WHY ONLY ROUNDABOUTS AT HIGH SPEED (40 MPH AND OVER) BUSY INTERSECTIONS

Note this is an excerpt from a longer monograph written earlier this month.

Major Intersections along high-speed roadways (40 mph and above)--Roundabouts Only

The...Keene [NH] roundabout now going forward by the NHDOT [New Hampshire Department of Transportation] brings out the key reason why—and real world example--roundabouts are the only choice for intersections along high speed roads (40 mph and above)--something, as you know, comes from among others the counsel of Barry Crown, perhaps the most experienced roundabout designer and software author on the planet.  He deserves major credit (though with a lot of help and years of volunteer efforts as you well know) for the $60 million Keene Bypass project being stopped and converted to four roundabouts---one already built handling 60,000 average daily traffic.  The other Keene roundabouts are: (1) the first, a single laner in front of the Monadnock Region Medical Center and (2) a $4 million all-city-financed two laner at Marlboro/Main/Winchester Streets which forms a gateway to Keene State College and along with Central Square defines the downtown core.  

                  High speed intersections and the roundabout

That fifth Keene roundabout on a 55 mph speed zone will be between the Keene Bypass Roundabout and the Keene Turn Roundabout 15 miles distant in Brattleboro, about three miles from downtown Keene at NH 9/Base Hill Road cross intersection.  That intersection along a straight section of NH 9 at the bottom of a long ascending grade to the west has long been a high accident section.  After the latest NHDOT 2010 effort involving a median treatment on NH 9 outward from the intersection and further tweaking of the signals still led to another fatal crash within two years.  The NHDOT in fact truly wants to address the safety there and now--finally it must be said—decided to employ the only known treatment for high speed cross intersections providing a modicum of safety: the roundabout. To deal with the high speed approach NHDOT also intends to utilize a curving of the eastbound approach roadway (the downgrade), a recognized treatment, to constrain approach speeds from the west leg.  While the roundabout does not promise to be a cure all for crashes at high-speed intersections, it surely will reduce the numbers of crashes, the severity of any resulting injuries and avoidance of the T-bone crash.  And at high-speed intersections benefit cost for car travel is highest.  As you know, the Maryland State Highway Administration (MSHA) pioneered along with Florida and Vermont the beginnings of roundabout development in the eastern United States.  And MSHA used roundabout technology to respond to mostly rural high-speed (40-50 mph on one or more approaches) intersections where no solutions had been found to crashes with serious and fatal injuries—roundabouts slashed injury crashes by 88% (see FHWA website:

http://safety.fhwa.dot.gov/intersection/resources/casestudies/fhwasa09018/  ).

The Base Hill Road/NH 9 project for the NHDOT does stand above in priority in comparison to other choices, such as the three intersections (perhaps four when you consider the nearby entrance to the new NH 9 to a major shopping complex) along the Keene Bypass--all those intersections except Main Street involve no bicycles or walkers.  As you know a fatality for benefit cost analysis is valued at a  $6.1 million cost and an injury $126,000  (FHWA, 1999 dollars).  (Note the excellent Cambridge Systematics paper prepared showing metro fatalities and injuries more than twice the cost of congestion--the study sponsor, AAA supports a “zero fatality rate” policy, one it calls for declaration through a White House safety conference.)

The foregoing, as did my original message, places the high-speed intersections first and foremost the standard treatment for high speed intersections.  Of course, this entire discussion does apply at all across the lake in New York State (or Florida, Virginia and two Canadian provinces, Alberta and British Columbia) where the roundabouts unless unfeasible remain by policy the preferred treatment.  The New York State Department of Transportation (NYSDOT) backs up their “roundabouts only” policy with a central office roundabout design unit responsible for review of any NYSDOT investment in intersections where something other than a roundabout is proposed.  The fatalities along the US 7 corridor in Addison and Chittenden County alone--even in the absence of bicycle and walker usage--suggest the roundabout treatment even with acquisition of right of way when needed.  Note the Brattleboro Keene Turn Roundabout at $4 million arguably has already paid for itself in reduced injuries per year since 1999 when it was built--about 120 injuries based on the previous five-year rate and not including the one fatality in the last five years of the signal configuration.  And, as you know, tens of thousands of gallons of gasoline are saved each year at this intersection through conversion to a roundabout (note the VAOT study of delay). 

So, what continues today along US 7 major high speed intersections with sigs or signals amounts to a form of "Russian highway roulette" whether at Ferry Road in Charlotte, Ferrisbugh State Highway, VT 103 in Clarendon and the intersections north of that point to U.S. 4 in Rutland (all fatality crash sites), and yes, Little Chicago Road in Ferrisburgh.  Unfortunately conscious decisions to build higher injury rate signals rather than roundabouts at US 7/VT 103, Taft Corners and US 2/Industrial Drive in Williston (now nearing construction and speed limits along those roadway approaches are 30-35 mph) provide us with a test of safety performance of intersections where roundabouts were predicted to perform at a higher level but were rejected for traffic signals.  Over the next few years the wisdom of those choices can be easily observed.  Is it not fair today to conclude what will happen because of the rejection of the roundabout choice will not be pretty?   Finally, the discussion to this point addresses primarily the car mode only, not walking and bicycling aspect  (although a bicyclist fatality did take place at the US 7/Ferry Road intersection).