To The Daily Sun,
In roundabouts, vehicles travel counterclockwise around a raised center island, with entering traffic yielding the right-of-way to circulating traffic. In urban settings, entering vehicles negotiate a curve sharp enough to slow speeds. The McFarland Johnson presenter at the Meredith Selectboard workshop specified that speed to be 15-18 mph in the Meredith application. Within the roundabout and as vehicles exit, slow speeds are maintained by the deflection of traffic around the center island and the relatively tight radius of the roundabout and exit lanes.
Modern roundabouts are much smaller than older traffic circles or rotaries and require vehicles to negotiate a sharper curve to enter than their older counterparts did. These two differences are what make travel speeds in roundabouts slower than speeds in traffic circles. The lower speeds mean reduced severity of accidents when they occur.
Roundabouts promote safety in several ways. The most common types of intersection crashes are right-angle, left-turn, and head-on collisions. The severity of collisions increases with vehicle speed. These types of crashes are mitigated in roundabouts because vehicles travel in the same direction at speeds less than 20 mph. Replacement of traffic signals with roundabouts can reduce the likelihood of rear-end crashes and their severity by removing the incentive for drivers to speed up as they approach traffic signals and by reducing abrupt stops at red lights. Do we have issues with the number of crashes in downtown or their severity?
Relative to other age groups, senior drivers are over-involved in intersection crashes. Older drivers' intersection crashes often are due to their failure to yield the right-of-way. Traffic flow at roundabouts is both slower and uni-directional, making the consequence for failing to yield is less severe. Particular problems for older drivers at traditional intersections include left turns and entering busy thoroughfares from cross streets. Roundabouts eliminate these situations entirely.
With that said, roundabouts themselves can be confusing. Extra signage and street marking is recommended as part of their use. When multiple roundabouts are placed in close proximity it amplifies driver uncertainty. Uncertainty is not an aid to traffic safety. Making combination two lane- one lane-roundabouts has very limited data available for review. Placing a combination two lane- one lane-roundabout sandwiched between two smaller single-lane roundabouts is likewise a lightly studied application.
To the extent that you agree with lowering the speed limit on Interstate 93 down to 55 mph you probably agree that roundabouts are a safety aid. With that said there is very limited information available on the effect of placing multiple roundabouts in a relatively concentrated area as is being proposed in Meredith. There is a reason why McFarland Johnson and NHDOT do not want to own the recommendation for placing three roundabouts in downtown Meredith. Sometimes balance between safety and other considerations is struck ... that's one reason the speed limit on Interstate 93 is 70 not 55.
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