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A typical Michigan left setup.

A median U-turn crossover or median U-turn,[1][2] is an at-grade intersection design which replaces each left turn with a permutation of a U-turn and a right turn. The design is also known as a Michigan left due to its frequent use along Michigan roads and highways since the late 1960s,[3] and a MDOT animation is available here. The design is also sometimes referred to as a boulevard turnaround.[4]

Contents

Description

The design occurs 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 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.

Locations

The first use of the design by the 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 the median u-turn cross over 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.)

The design has been proposed in Toronto to relieve motorists who wish to make a left-turn on roadways which will contain a proposed streetcar line by the Transit City project.

In Mexico, Guadalajara has a grade-separated variation of this setup in the intersection of Mariano Otero avenue and the Manuel Gómez Morín beltwaymap. 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.

Applicable traffic studies

Two versions of signs posted along an intersecting road or street at an intersection. Top: most commonly used; Bottom: lesser-used variant.

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 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.[2] Finally 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.[2]

However, other states have yet to adopt the design as a normal intersection geometry:

Stylized depiction of the design in Grand Haven, Michigan at US 31 and Robbins Rd (rotated 90 degrees), showing additional land necessary to make a turn on a narrow median. 43°2′40.18″N 86°13′12.57″W / 43.0444944°N 86.2201583°W / 43.0444944; -86.2201583 (US-31 at Robbins Rd., Grand Haven, MI)
  • 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]
  • Time. Drivers doing a left turn must pass twice through a traffic light, thus increasing greatly the time it takes to make a left turn.

See also

References

  1. ^ North Carolina State University, Unconventional Left-Turn Lanes Reduce Traffic Accidents, Congestion, August 1, 1999
  2. ^ a b c d e f g Federal Highway Administration, Alternative Intersection Treatments - Median U-Turn Crossover
  3. ^ "Michigan Lefts", Michigan Department of Transportation, accessed 2008-03-31
  4. ^ http://www.ci.farmington-hills.mi.us/egov/docs/1098972815_561889.pdf
  5. ^ Frankston Leader, P-turn to shut Frankston residents out of their street, March 2, 2009

External links

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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, and rare anywhere else in the United States. The Michigan left has been a part of Michigan roadways since at least the late 1960s[4], and a MDOT animation is available here.

Contents

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.

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: , Michigan at US 31 and Robbins Rd (rotated 90 degrees), showing additional land necessary to make a turn on a narrow median.]]

  • 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

  1. ^ North Carolina State University, Unconventional Left-Turn Lanes Reduce Traffic Accidents, Congestion, August 1, 1999
  2. ^ a b c d e f g Federal Highway Administration, Alternative Intersection Treatments - Median U-Turn Crossover
  3. ^ http://www.ci.farmington-hills.mi.us/egov/docs/1098972815_561889.pdf
  4. ^ "Michigan Lefts", Michigan Department of Transportation, accessed 2008-03-31

External links


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