Economics

Caution: Debate Over Speed Bumps Ahead

Slowing traffic on a neighborhood street has economic costs and benefits.

Slow it down.

Photographer: Ken Hively/Los Angeles Times via Getty Images

A recent report from the U.K. suggested that the country eliminate speed bumps from its roads to ease vehicle passage and limit carbon emissions. This has since given rise to heated debate. In the U.S., homeowners often push for more speed bumps in their neighborhoods to slow drivers, making local routes for deliveries more cumbersome each year. But -- from the point of view of an economist -- are these bumps actually a good idea? 1

On one hand, the bumps slow down traffic, and that probably saves some lives. Yet the calculus is not so simple, in part because speed bumps bring unintended secondary consequences. Many cars or trucks swerve around them, which is arguably more dangerous than having no obstacle in the first place, or drivers may rev up their engines to accelerate once the bump is past. The constant "bump bump" noises or screeching brakes have led many nearby homeowners to request that the bumps be removed. The bumps may drive too much traffic to alternate routes, and they slow down the response of emergency vehicles.

Traffic obstacles also raise the cost of deliveries sent to our homes, such as by UPS or FedEx truck. The result may be more individual trips to retail stores, which may boost the number of accidents and deaths. Don't assume that apparent safety precautions always means more safety, as economic inefficiencies bring their own dangers, even if they are less visible.

One way to systematically evaluate speed bumps would be to look at home values in streets with and without the bumps, as you might think that safer homes would sell for more. But one study (with imperfect controls) found no difference in real estate values, so that doesn't settle the question.

Another economic approach would consider whether the private sector, when trying to accommodate customer demand, finds that speed bumps help or hurt business. That's a kind of market test of the concept, and indeed I often see speed bumps in shopping mall parking lots, to slow down traffic and ease the risk of accidents, including to pedestrians. The mall and parking lot owners have decided that the benefits of greater safety will attract more customers than the inconveniences of driving more slowly, and other possible costs, will put customers off. That is a seat-of-the-pants cost-benefit test, and it suggests some role for the bumps in the broader world.

That said, my personal impression is that these private-sector speed bumps are smoother and gentler than the ones I often find in neighborhoods. When it comes to local roads, the residents are actively trying to keep outside drivers away, whereas the shopping mall and parking lot owners seek the best overall environment for commercial reasons. As a tentative conclusion, I think some speed bumps are a good idea, but many are too obstructive, and perhaps they are too numerous as well; this view is supported by some recent research.

Another angle of the speed bumps debate is how much it revolves around issues of symbolic value, and that in part explains why the discussion can become so heated.

By its very design, a speed bump is a deliberate obstruction with maximum transparency as such. It is sending a message that the social goals of safety or neighborhood quiet are sufficiently important that it is worth slowing people's progress when they travel. There are many regulations that try to make our lives safer, but most of them are hidden, with nontransparent costs, such as auto-safety regulations as applied through crash tests. A speed bump, in contrast, can work only if people notice it each time. So to the extent a society accepts speed bumps, it is visibly advertising the notion that limits to fast transportation -- a symbol of progress -- are acceptable in the name of safety and cozy locality.

You might be wondering why, in such a high-tech era, we need speed bumps at all. Why not use cameras or sensors to detect and deter speeders and other irresponsible drivers? There are at least two reasons: greater expense and privacy. Many people in a neighborhood don't want there to be an electronic record of their comings and goings, and thus they are willing to embrace what is essentially a Stone Age technology.

In sum, one side of the speed bumps debate feels it is up against enemies of smooth transport and progress, while the other is seeking to protect privacy and comfortable communities.

Since both progress and privacy are in such scarce supply these days, is it any wonder that everyone goes away unhappy?

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

  1. Some sources distinguish between speed "bumps" and speed "humps." Most of the analysis here applies to a variety of traffic barriers.

To contact the author of this story:
Tyler Cowen at tcowen2@bloomberg.net

To contact the editor responsible for this story:
Stacey Shick at sshick@bloomberg.net

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