A Michigan left is an at-grade intersection design which replaces each left turn with a U-turn and a right turn. The design was given the name due to its frequent use along roads and highways in the U.S. state of Michigan since the late 1960s. In other contexts, the intersection is called a median U-turn crossover or median U-turn. The design is also sometimes referred to as a boulevard turnaround, a Michigan loon or a "ThrU Turn" intersection.
The design occurs at intersections where at least one road is a divided highway or boulevard, and left turns onto—and usually from—the divided highway are prohibited. In almost every case, the divided highway is multi-laned in both directions. When on the secondary road, drivers are directed to turn right. Within 1⁄4 mile (400 m), they queue into a designated U-turn (or cross-over) lane in the median.
When traffic clears they complete the U-turn and go back through the intersection. Additionally, the U-turn lane is designed for one-way traffic. Similarly, traffic on the divided highway cannot turn left at an intersection with a cross street. Instead, drivers are instructed to "overshoot" the intersection, go through the U-turn lane, come back to the intersection from the opposite direction, and turn right.
When vehicles enter the cross-over area, unless markings on the ground indicate two turning lanes in the cross-over, drivers form one lane. A cross-over with two lanes is designed at high-volume cross-overs, or when the right lane turns onto an intersecting street. In this case, the right lane is reserved for vehicles completing the design. Most cross overs must be made large enough for semi-trailer trucks to complete the cross over. This large cross-over area often leads to two vehicles incorrectly lining up at a single cross-over.
When the median of a road is too narrow to allow for a standard Michigan left maneuver, a variation can be used which widens the pavement in the opposite direction of travel. This widened pavement is known as a "bulb out" or a "loon" (from the pavement's aerial resemblance to the aquatic bird). Such a design is sometimes referred to as a Michigan loon; in Utah, as a ThrU Turn, which is a portmanteau combining the terms "Through" (the intersection, followed by a) "U Turn".
The Michigan Department of Transportation first used the design at the intersection of 8 Mile Road (M-102) and Livernois Avenue ( ) in Detroit in the early 1960s. The increase in traffic flow and reduction in accidents was so dramatic that over 700 similar intersections have been deployed throughout the state since then.
The design is relatively common in New Orleans, Louisiana, and its suburb Metairie, where city boulevards may be split by streetcar tracks, and suburban thoroughfares are often split by drainage canals. Some intersections using this design are signed similarly to those in Michigan, but with more descriptive text, however in some cases the only signage is "No Left Turn" and local drivers are left to figure it out for themselves.
The city of Plano was the first city in Texas to use a Michigan left. One was built in mid-2010 at the intersection of Preston Road and Legacy Drive. In January 2014, the city announced plans to revert the turn to a traditional intersection as a result of drivers' confusion.
The city of Draper, Utah, a suburb of Salt Lake City, announced in 2011 that it would be building Utah's first "ThrU Turn" at the intersection of 12300 South and State Street, just off Interstate 15 through Salt Lake County. Construction began in summer 2011 and was completed in fall 2011.
Also in the Salt Lake City area, the suburb of South Jordan implemented a temporary "ThrU Turn" at the intersection of 7800 South and Bangerter Highway. The intersection was in use during construction of a Single-point urban interchange at that location but has since been removed as construction is complete.
A set of four Thru Turns is scheduled to be implemented in Layton, Utah, to help alleviate congestion caused by four intersections within close proximity. Construction should begin in summer 2014.
Since the redevelopment of the interchange between University Boulevard (MD 193) and Colesville Road (US 29) in Silver Spring, Maryland, a Michigan left has been used to increase efficiency of traffic through an otherwise underdeveloped and congested intersection. Due to its proximity to the Capital Beltway, heavy traffic is handled more safely and efficiently.
In 2009 the Victorian state government in Australia announced the introduction of a "P-turn", similar to the Michigan left, in the southern Melbourne suburb of Frankston. Traffic in Australia drives on the left: the P-turn requires right-turning vehicles to turn left then make a U-turn.
In Mexico, Guadalajara has a grade-separated variation of this setup in the intersection of Mariano Otero Avenue and Manuel Gómez Morín Beltway ( ). Traffic flowing through Mariano Otero is routed through an overpass above the beltway, with two access roads allowing right turn on all four possible directions; the U-turns, meanwhile, are built underneath the beltway and allow the left turn from Mariano Otero avenue to the beltway. U-turn intersections are very common throughout Mexico, particularly in Mexico City.
Brazil is also known to utilize this setup especially in São Paulo.
Applicable traffic studies
This type of intersection configuration, as with any engineered solution to a traffic problem, carries with it certain advantages and disadvantages and has been subject to several studies.
Studies have shown a major reduction in left-turn collisions and a minor reduction in merging and diverging collisions, due to the shifting of left turns outside the main intersection. In addition it reduces the number of different traffic light phases, significantly increasing traffic flow. Since separate phases are no longer needed for left turns, this increases green time for through traffic. The effect on turning traffic is mixed. Consequently, the timing of traffic signals along a highway featuring the design is made easier by the elimination of left-turn phases both on that highway and along intersecting roadways contributing to the reduction of travel times and the increased capacity of those roadways.
It has been shown to enhance safety to pedestrians crossing either street at an intersection featuring the design, since they only encounter through traffic and vehicles making right turns. The left-turning movement, having been eliminated, removes one source of potential vehicle-pedestrian conflict. One minor disadvantage of the Michigan left is the extra distance required for the motorist to drive. Sometimes the distance to the turnaround is as far away as 1⁄4 mile (400 m) past the intersection. This design leads to each motorist driving an additional 1⁄2 mile (800 m) to make a left turn.
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|Wikimedia Commons has media related to Michigan left.|
- Michigan Left at Michigan Highways
- Synthesis of the Median U-Turn Intersection Treatment, Safety, and Operational Benefits
- Animation of a Michigan Left
- FHWA: MUT Case Study – Michigan Avenue at South Harrison Road in East Lansing (Michigan), published July 31, 2014