A Michigan left, sometimes known as a Michigan Turn, median U-turn,[1] median U-turn crossover,[2] or Boulevard Turnaround,[3] is an automobile traffic maneuver in which a combination of a U-turn and a right turn or a right turn and a unidirectional U-turn replace a prohibited left turn. The term was coined because the arrangement is quite common along Michigan roads and highways. The Michigan left has been a part of Michigan roadways since at least the late 1960s,[4] and a MDOT animation is available here. Michigan lefts are also common in the New Orleans, Louisiana, area.
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Description
Michigan lefts occur at intersections where at least one road is a divided highway or boulevard. Left turns onto—and sometimes 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 a 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. For additional safety purposes, the U-turn lane is designed so traffic only flows through it one-way.
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 lineup, unless markings on the ground indicate two turning lanes in the cross-over, drivers are to line up single file. A cross-over with two lanes is usually designated at high volume cross-overs, or when the right most lane is proceeding forward to an intersecting street. In this case, the right most lane is reserved for vehicles completing the Michigan Left. 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.
Locations
The Michigan left was initially piloted by MDOT at the intersection of 8 Mile Road (M-102) and Livernois Avenue(map) 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.
In 2009 the Victorian state government in Australia announced the introduction of a "P-turn", similar to a Michigan left, to an intersection in the southern Melbourne suburb of Frankston,[5] with right-turning vehicles instead turning left then making a U-turn. (Traffic in Australia drives on the left.)
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.[2] 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.[2] Consequently, the timing of traffic signals along a highway featuring Michigan lefts 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.[2] Finally it has been shown to enhance safety to pedestrians crossing either street at an intersection featuring Michigan lefts, 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.[2]
There are several reasons why other states have yet to adopt the Michigan Left as a normal intersection geometry:
- Confusion. Since the scheme is rare outside of Michigan, it can be confusing to visitors expecting to be able to turn left from the left lane.[2]
- Extra Land. Depending on the width of the existing median, extra land may be needed for large vehicles to make the U-turn because their minimum turning radius is greater than the width of the median; essentially the larger vehicle must cross both oncoming lanes to get to the extra roadway added for this purpose (see diagram to the right).
- Access to business. It may be harder to access local businesses.[2]
See also
References
- ^ North Carolina State University, Unconventional Left-Turn Lanes Reduce Traffic Accidents, Congestion, August 1, 1999
- ^ a b c d e f g Federal Highway Administration, Alternative Intersection Treatments - Median U-Turn Crossover
- ^ http://www.ci.farmington-hills.mi.us/egov/docs/1098972815_561889.pdf
- ^ "Michigan Lefts", Michigan Department of Transportation, accessed 2008-03-31
- ^ Frankston Leader, P-turn to shut Frankston residents out of their street, March 2, 2009
External links
- The Michigan Left-Hand Turn
- Synthesis of the Median U-Turn Intersection Treatment, Safety, and Operational Benefits
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