Can’t We All Just Calm Down?

Q: There is a lively discussion online about the new choker curbs on a road in Richland, half the people supporting them and half saying the city has created an unsafe condition. I would appreciate any thoughts you have on the effectiveness of traffic calming devices, how they work, the legal basis for them, and how local drivers adapt to the changes.

A: When someone is really fired up, have you ever tried telling them to just calm down? How’d that play out? And when someone is driving too fast, does telling them to slow down work? Maybe for some, but we have more options.

Traffic calming has two primary goals: slower speeds and less traffic. Although related, we’ll leave traffic volume for another day. We can sort two common speed-reduction approaches into big buckets I’ll call physical and behavioral.

Physical strategies involve making changes to the roadway that compel drivers to respond. Traffic engineers break this into three methods: horizontal deflection (preventing drivers from traveling in a straight line, using tools like lane shifts, chicanes, and roundabouts), vertical deflection (like speed humps that force drivers to slow down to avoid discomfort), and street width reduction (which includes corner extensions, median islands, and chokers).

Behavioral strategies are essentially messages telling you to slow down. We get these messages in a variety of ways, some more palatable to drivers than others. At the low-impact end are things like traffic safety PSAs and roadside crosses. At the other end we have officers making traffic stops and automated speed cameras.

What works? TV ads and roadside memorials on their own result in limited behavior change. Writing tickets works better, but it’s not perfect. I’ll interject a personal story here. Back when I was a deputy, I contacted a driver for speeding and he promptly held up a copy of a speeding ticket he’d just received. He barely made it 25 miles. Automated speed cameras might be the most effective of the behavioral strategies. Outcomes in Seattle and Kirkland have shown that about 90 percent of drivers who get one speed camera ticket don’t get a second one.

Physical strategies have a more universal impact. When the driving environment changes, it affects all drivers. Choker curbs bump out mid-block to narrow the roadway, which reduces the margin of error for drivers, resulting in slower speeds. They’re appropriate for almost any speed limit and traffic volume. This often makes them a better choice than speed humps, which are for slower, lower-volume roads.

Traffic calming measures are a common tool in road design, and traffic engineers have lots of guidance on how and when to use them. According to the Federal Highway Administration, few jurisdictions have been sued for traffic calming measures, and the limited successful lawsuits were because the measure was implemented incorrectly, not because it was inherently unsafe.

I took a look at the online conversations about your choker curbs, and from the images folks posted it’s clear that some drivers are learning about them the moment their bumper hits the warning sign. It’s preferable for drivers to learn new behaviors without damage to vehicles and signs, but maybe those pictures are evidence that there are patterns of dangerous driving on this road (like speed and inattention) that need to be addressed.

There isn’t one perfect tool that will solve dangerous driving. Combining physical interventions like choker curbs with behavioral interventions like traffic enforcement is better than one or the other. And when we add other tools, like vehicle technology, land use, and smarter speed limits, roads become safer for everyone.