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In fact, for the RCUT design, the median U-turn offset is perhaps the most important design parameter affecting the operation and safety of the intersection at rural high-speed locations.
To develop crash prediction models, the researchers compiled data on the geometric layouts, average annual daily traffic (AADT), speed limits, and crash records related to 35 RCUT intersections--12 in Maryland, 5 in Minnesota, 5 in Missouri, and 13 in North Carolina.
Next, the researchers used the crash rates and the median U-turn offsets computed for and measured from each RCUT site to develop the crash prediction statistical models.
The researchers developed separate crash prediction models for two types of RCUT designs: RCUTs without right-turn acceleration lanes (based on data from Minnesota and North Carolina) and RCUTs with right-turn acceleration lanes (based on data from Maryland and Missouri).
"The 35 rural RCUTs sampled from four States cover a wide enough range of traffic demands to provide insights into the typical range of conditions under which engineers might consider installing an RCUT to achieve the desired level of safety," says Monique Evans, director of FHWA's Office of Safety Research and Development (R&D).
For an RCUT with a right-turn acceleration lane, assuming it is separated from the major road by grass or concrete, after the driver has traveled about 1,020 feet (311 meters) of the acceleration lane in order to join traffic on the major road, a U-turn offset of 1,500 feet (457 meters) will leave only 480 feet (146 meters) within which the driver can find a gap to change lanes and then decelerate to 15 miles (24 kilometers) per hour at the U-turn opening, which is insufficient in most cases.
The observational data and the crash analyses indicate that the RCUT design offers a substantial safety benefit, while the travel time penalty is small.
At rural expressways, longer travel distances to the U-turns for through and left-turning traffic from the minor road will require longer overall travel times for the RCUT than at conventional intersections.
Extensively used at locations in Maryland and North Carolina, the RCUT has a proven track record of safety benefits, attributable to reduced vehicle-to-vehicle conflict points.
FHWA also has analyzed the safety of RCUT intersections, specifically a selection of those built in Maryland, versus a control group of intersections.
169 in Belle Plaine, MN (2002-2011) Timeframe Right-Angle Crashes/Year At Grade Full Access 2002-2005 15 Signalized Intersection 2005-2007 11 RCUT 2009-2011 0 Source: MnDOT.
So, in 2009, MnDOT installed an RCUT, which has nearly eliminated crashes.
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