Roundabouts: Generic pros, cons, and questions

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In this section, I'll weave together some of the frequently discussed pros, cons, and questions re. roundabouts. "Pro's" will be enclosed in green boxes, "Con's" in red boxes, Questions and unresolved issues in yellow boxes, and my additional comments and thoughts with plain or bulleted text. Initially this section was to be completely general, but references to the Los Alamos NM502 Corridor Study have crept in, and these are indicated using violet text enclosed in [].

A jargon of euphimisms and sales points for roundabouts has built up over the years, with many of the claims becoming akin to "doublespeak" (remember Orwell's 1984?). As purchasers and users of roads, it is up to us to distinguish between reason and hype-- both positive and negative.

Let's start out with some very general points that are often discussed.
If it works for them (UK, Golden, CO, etc.), it ought to work for us.
Comparisons too often involve apples vs. oranges.

The devil is in the details. Performance claims are seldom accompanied by even the minimum of factual information. The data I miss the most are the roundabout diameter, peak hourly traffic volume, and performance data during peak hours-- perhaps average delay time through the intersection or peak queue length.

The relevance of the examples chosen is often dubious. The most common misleading comparisons I've seen involve showing similar roundabouts where traffic is lower than the proposed application. Note that a driver's qualitative estimate of the traffic volume is not reliable enough to compare different applications, since the difference between moderate and severe congestion is only 15-25% in volume.

[The Sedona, AZ example used by MIG has peak traffic volume that is typically 25% less than that of Trinity. Worse, the famous Golden, CO roundabouts are two-lane roundabouts (except for one), while those being considered for Trinity are single lane.]

Examples of impressive successes are generally part of the proponents' pitch. Examples of disastrous failures are rarely, if ever, discussed. If you'd like to read about some marginal or failed roundabouts, take a look these places where roundabouts have been or will be removed: Bicycle Blvd. (Santa Rosa, CA), Lynch Roundabout (UK), and Highbury roundabout (UK). There has also been at least one roundabout trial of several months' duration where the roundabout approach was dropped: Claremont, CA.

Also, take a look at the first 40 seconds of this pro-roundabout video in Glens Falls, NY; this one is a real mixed bag (just like a roundabout), but it's too much fun to miss. Everyone who talks in the video loves their roundabout. But, while the business men are standing in front of the roundabout, saying how great it is, in the background you hear loud traffic, tire squeals, and see the second pedestrian trotting across the 2nd leg of the crosswalk.  [One other thing worth noting about the Glens Falls installation is that the intersection where it is installed is a business district hub, more analogous to Central Ave. in Los Alamos than to Trinity Drive or East Road.]

Now consider two claims that I find interesting when juxtaposed:
Roundabouts have a calming effect on traffic.
Roundabouts raise drivers' anxiety, which is helpful.
With friends like this...?

Hmmm. Traffic is calmed while drivers are intimidated? Gaining one at the cost of the other hardly appeals to me. I would define the term "traffic calming" as putting obstacles in the way of cars so it's harder to get where you want to go. Both a friend of mine and myself have a similar assessment of roundabouts, based on roundabout driving experience in different parts of the country: "...some moments of sheer terror." A different friend and myself think of roundabouts as a concrete and steel version of the game of "chicken". I'm not especially in need of such stimulation. Are you?

BTW, take a look at this video from Clovis, NM-- it looks like this driver's anxiety was not high enough. To be fair, if the driver was sleeping or drunk or had a heart attack, perhaps the roundabout was beneficial compared with a traffic signal.

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