Roundabouts

Roundabouts: Efficiency, rules of the road

Roundabouts save time and increase efficiency by keeping traffic moving.

This one is a "stretch" of variable length, depending on circumstances.

The first problem with this statement is that "moving" traffic means a nominal 15-18 mph, under optimum conditions. Thus, under the best driving conditions, the roundabout still makes you slow down (it's like an always-almost-red-signal). Three quarters of a vehicle's kinetic energy is given up in decelerating from 35 mph to 15-18 mph. It's not much worse if you come to a complete stop.

Second, when demand exceeds capacity, a roundabout will develop queues. It's a simple fact that if you try to put more cars through any intersection than it can handle, backups occur. Traffic signal, roundabout-- doesn't matter a hoot (or a honk?).

The third unstated problem is that a roundabout can be easily blocked by an accident, or even by a crossing pedestrian. A block on any of the exits can easily turn into a block for all directions of traffic. For example, if a crosswalk is located 1 car length downstream from an exit, a second car that wants to use that exit while a pedestrian is crossing will partially or entirely block thru-traffic on the roundabout.

Rules of the road are simple.

Not if you think about them.

A good example of complications is provided by a Golden, CO "Safety and Etiquette" brochure. These folks have (hopefully) thought a lot about this. Let me quote just two of their "Yield rules":

"You must yield to traffic already in the roundabout."
"All vehicles must yield to pedestrians in crosswalks."
"All vehicles must yield to buses and semi truck trailer combos."

Does this sound like an intersection meant to move traffic? What do I do when I am driving in the circle and a truck approaches? Personally, I'll yield to the truck, but what should a truck driver expect or do?

Rules-of-the-road have an additional complication: based on my observations of the Los Alamos San Ildefonso roundabout, I think that the rules of the road have "local variations" that lead to confusion for non-local drivers. These can be learned by local drivers, but can be a major source of confusion to drivers who are unfamiliar with the local customs.