as such their use is still considered “experimental” which means any use of them requires a wavier. I am not aware of any usage anywhere in Arizona — if you know of any please leave a comment or email me a pic. Their use was suggested as a possible mitigation of the light-rail-bike-lane mess between 7th and 24th street.

The (informal?) home page of the NCUTLO’s Bicycle Technical Committee has the currently proposed technical documentation on SLM.

When used over parking, they are supposed to encourage cyclists to ride outside of the door zone. The spec calls for them to be placed “at least” 11′ from the curbface to the center of the marking. At the same time their placement is supposed to make it clear to overtaking motorists that the lane is not (side-by-side) shareable.

Dan Gutierrez has an excellent set of pictures/diagrams that illustrates that 11′ really isn’t enough.

When used on roads without parking and with a usable space of less than 14′ lane (i.e. not generally sharable side-by-side) they are to be placed no closer than 4′ from curbface to center of marking.

I think they would be far better markings in critical width situations as opposed to using a nonsensical fog stripe (making a fake bike lane) — which is the norm here in suburban Phoenix. Alas, this is not to be, at least under the current proposal, since under “guidance” they may not be placed on roads with posted speed limits above 35mph. Guidance doesn’t mean never, but let’s face it…

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