Michigan left
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A Michigan left, sometimes known as a median U-turn<ref>North Carolina State University, Unconventional Left-Turn Lanes Reduce Traffic Accidents, Congestion, August 1, 1999</ref> or median U-turn crossover,<ref name=FHWA>Federal Highway Administration, Alternative Intersection Treatments - Median U-Turn Crossover</ref> is an automobile traffic maneuver in which a unidirectional U-turn and a right turn replace a prohibited left turn. The term comes from the fact that the arrangement is quite common along Michigan roads and highways, and extremely rare anywhere else in the United States.
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[edit] Description
Michigan lefts occur at intersections where at least one road is a divided highway or boulevard. Left turns onto the divided highway are prohibited. Instead, drivers on roads that cross the highway are directed to turn right. Within a 1/4 mile (400 m), they queue into a designated U-turn 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.
[edit] 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.
The Michigan left is also common in New Orleans, Louisiana[citation needed], in South Korea[citation needed], and in Taiwan (see the accompanying sign for examples).
[edit] Advantages and disadvantages
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.
[edit] Advantages
- Safety — potentially provides 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<ref name=FHWA/>
- Reduced travel times — Reduces the number of different traffic light phases, 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.<ref name=FHWA/>
- More options for turning — At intersections where both roads have Michigan Lefts, there is more than one way to turn left. For example it is possible to either turn right at the intersecting road, and use the U-turn to go left, or go past the intersecting road, use the U-turn on the original road, and make a right on the intersecting road. This is very useful when trying to avoid traffic lights provided there isn't a "No turn on red" sign. It also allows for an alternate path in case of a traffic-blocking incident.
- Cost — U-turn lanes are often already present on divided highways to provide for access to businesses in the opposing direction. Hence the addition of the Michigan left turnaround is essentially free.
- Enhanced progression — 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. Thus, traffic progression through the timed signals in enhanced, contributing further to the reduction of travel times and the increased capacity of those roadways.<ref name=FHWA/>
- Fewer threats to pedestrians — Pedestrians crossing either street at an intersection featuring Michigan lefts only encounter through traffic and vehicles making right turns. The left-turning movement, having been eliminated, removes one source of potential vehicle-pedestrian conflict. However, the major roadway typically has a wider cross section, making said crossing longer.<ref name=FHWA/>
[edit] Disadvantages
- Confusing — 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.<ref name=FHWA/>
- Inconsistent — not all intersections use the system, so drivers approaching an unfamiliar intersection do not necessarily know whether to be in right or left lane, although signage is generally placed in advance of intersections requiring such a maneuver.[original research?]
- Land use — Depending on the width of the existing median, extra land may be needed for large vehicles to make the U-turn. Additionally it may be harder to access local businesses.<ref name=FHWA/>
- Cycling - the increased number of right turns means more conflicts with bicycle lanes.<ref name=FHWA/>
- Stress — drivers may need to quickly move across several lanes of traffic when getting into or out of the U-turn, although if traffic does not permit, typically another U-turn is available within less than a mile. The need to "quickly" move across several lanes is negated, however, when making the right turn on a green light, whereby all traffic on the cross-street is stopped.
- Expense — On high traffic roads, Michigan lefts may require an additional pair of traffic lights at each of the turnarounds. This is offset, however, by the much simpler traffic signal set-up at the primary intersection, largely due to the removal of the left-turn movement and all dedicated signals and left-turn lane allowances.[original research?]
- Visibility — Drivers inching up in the right lane of a Michigan Left may block the visibility of drivers attempting to make a turn from the left lane. The problem also sometimes happens when there is a backup in an opposing Michigan Left.[original research?]
- Safety – while reducing collisions in the intersection, traffic has to join the opposing traffic flow at the U turn in the fast lane, unless as mentioned above, a signal is put in place to allow for traffic to complete their turn.
[edit] Trivia
Despite the fact that in recent years many lesser-used intersections (particularly) in Southeastern Michigan have been upgraded to have Michigan lefts due in part to increases to traffic flow, there are still a few intersections there that, despite having had the Michigan left requirement for years, have at least one movement that does not require the Michigan left. Among them are:
- Fort St. and West Rd. in Trenton - Turning onto westbound West Rd. from northbound Fort St. does not require the Michigan left, but all other turns do. Reportedly, the Michigan left requirement was installed for that sometime in the late 90s, but local opposition changed it back soon after.
- Southfield Rd. and Dix Hwy. in Lincoln Park - Turning onto southbound Dix Hwy. from northbound Southfield Rd. (Southfield is technically running east-west through this area) does not require it, but all other turns do. Traffic light signage suggests that an attempt to close this loophole at one time failed to be accepted.
- Telegraph Rd. and Van Born Rd. on the border of Dearborn Heights and Taylor - This has been an interesting exception for years as turning south on Telegraph from westbound Van Born and west on Van Born from northbound Telegraph have required the Michigan left, yet turns onto eastbound Van Born from southbound Telegraph and from eastbound Van Born to northbound Telegraph have not. This is because just south of Van Born is Telegraph's junction with I-94, and formerly there were K-rails dividing the road there and no room for a turnaround of any kind regardless. Nowadays, the road there is undivided for the junction's new SPUI interchange. The intersection of Van Born and Telegraph has had left turn signals of verious types for the non-Michigan left turns.
[edit] See also
[edit] References
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[edit] External links
| Types of road junctions | |
| Interchanges (grade separated) | Cloverleaf - Diamond - Directional T - Diverging diamond Parclo - Trumpet - SPUI - Stack - Three-level diamond |
| Intersections (at-grade) | Box junction - Continuous flow - Crossroads - Hook turn - Jughandle - Michigan left Quadrant roadway - Roundabout - Superstreet - 3-way junction - Traffic circle |
