Posted this blog today talking about something I have a hard time
FORESTS, TREES, AND WHY ROUNDABOUTS INCREASE WALKER SAFETY
During a meeting with a Burlington (VT) city official this week, I was
asked to give a concise reasoning of how roundabouts increase safety
for walkers. In response quickly went into the studies, statistics,
etc., but forgot entirely the basic element which reduces the
frequency and severity of walker injuries: roundabouts by design
reduce the speeds of vehicles. Only by lowering speeds of vehicles
can one begin to address walker safety—and the only way to reduce
vehicle speeds is with concrete and steel impediments which
roundabouts and other traffic calming devices provide.
The roundabout reduces speeds by forcing an approaching vehicle to
divert from a straight line through placing a splitter island at the
approach point with a curb as the enforcer. After entry, the vehicle
continues to face constraint by having to travel on a circular curbed
travelway—the smaller the overall roundabout, the lower the
circulating speed. The entry and curved circular travelway
constraints on speed are called “deflection.” The one factor in all
walker safety research which most impacts on walker injury frequency
and injury severity is speed. The small mini-roundabout (like the
first one in Vermont built in Manchester Center last fall) features a
humped area in the place of a curbed central island—but a mini
generally can only be located at an intersection which has a fairly
low speed environment. And a mini only gets employed where a
roundabout with a curbed central island is not practical.
Of course other features of a roundabout aid in the overall walker
injury reduction—the splitter island providing a mid-crossing refuge
so the walker deals with traffic from one direction at a time, the
location of the crosswalk a car length from the actual intersection so
there are not left hand turning traffic issues, and crosswalk width
relatively narrow both reducing walker exposure and assisting in speed
reduction of vehicles.
So with roundabouts you do get up to a 90% reduction in injury rates
for walkers, and the U.S. and Canadian roundabouts record so far (no
fatalities to date) approximates that of France where they yearly
average about one walker fatality per 15,000 of their roundabouts
yearly (well over 30,000 there today).
Hope this gets the forest and trees back into proper perspective.
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