Missouri Route M (Jefferson County)

Route M
Route M highlighted in red
Route information
Maintained by MoDOT
Length	7.478 mi[1] (12.035 km)
Existed	c. 1953–present
Major junctions
West end	Route 21 / Route MM near Otto
Major intersections	I-55 near Barnhart
East end	US 61 / US 67 near Barnhart
Location
Country	United States
State	Missouri
Counties	Jefferson
Highway system
Missouri State Highway System Interstate US State Supplemental

Route M is a short arterial highway in Jefferson County, Missouri. It is a major east–west route which connects Route 21 to Interstate 55. For the majority of its length, Route M is a four lane divided highway with limited access. At its junction with Interstate 55, Route M becomes an undivided two lane road until its eastern terminus at U.S. 61/67. Route M was rerouted to its present location in the late 1990s after traffic became too great for the original road to handle. The original route is now known as Old Route M.