October 1

# Using dashed striping to control speeds?

By Mike Spack

October 1, 2009

We recently finished reading Traffic by Tom Vanderbilt in my apprentice program.  It is my second time through the book and I think it is a must read for anyone dealing with traffic.  Tom does a good job of translating research so we can all understand it.  He deals mostly with the psychological aspects of driving, which us traffic engineers don't really study in college.

One of the book's takeaways for us traffic engineers is that people drive as fast as the environment tells them to.  I've personally seen this in my neighborhood.  I live in an eighty year old neighborhood on a grid system.  We have mature trees building a canopy over the road and we have sidewalks.  We also have a fair amount of cars parked on the street.  The natural speeds in my neighborhood are about 5 mph less than the speeds in Maple Grove where I was the city traffic engineer for a few years.  Amazingly, the residential streets in Maple Grove are slightly narrower than in my St. Louis Park neighborhood.  But they don't have sidewalks, trees, parked cars, etc.

So here is a crazy idea on how traffic engineers can subtly affect the roadway environment (I haven't found research on this specific idea, but I'd love to read about it if you have seen any test cases) – we should alter the skips on the pavement based on the speed limit.  The standard (no matter what the speed limit is) is for a 10 foot long white or yellow line, a 40 foot blank space, and then another 10 foot line.  Let's leave that on the 65 mph roads, but lets make the line shorter and have shorter gaps as the speed limit is reduced.  A human factors lab should do simulations to determine the correct length/gap ratios so we always "feel" like it is the same when we are going the speed limit – whether the speed limit is 30, 40, 55, or 70 mph.  The skip could be a subtle indicator to help our brains figure out the appropriate speed for the road.  If you are going too fast on a road with this new speed limit based configuration, it would start to seem like you are doing a Star Wars hyperdrive in the Millennium Falcon because the skips would be gong by "too fast."

• Brian says:

I think your idea could be a start b/c I definitely agree that environment can dictate the way we drive. Also seems like it would be inexpensive.
I’m not an engineer nor do I have any job that deals with traffic but I have a passion for driving and I commute over an hour a day and found Tom Vanderbilt’s book fascinating. His blog is how I found your site. Keep up the good work!