I received an e-mail from a reader who wondered why roundabouts weren't included in my last column.
The term roundabout has a very nice sound to it; not like the nasty sounding thing called a traffic circle. Traffic circles are for places like New Jersey and Washington, D.C. Traffic circles make drivers say bad words. Roundabouts are fun and you go around them with a smile on your face. Roundabouts are for Maryland.
In Massachusetts they often are referred to as rotaries. The fact is, call it what you wish, it is a circle with vehicles going around counterclockwise, at least here in America.
At this point I can hear someone saying, ''Oh, no Dave, you've got it wrong. Circles make the circle traffic yield to entering traffic and roundabouts make the entering traffic yield to traffic already in the roundabout.''
It isn't that simple.
The traffic circle or roundabout has its origins in the days of animal-powered vehicles. Things were considerably slower then and two horses jostling with each other was not considered a traffic accident, although two drivers beating each other with horse whips was considered downright unfriendly.
Many grand traffic circles were constructed with monuments in the middle. Some weren't even round. Philadelphia has four squares in the downtown area that operate like traffic circles; they have parks in the middle.
With the advent of the automobile, speed was now five times greater and the big flaw with traffic circles became painfully clear; they lock up. Lockup means that no vehicle can either enter or exit the circle until police arrive and force drivers to go in directions they don't want to go to unlock things.
The problem occurs when traffic volume exceeds the traffic-carrying capacity of the circle. It is most pronounced when circle traffic must yield to entering traffic.
Spectacular lockups occurred along many East Coast highways, most notably on New Jersey arterial roads because they made high-speed, high-volume main road traffic the priority movement at traffic circles. This worked until two high-speed, high-volume main roads intersected at a traffic circle; wham, lockup and virtual horse whip fights.
Somewhere in the 1960s the Brits, who had many traffic circles of their own, had the idea of slowing things down by making all entering traffic yield to the traffic in the circle. This made a lot of sense, especially anywhere within 100 miles of London, since traffic had long since ceased to move at anything faster than a furlong-per-fortnight.
That little adventure in British traffic engineering was the beginning of the roundabout movement. The truth is, under certain circumstances, the roundabout is the preferred way to handle traffic at two or three intersecting roads.
Roundabouts come in a variety of sizes, but in the main they are much smaller than traffic circles because they do not have to account for queued vehicles within the geometric confines of the circle waiting for a break in traffic to exit the circle.
Oh, yes, the circumstances where a roundabout should be considered: stable and predictable traffic volumes, slower speeds and nice, friendly drivers. There are a variety of other technical and political reasons, but those three are the most important, at least to this traffic engineer.
Properly designed (this is really important), roundabouts are safer, more efficient, environmentally friendly and cheaper than traffic signals. They won't work in most highvolume arterial situations, but roundabouts have become a valuable tool in the traffic engineer's box of tricks.
A parting note: A number of years ago on a business trip to England, I, and another traffic engineer, rented a car in the suburbs of London. With absolute trepidation we embarked upon the adventure of driving on the left side of the road. We were feeling pretty good about our efforts until we approached a roundabout. We simultaneously uttered the same expletive and pulled off the road. Upon planning our maneuvers carefully and noting where we wished to exit according to the map and posted signs, we entered. Wow! Have you ever done the Macarena while driving a car?
By Dave Humphreys
Source: The Capital