Wednesday, March 16, 2011

The Twelve Foot lane

This kind of ties back to my post on Boulevardizing the Lowell Connector.

My office park recently sent a scolding email to its residents for walking from the parking lot, over the driveway, up a bankon, and over a fence and into the building.  Aside from us trampling flowers to save 30 seconds on our way into the office, they were worried we were going to get run over in the driveway.

Yes, there is a less than ideal curve and grade in the roadway right before where we cross.  However, this seems silly to me: why are cars going so fast in a driveway, they risk running over adults merely crossing the street?  A car going 20 MPH stops in 20 feet, including reaction time.  That's not much more than a car length.  If a road is so curvy you can't see a car length in front of you - you should be going slower than 20 MPH, and this office park driveway isn't that bad.

My argument was that the road is simply too wide.  That it has lanes the size of an interstate yet is merely a driveway in theory.  People didn't believe me so I broke out the tape measurer:  Yup, twelve-foot lanes.  And then some. Crazy, I said.  Dangerous.

This is the required lane size for an interstate!  Before you say, "hey!  The lanes on an interstate don't seem that wide to me!" Think about this:  The twelve-foot-wide lane can keep your below-average driver in your below-average car within its boundaries at 75 miles per hour.  At 75 mph, any deviation from straight is going to get you in real trouble, real fast.  If the road is narrower, to keep in our lane, we reflexively drive slower.

How wide is your average car?  My Altima isn't even six feet wide.  An F-150 is about 8 feet wide, and a semi might run 9 feet.  While a re-engineered Connector couldn't ban Semis, we also do not want to encourage 75 mph driving, we want to encourage 30 MPH driving.  So the lanes should be narrower by a foot or two a piece.  Added benefit is less road noise and more room for people, bikes, and parking.  The Jeff Speck Report gave the same suggestion for Market Street and other downtown roads for the same reason.

Remember kids, just say no to Twelve-foot lanes on secondary roads.


  1. The average car lane is 15' on u.s. highways.

  2. Hello,

    Where did you find that? Everything I've read on the topic and a quick check on Google, including the DOT website, says 12'.15' seems much too wide...many cars are about that long.