November 4


Roundabout Rule of Thumb for Preliminary Layout

By Mike Spack

November 4, 2011

Roundabout Design Rule of Thumb

Roundabouts are becoming increasingly popular.  Given their operating characteristics, I think they're better than traffic signals for controlling traffic at the main entrance into most developments.  Signals work best at intersections that have high traffic volumes over 8+ hours a day.  A lot of entrances into major developments (whether they're residential, commerical, or office) have big peaks in traffic for a few hours of the day, but often don't have sustained traffic throughout the day.  At off peak times roundabouts cause a lot less delay than signals.

A lot of the civil designers and landscape architects who put together the site layouts for major developments don't have experience with roundabouts.  Below is a sketch that can help site designers put together a rough layout for the entrance intersection (info is based on a class I took taught by Ourston Roundabout Engineering).  There's a lot of tweaking that will happen in the final design of the roundabout, but just knowing the rough diameter of the circle is enough to move ahead with the internal design of the site.


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Mike Spack

My mission is to help traffic engineers, transportation planners, and other transportation professionals improve our world.

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