Dear Tom and Ray: I'd like to gauge your opinion about the installation of traffic-calming devices such as speed humps, chicanes, traffic circles, raised crosswalks, etc. Speed humps, as you probably know, are the most ubiquitous traffic-calming devices. As an urban planner, I've had the opportunity to manage a traffic-calming program for a local municipality. While carrying out the goals of this program, I noticed that any discussion of traffic calming and/or traffic management unleashed the most visceral feelings and reactions in the general public. Citizens either cry out for their local government to install speed humps to stop the speeding, cut-through traffic from traveling through their neighborhoods, or they sue the local government because they believe that the devices cause damage to their vehicles. What are your thoughts? Speed humps are engineered and designed to slow a vehicle down to the posted neighborhood speed limit, usually 20-25 mph. Do you think that speed humps (not bumps) can cause undue damage to a vehicle?

Kristina

Tom: To answer your general question, we are both very much in favor of this thing called "traffic calming."

Ray: Unlike a speed BUMP, which is literally just a small, semicircular bump, a speed 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 onto this platform, continues across it and then comes down on the other side.

Tom: As long as you approach it at a reasonable speed -- say, 20 to 25 mph, in most cases -- absolutely no harm is done to the vehicle. To put it in perspective, hitting a pothole is far worse for a car than driving over a speed hump is.

Ray: Our only caveat is that there has to be clear signage in advance of a speed hump. It's not fair to drivers to simply 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 actually a safety issue. If a driver hits a speed hump without slowing down first, the tires can leave the ground momentarily, making it impossible to stop or steer. And that's very dangerous, especially because many speed humps are located at intersections or crosswalks.

Ray: So with adequate signage, we wholeheartedly endorse traffic calming as a way to discourage idiots from speeding through residential areas. If you're interested in traffic calming for your neighborhood, use this Web site as a resource: www.trafficcalming.org. Then get together with some neighbors, and bring this idea to the attention of your local officials. Now, if only someone would come up with "Brother Calming."

But we should explain what it is.

Ray: For the past 100 years or so, roads have been built to be efficient. And the most efficient road is a smooth road that goes in a straight line. That allows traffic to travel as quickly as possible.

Tom: But there are some places where you don't want traffic to go as fast as possible. Like on neighborhood streets where kids are playing, or where pets cross the street, or where older folks are enjoying their front porches and gardens. So traffic calming intentionally makes some roadways less efficient by making them less straight and less smooth. And these changes force drivers to slow down.

Ray: Traffic calming is not used on main thoroughfares, where efficiency IS the top priority. But on neighborhood streets, where commuters from outside the neighborhood speed through, traffic calming can provide great benefits.

Tom: There are a number of different "tools" in a traffic calmer's toolbox. There are chicanes, which put little "S-curves" in the middle of a block 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.