Size of roundabout needed for FM1626

As I have written many times, I have nothing against roundabouts, per se. In fact, I think they are kind of cool in the right place. My problem is, I am still not convinced a road with a 55-60 mile-an-hour posted speed limit is the right place.

I know roundabout champion and Kyle Assistant City Manager James Earp has produced all kinds of charts and graphs proving how safe roundabouts are, but none of his charts and graphs indicate if or when a study has been conducted on a roundabout placed on a four-lane divided highway such as FM 1626 where the speed limit is between 55 and 60 mph (and actual driving speeds are closer to 65). His charts show quite conclusively that roundabouts require motorists to reduce their speeds to negotiate the curvature, but he has produced nothing to show how many feet is required to slow the speed to the safe limit when the motorist is driving as fast as they do on FM 1626.

My limited research provided me with only one roundabout that has ever been constructed on a highway with a speed limit of 60 miles an hour and that highway is the 23-mile-long A612 which originates in England’s central Nottingham and ends in Averham. However, the speed limit on that part of the A612 where the roundabout is located is only 40 miles an hour and, at that point, the A612 is a two-lane road.

Then I ran across this interesting document prepared by the U.S. Department of Transportation, no less, which indicates that a roundabout on a road like FM 1626 would be required to have a radius (not a diameter, but a radius) of 250 feet. That seems to me to be a fairly large structure However, if the speed limit on 1626 between Kohlers and Marketplace was reduced to, say, 45 miles an hour, the required radius would be only around 150 feet, a significant size reduction.

This study also mentioned something else about roundabouts on four-lane roads such as 1626. As Mayor Pro Tem Damon Fogley correctly pointed out, they would reduce the number of collisions in which one vehicles smashes into another at a 90-degree angle. "However," the Department of Transportation study says, "at multilane roundabouts, increasing vehicle path curvature creates greater side friction between adjacent traffic streams and can result in more vehicles cutting across lanes and higher potential for sideswipe crashes."

So instead of the type of car crashes you’re likely to see while watching a Grade B cops-and-robbers movie, you’re more likely to see FM 1626 becoming a miniature NASCAR track with those types of accidents.

Pick your poison.