Sunday, March 8, 2015

Crossing an Intersection on Foot—Improved Safety Equals Constraining Vehicle Speeds

Crossing an Intersection on Foot—Improved Safety Equals Constraining Vehicle Speeds 

When it comes to improving safety at busy urban intersections, improving safe movement for those on foot requires some physical constraint on vehicle speeds.

There exists a common belief that placing signals at an intersection improves pedestrian safety.   That may or may not be the case.  But generally signals offer little difference in pedestrian injury rates compared to sign control.  Swedish highway authorities use the same formula to measure walker safety whether the intersection has stop signs or a traffic signal.

The one overwhelming truth about intersections is that frequency and severity of pedestrian injuries depend on prevailing vehicle speeds.  And the best way to constrain speeds of vehicles comes in the form of traffic calming—speed humps/bumps, median diverters which provide a center street refuge as well as forcing a slight divergence of the straight line vehicle travel which reduces vehicles speeds, and the roundabout.

Consider the “race through the stale green” by a vehicle approaching a signal, violating right turn on red, and a vehicle blowing through a red signal—and the connection between speed and walker crash vulnerability at signals becomes clear.  

The roundabout does a lot of things to improve walker safety—such as, providing a median refuge, moving those crossing from several vehicle conflicts, etc.—but most importantly the roundabout slows vehicles.  There now exists plenty of research and U.S. experience to confirm the traffic calming effect of the roundabout and improved walk mode safety.  The fact there are about 4,000 roundabouts in the U.S. and Canada built since the first in 1990 without a pedestrian fatality should be enough to convince anyone of the safety provided to those who walk.  Urban Melbourne with 4,000 roundabouts recorded zero fatalities in one five year period—Burlington recorded two fatalities at 75 signalized intersections in just 15 years!  (This does not include the fatality just across the border in So Burlington at the Sheraton/Stables crosswalk last September.)  France with its 33,000-plus roundabouts offers a similar indication of walk mode safety—one pedestrian fatality per 15,000 roundabouts per year.  The traffic calming effect of a roundabout extends outward one to two blocks distant.

For all of us the first criterion to be considered when investments are proposed at intersections supposed to benefit walk mode safety must be:  does that investment reduce vehicles speeds?  Any answer of “no” to that question must give one pause as to why that investment is necessary—and, more importantly why not also include in that project traffic calming which forces vehicle speed downward?  Both Alberta and British Columbia ministries of transport adopted a simple rule for intersections a few years ago—if something more than two-way stop control is required the roundabout is the first choice.

Slowing vehicle speeds does not mean greater travel time for the car.  A study of over 50 roundabout corridors in the U.S. found little change—some slightly longer times, some slightly slower times—for through travel.  Reduced wait times at signals compensated for the lower prevailing speeds along the roundabout corridor compared to a signalized corridor.

So, when examining intersection investments to improve walker safety the first criterion to be addressed is: are cars speeds reduced through physical constraint?