The "flex route" — scheduled to launch as early as this week — is a new system along 11 miles of U.S. 23 between Ann Arbor and Brighton. The state Department of Transportation will open and close inside median shoulders to northbound and southbound traffic using overhead electronic signs.
Cheaper to build, they are not considered true third lanes because there is no full shoulder attached.
That stretch of U.S. 23 carries 66,000 vehicles a day and is Michigan's most congested corridor outside of metropolitan Detroit. What should be a 20-minute drive in normal conditions can take up to an hour in peak periods.
Gov. Rick Snyder, who helped unveil the system on Monday at a rest stop north of Ann Arbor, called it "a winning combination for traffic management, convenience and safety." Transportation officials have said U.S. 23 is a perfect place to try flex routing because a third permanent lane in both directions is not needed at all times but instead mostly for peak commuter traffic in and out of Ann Arbor.
The next natural place to install flex routes is I-96 between Brighton and Novi, state transportation director Kirk Steudle said in September. He also mentioned U.S. 131 north and south of Grand Rapids.
A green arrow on overhead signs will say when the median shoulder can be used. A red "X'' will indicate when it is closed.
If there is a crash, motorists could save up to 50 percent of travel time when a flex route is open, according to the transportation agency. It also is expected to reduce the number of secondary crashes that occur in the aftermath of primary accidents.
The U.S. 23 flex route was created as part of a $92 million project that included replacing or repairing bridges, extending and upgrading ramps, and repaving the highway.
Flex route information: http://bit.ly/2iS7wwx
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