Roundabouts: Efficiency, rules of the road

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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.

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