Dear Tom and Ray: I want your opinion about traffic- calming devices such as speed humps, chicanes, traffic circles and raised crosswalks.
As an urban planner, I’ve managed a traffic-calming program. Any talk of traffic calming, traffic management or both unleashed the most visceral reactions. For instance, citizens either cry out for local government to install speed humps to stop speeding, cut-
through traffic, or sue the government because they think the devices damage their vehicles.
Speed humps are designed to slow down a vehicle to the posted neighborhood speed limit, usually 20-25 mph. Do you think speed humps (not bumps) can cause undue damage to a vehicle?
– Kristina
Tom: We both very much favor “traffic calming.”
Ray: For the past 100 years or so, roads have been built to be efficient. The most efficient road is a smooth road in a straight line. That lets traffic travel as quickly as possible.
Tom: But there are places where you don’t want traffic to go as fast as possible. Like neighborhood streets where kids are playing or pets cross. So traffic calming intentionally makes some roadways less efficient by making them less straight and smooth.
Ray: Calming is not used on main thoroughfares, where efficiency is the priority.
Tom: There are a number of tools in a traffic calmer’s toolbox. There are chicanes, which put little “S-curves” midblock by using trees or sidewalk bump-outs as baffles.
There are sidewalk extensions that make the street narrower by expanding pedestrian space. And there are raised crosswalks and speed humps.
Ray: Unlike a speed bump, which is small and semicircular, a hump is a larger raised area. For instance, an entire crosswalk, or even an entire intersection, may be raised a few inches so that a car drives up a ramp, continues across, then comes down the other side.
Tom: As long as you approach it at a reasonable speed – say, 20-25 mph, in most cases – no harm is done to the vehicle. Hitting a pothole is far worse for a car than driving over a speed hump.
Ray: There has to be clear signage before a speed hump. It’s not fair to drivers to surprise them. Or even to post the speed limit somewhere else on the street, and let them pay the price if they exceed it.
Tom: It’s a safety issue. If a driver hits a speed hump without slowing down, the tires can leave the ground momentarily, making it impossible to stop or steer. And that’s very dangerous, especially because many humps are at intersections or crosswalks.
Ray: If you’re interested in traffic calming for your streets, go to trafficcalming.org. Then enlist neighbors and approach local officials. Now, if only someone would come up with “Brother Calming.”
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