Why Don’t Small Traffic Circles on Neighborhood Streets Count as Roundabouts?

I remember when Northeast 39th and Glisan really was a roundabout (Dr. Know, WW, Sept. 14), before bureaucrats added stop signs. But what about the small traffic circles that make drivers swerve around them into the path of pedestrians? Wouldn’t speed bumps be safer and more effective? —Rich A.

As is often my wont, Rich, I’m going to use your question to answer a completely different question and hope that nobody notices. (Though who knows? If my supply of alkaloids holds out I might get around to answering your question as well.) So, why don’t the small traffic circles that litter our neighborhoods like so many blue-tarp dwellings count as roundabouts? I’m glad you asked!

At a nuts-and-bolts level, the difference between these little circles and true roundabouts is that streets approaching a roundabout have (a) yield signs and (b) medians separating the two lanes of traffic so you can’t enter the circle in the wrong direction. On a more philosophical level, however, traffic circles are intended as traffic calming devices, while roundabouts are also traffic control devices. It’s the difference between giving the traffic a Xanax and a warm blanket and giving it LSD and turning it over to a CIA hypnotist.

All right, perhaps that’s overly dramatic. Still, traffic circles mainly just slow traffic down and reduce side-impact collisions. Roundabouts do all that while also taking on the function of more traditional traffic control methods like signals or four-way stops.

Now, on to your speed bumps. (Lucky for you, I’ve got a few speed bumps left myself.) First, you’re almost certainly thinking of speed humps, the wide mounds you find in most Portland roadways that used to be good shortcuts. Speed bumps are what you find in parking lots where the speed limit is 5 mph; they’re maybe 1 foot wide and feel like you ran over a toddler.

Are speed humps better? Unlike circles, they can be deployed between intersections, and as you note, they don’t risk interfering with adjacent crosswalks. However, humps are also louder than circles, and they’re a bad choice for bus routes. (Buses can navigate traffic circles fairly easily as long as they’re not required to turn left at one.)

So, like anything else, it depends. What I really want to know is how the entire field of traffic engineering became solely about making it harder to get where you’re going. But I suppose that’s just the 20th century in me talking.

Questions? Send them to dr.know@wweek.com.