NEW REPORT: Signals vs rotaries

December 17, 1996

NEW REPORT: Signals vs rotaries

Originally published in issue 10 of Tollroads Newsletter, which came out in Dec 1996.


Subjects:roundabouts signals

Agencies:Florida DOT

Richard Retting of the Insurance Institute for Highway Safety notes in a recent article ("Transportation Quarterly" 50/3 p27) that use of roundabouts in place of Stop signs or signals is "highly effective" in reducing crashes. Unfortunately ordinary Americans often think that traffic signals are the answer to intersection accidents and so there's constant clamor in cities and neighborhoods for more of the lights, and traffic engineers often try and protect city budgets from these pressures with various signal 'warrants.' Retting however notes that 37% of fatal accidents at intersections occur where there are signals and intersection crashes are the most common accident in cities, and the most deadly.

High-tech automatic cameras show some promise in deterring red-light running but they have a mixed record. And other accidents happen with signals. The truly dramatic reductions in serious accidents come from the use of the low-tech 'rotary' which through its concrete kerbs forces drivers to slow to a safe speed and reduces conflict points to merge and diverge movements, eliminating completely the potential for head-ons and right-angle crashes. The regular slowing of all entering vehicles reduces rear-enders too, as compared to the complete halts required at signals.

Florida DoT has just produced the "Florida Roundabout Guide" that makes these points and also documents the generally superior throughput of the continuous flow devices compared to signals. Roundabouts make better neighbors too than signals, since they don't back-up traffic, blocking driveways and requiring prohibitions on kerbside parking nearby. Maryland DoT which now examines roundabouts at all intersections proposed for signals is producing its own roundabout guide, and the FHWA is moving to do its own research on the rotaries. Other states where roundabouts are getting a hearing are Vermont, Michigan, and Colorado. They are the major form of intersection control off expressway interchanges in Europe. In the U.S. I-70 in the Vail Colorado area and the new MD-100 expressway in Howard County are each getting several roundabout interchanges, following excellent experience with earlier ones. (Contact Lap Hoang, Traffic Operations Office, FDoT 904 488 4284)

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