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Publication Number: FHWA-HRT-09-057
Date: October 2009
Median U-Turn Intersection
FHWA Contact: Joe Bared,
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This document is a technical summary of the Federal Highway Administration report, Alternative Intersections/Interchanges: Information Report (AIIR) (FHWA-HRT-09-060).
Today's transportation professionals, with limited resources available to them, are challenged to meet the mobility needs of an increasing population. At many highway junctions, congestion continues to worsen, and drivers, pedestrians, and bicyclists experience increasing delays and heightened exposure to risk. Today's traffic volumes and travel demands often lead to safety problems that are too complex for conventional intersection designs to properly handle. Consequently, more engineers are considering various innovative treatments as they seek solutions to these complex problems.
The corresponding technical report, Alternative Intersections/Interchanges: Informational Report (AIIR) (FHWA-HRT-09-060), covers four intersection designs and two interchange designs that offer substantial advantages over conventional at-grade intersections and grade-separated diamond interchanges. The AIIR provides information on each alternative treatment covering salient geometric design features, operational and safety issues, access management, costs, construction sequencing, environmental benefits, and applicability. This TechBrief summarizes information on one of these alternative intersection designs—the median U-turn (MUT) intersection (see figure 1).
MUT intersections can be implemented as either full MUTs—where direct left turns from both the major and minor approaches are eliminated from the main intersection—or as partial MUTs—where direct left turns from only the major approaches are eliminated. On the major road, left turns are eliminated by requiring drivers to first travel straight through the at-grade main intersection and then execute their left turns by making U-turns at the median opening downstream of the intersection. They then must turn right when they reach the cross street. On the minor street, drivers who want to turn left onto the major road must turn right at the main intersection, execute a U-turn at a downstream median opening, and proceed straight through the main intersection. Figure 2 shows the geometric design of a full MUT, while figure 3 and figure 4 show the left-turn movements from major and minor roads for this design.
MUT intersections have been widely used in Michigan, particularly in the Detroit metropolitan area where many roadways were constructed with wide medians on wide right-of-ways. Partial implementations (keeping the cross street left turns at the main intersection) with similar concepts have appeared in Florida, New Mexico, and Louisiana. The MUT intersection typically is considered a part of a corridor treatment. The elimination of left-turning traffic from the main intersection as well as left-turn signal phases results in both operational and safety improvements for the MUT intersection design.
The primary design elements of the MUT intersection (see figure 2) are as follows:
Traffic Signal Control
The main intersection in an MUT intersection design is almost always signalized. A few unsignalized MUT intersections exist in Michigan, but these are limited to intersections with low volume cross streets. The crossover at an MUT intersection may or may not be signalized. Agencies should use standard signal warrants and/or guidelines for protected left turns in making the decision about whether to install signal control at the crossovers. The signals at the main intersection and the crossovers in an MUT intersection design have only two signal phases because direct left-turning traffic at the main intersection is redirected to a U-turn. Much of
the efficiency gained from installing MUT intersections stems from the two-phase signal operation.
The traffic simulation software VISSIM was used to compare the operational performance of the MUT intersection to a conventional intersection. Two geometric cases were simulated under six sets of traffic volumes. The reduction in signal phases at the MUT intersection provided increases in vehicle throughput ranging from 20 to 50 percent over the conventional intersection. While there is additional travel distance for those making left turns at an MUT intersection compared to a conventional intersection, the total network travel time savings at the MUT intersection usually
outweighs the travel time from the additional distance traveled.
An MUT intersection has 16 conflict points compared to 32 in a conventional intersection. Studies performed by the MDOT and the University of Michigan show that total crash reductions ranging from 20 to 50 percent can be expected with this level of conflict reduction.(3–5) Moreover, head-on and angle crashes that have high probabilities of injury are lower for MUT intersections compared to conventional intersections.
Candidate corridors for MUTs are medium to high speed four-lane divided highways. In rural areas, MUTs may be installed to address existing operational and safety needs and also anticipated needs when it is clear that the area may be developed into a more suburban setting. In existing suburban (and urban) settings, MUTs will result in immediate benefits in safety and operations, especially for through travelers on the major and minor streets.
MUT intersections are most readily applicable under the following conditions:
Highway agencies may decide that an MUT intersection is not applicable if left-turn efficiency is a problem or if right-of-way availability is limited.
A full MUT intersection reroutes both major street and minor street left-turning vehicles through one-way median openings located several hundred feet from the main intersection. This eliminates all left turns from the main intersection, reducing conflict points. It also allows two-phase signal controls at the intersection and the signalized U-turn crossovers. The benefits of the MUT intersection include increased capacity and safety. More details can be found in the full AIIR report available from the Federal Highway Administration.
Researchers—This study was performed by Principal Investigators Warren Hughes and Ram Jagannathan. For more information about this research, contact Joe Bared, FHWA Project Manager, HRDS-05 at (202) 493-3314, firstname.lastname@example.org.
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Key Words—Median U-turn, Alternative intersection, median U-turn intersection treatment (MUTIT), and MUT.
Notice—This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.
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Topics: research, safety, intersection safety, interchanges, non-signalized intersection, diverging diamond interchanges
Keywords: research, safety, diverging diamond interchange, DDI, alternative interchange, double crossover diamond, DCD