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Rant: Why aren't Michigan lefts the standard on new arterial streets?

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renegade:

--- Quote from: kernals12 on July 16, 2021, 12:29:35 PM ---Left turns are the bane of traffic engineers, ruining the otherwise perfect signal precession that could guarantee drivers green lights.

But in the 60s, Michigan solved that problem by incorporating u turns into the medians of divided highways to all for left turn movements while prohibiting them from the main intersection


Studies have shown they result in enormous improvements in safety and traffic flow. Because they also require the use of a wide median, they offer space for landscaping and stormwater drainage.

Imagine if this had become the standard design for new arterial streets all over the country, and perhaps the world. Think of all the time, money, and lives saved.

Why the f*ck aren't these everywhere?

--- End quote ---
Michigan Lefts are a pain ... trust me on this:  You don't want them everywhere.

paulthemapguy:

--- Quote from: kernals12 on July 16, 2021, 12:29:35 PM ---enormous improvements in safety and traffic flow
--- End quote ---

*In studies where flow is measured amongst thru traffic only.  These traffic studies often make the assumption that the majority of traffic at an intersection will proceed straight, rather than turning.  This is NOT a safe assumption to make at an impressive percentage of major intersections.

Another issue- Michigan lefts require a wide enough median to facilitate a left turn.  If trucks are involved, that requires an even wider space.  Even in the illustration above, the median appears to be about 36 feet wide.  That's a wide enough corridor to put in three traffic lanes!  Two 12-foot lanes in each direction, plus 36 feet in the median, and say, 20 feet on either side of the road, amounts to 104 feet of right-of-way.  You need a corridor at least 100 feet wide to make this happen.  Michigan planned their roads to be this way from the get-go; good luck retrofitting this scheme somewhere else.

kernals12:

--- Quote from: paulthemapguy on July 16, 2021, 02:17:37 PM ---
--- Quote from: kernals12 on July 16, 2021, 12:29:35 PM ---enormous improvements in safety and traffic flow
--- End quote ---

*In studies where flow is measured amongst thru traffic only.  These traffic studies often make the assumption that the majority of traffic at an intersection will proceed straight, rather than turning.  This is NOT a safe assumption to make at an impressive percentage of major intersections.

Another issue- Michigan lefts require a wide enough median to facilitate a left turn.  If trucks are involved, that requires an even wider space.  Even in the illustration above, the median appears to be about 36 feet wide.  That's a wide enough corridor to put in three traffic lanes!  Two 12-foot lanes in each direction, plus 36 feet in the median, and say, 20 feet on either side of the road, amounts to 104 feet of right-of-way.  You need a corridor at least 100 feet wide to make this happen. Michigan planned their roads to be this way from the get-go; good luck retrofitting this scheme somewhere else.

--- End quote ---

Notice how the title says new arterials.

Max Rockatansky:
But itís still a factor.  It probably is a more difficult sell to plan an arterial road with a huge median versus one that follows a more conventional width.  That wide median means less room for development along the arterial highway.

kernals12:

--- Quote from: renegade on July 16, 2021, 02:10:41 PM ---
--- Quote from: kernals12 on July 16, 2021, 12:29:35 PM ---Left turns are the bane of traffic engineers, ruining the otherwise perfect signal precession that could guarantee drivers green lights.

But in the 60s, Michigan solved that problem by incorporating u turns into the medians of divided highways to all for left turn movements while prohibiting them from the main intersection


Studies have shown they result in enormous improvements in safety and traffic flow. Because they also require the use of a wide median, they offer space for landscaping and stormwater drainage.

Imagine if this had become the standard design for new arterial streets all over the country, and perhaps the world. Think of all the time, money, and lives saved.

Why the f*ck aren't these everywhere?

--- End quote ---
Michigan Lefts are a pain ... trust me on this:  You don't want them everywhere.

--- End quote ---
Try experiencing life without them.

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