Sunday, November 11, 2007

How Wide is a "Share-able" Lane?

Keri from Orlando wrote:

Where do you ride if you are in a lane that is just wide enough for a car to squeeze past you within the lane when you ride ~3 feet from the curb? I'm struggling with this one. I don't want them to squeeze past me within the lane. I don't want to ride closer to the curb. Would this lane width be less than 14 feet?

The two key questions here are "How wide must a lane be to be "share-able?" and "How far from the curb/edge should I be if it is?"

Many states have statutes allowing bicyclists to leave the right-hand side of the lane if the lane is too narrow to share with another vehicle, but none of them define just how wide such a lane would be. The Florida Department of Transportation actually did define that in their standards: 14 feet. But that doesn't officially (statutorily) define a 14-foot lane as wide enough to share. Still, I think it's a reasonable width; it's based on cyclist needs, safe passing, standard vehicle widths, and sound reasoning.

Of course you're not going to stop and pull out a tape measure to figure out if the lane is wide enough to share. Instead, just look at a car ahead of you in the lane and ask yourself if there is enough width left over from the vehicle for you to operate safely. If the answer is No, then move left into the lane.

Keri doesn't want to ride "less than 3 feet from the curb," but lane widths are measured from the lane stripe to the edge of the pavement, not to the curb, so a 14-foot lane would be 15.5 feet if measured to the curb face. On most modern streets in Florida, the gutterpan is about 18 inches wide, so if you ride about 18 inches left from the seam of the asphalt and the gutterpan you'll be about 3 feet from the curb face.

Moving inward from the curb face: 18 inches of gutterpan + 18 inches to the cyclist's wheeltrack + 18-24 inches to the left shoulder of the cyclist + 3 feet of safe passing space = 7.5 to 8 feet. That would leave 8 to 8.5 feet of space for the passing motor vehicle. Standard-size cars are about 5.5 feet; full-size SUVs and vans about 7 feet; large trucks and buses 8.5 feet.

I think 18 inches is sufficient distance to ride from the gutterpan seam, usually giving you enough maneuvering room to deal with debris and crosswinds. Potholes are another matter.

If the lane is less than 14 feet, you're justified in moving farther left. Unfortunately, most motorists don't see it that way. They usually see a 12-foot lane as wide enough to share.


Donny said...

Good analysis, but I have to say I disagree with your final comments. Most motorists don't see a lane as share-able at all and believe that bicycles don't have a right to use the road in the first place. Even when there is a bike lane. >_<

Keri said...

Thanks Mighk! Great explanation. The illustrations are very helpful too.

Regardless of whether or not they WANT to share it, a higher percentage of motorists recognize that a 9 or 10 foot lane is not share-able because they can visualize it. I find that most motorists pass safely without comment when I take a narrow lane.

As Mighk says, that perception does change as the lane width increases. A lot of roads seem to have that ambiguous width that motorists visualize as share-able, but would be unsafe or uncomfortable for us to share.

It's helpful to recognize that we do have a right to take that lane! To borrow from a recent FBA blog post ( “I'm good enough, I'm smart enough, and doggone it, I deserve to be passed safely!”


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