U.S. Route 40 (US 40) in the state of Missouri is a U.S. highway that runs from Kansas City to St. Louis.

US 169 exits the freeway north to the Buck O'Neil Bridge and I-35 joins with the remaining three routes.

[1][2] For 77 miles (124 km), US 40 runs along I-70 through rural areas, meeting US 65 at Marshall Junction as well as multiple state highways in different locations.

US 40 eventually leaves the freeway to serve downtown Boonville, running concurrently with I-70 Bus.

[1][2] US 40 continues to run along I-70 through rural areas between Columbia and Wentzville; the freeway, at one point, meets US 54 in Kingdom City.

After crossing the river, the freeway serves the Spirit of St. Louis Airport in Chesterfield.

Next to the I-170 interchange in Richmond Heights, drivers can get on the Brentwood I-64 station on the Blue Line.

The freeway then crosses above the Mississippi River via the Poplar Street Bridge to enter Illinois.

[4][5] US 40 originally ran through St. Charles, but was rerouted southward closer to its current alignment in 1941.

[27][28] From 2007 to 2010, MoDOT reconstructed a portion of I-64/US 40 (dubbed "The New I-64" project) from Spoede Road to Kingshighway Boulevard.