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Michigan Lefts

 

photo of a Michigan Left signWhat is a Michigan Left?

Michigan Lefts are a type of turn common in our state. Where a Michigan Left is in place, left turns at the intersection are not allowed. Instead, to turn left, you must drive straight or turn right, then make a U-turn at a median crossover, guided by sign like the one at right. Michigan Lefts have been part of Michigan roadways since at least the late 1960s.

Why has the State of Michigan adopted these?

Research and experience have shown that the Michigan Left relieves congestion; it increases safety by reducing the number and severity of crashes. Whenever MDOT plans work on a boulevard (divided roadway), engineers will consider incorporating Michigan Lefts.

How do Michigan Lefts compare in efficiency to conventional intersections?

They provide 20 to 50 percent greater capacity than direct left-turns. They reduce average delays to left-turning vehicles and through-traffic.

What is the largest vehicle that can use a Michigan Left crossover?

This depends on the space available, cost, and local conditions. MDOT designs crossovers and medians with the local traffic in mind. In major commercial or industrial areas, crossovers need to accommodate large trucks (74-foot overall length, 45' turning radius). We accomplish this by building a wider median or by providing "truck loons" (paved areas on the outside edge of the roadway across from the crossovers). In residential or light commercial areas, typical crossovers are designed for a vehicle 55 feet long with a 45' turning radius.

What about out-of-state drivers who are not used to Michigan Lefts?

MDOT has not done any specific studies on this issue. However, no problems have been evident to date, nor have we received many complaints from non-residents. Non-Michigan drivers do not appear to have significant difficulties with Michigan Lefts.

What about pedestrians?

Michigan Lefts increase pedestrian safety. Divided roadways are safer for pedestrians in general, since they can cross one direction of the roadway at a time and wait at the median to safely finish crossing. Where direct left turns are prohibited, the traffic signal can remain green for pedestrian crossings longer.

photo of an intersection with a  Michigan Left

What's the effect on crashes?

On roadways where crossovers and Michigan Lefts have been added, crashes have been reduced 30 to 60 percent overall. The greatest reductions are in rear-end and head-on crashes during left-turns (60 to 90 percent reduction) and right-angle crashes (60 percent reduction). Slight increases are noted for two other crash types. Non-left-turn rear-end crashes increase by approximately 25 percent, and fixed-object crashes increase by approximately 20 percent.

Do winter weather conditions affect crashes at Michigan Lefts?

Not really. However, it is thought that the 20 percent increase in fixed-object crashes is due largely to vehicles sliding into the curb and gutter at the crossovers because of snowy or icy conditions.

How does MDOT determine where to build a Michigan Left?

Engineers study the crash history and traffic at major intersections along a roadway. Indirect left turns can be built on divided roadways with any number of lanes (i.e., 4-lane, 6-lane, or 8-lane).

Michigan Lefts are most often used in urban situations where congestion and crashes are more common. They are not used on freeways or limited-access roads of any kind. U-turns and other movements through freeway medians are strongly discouraged.

How far apart does MDOT build Michigan Lefts?

Ideal spacing is between one quarter and three quarters of a mile. The actual distance is determined by the locations of major cross roads and driveways. Intersections with traffic signals need to be far enough apart that vehicles lined up to turn will not cause significant congestion.

What are the maximum/minimum traffic volume requirements for the Michigan Left?

There are no absolute requirements. Michigan Lefts increase capacity and safety on divided roadways at all volumes. Indirect left-turns have been used on state routes with average traffic volumes (ADT) of between 10,000 and 100,000 vehicles per day.

 




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