Route M was rerouted to its present location in the late 1990s after traffic became too great for the original road to handle.

At Barnhart, the intersection with Marriott Parkway connects Interstate 55 traffic with gas stations and retail stores.

Turnarounds built short distances east and west of the intersection allow access to and from the westbound lanes.

[3] On December 7, 2009, access to southbound I-55 was closed when MoDOT began a project to rebuild the interchange.

Southbound access to I-55 from Route M, which had featured a loop ramp, was being relocated to a new roundabout on Metropolitan Boulevard, which will also connect to a park and ride.