U.S. Route 40 in Missouri

U.S. Route 40 (US 40) in the state of Missouri is a U.S. highway that runs from Kansas City to St. Louis. Outside of Greater St. Louis, much of the route either parallels or runs along I-70. East of Wentzville in Greater St. Louis, the route runs along I-64.

Route description
US 40, along with I-70, US 24, and US 169, enters Kansas City via the Intercity Viaduct. US 169 exits the freeway north to the Buck O'Neil Bridge and I-35 joins with the remaining three routes. At the interchange with I-29 and US 71, I-70, US 24, and US 40 turn south while I-35 turns north. At I-670, I-70, US 24, and US 40 turn east while US 71 continues south toward I-49. In East Side, US 40 leaves I-70 before meeting I-435/US 24. Shortly after I-435, US 40 runs along or parallels the Kansas City–Independence line. Between I-470 and Blue Springs, the two roadways splits. At Grain Valley, US 40 rejoins I-70.

For 77 mi, 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. and Route 5 in the process. As the road approaches downtown, I-70 Bus. turns southeast while US 40 and Route 5 turns north, both running along Route 87. After leaving downtown and crossing above the Missouri River, Route 87 and then Route 5 leaves northward from US 40. US 40 parallels the Missouri River before reaching Rocheport; the route then parallels I-70. US 40 reenters the freeway just after Midway.

I-70/US 40 runs north of downtown Columbia. The freeway serves US 63 via a connector road, located east of the US 63 freeway.

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. In Wentzville, at the Greater St. Louis area, US 40 leaves I-70 to enter I-64/US 61. US 40, along with I-64 and US 61, then crosses the Missouri River again, this time via the Daniel Boone Bridge. After crossing the river, the freeway serves the Spirit of St. Louis Airport in Chesterfield. At the Frontenac–Ladue line, US 61 leaves the freeway to enter south along US 67 (Lindbergh Boulevard). Next to the I-170 interchange in Richmond Heights, drivers can get on the Brentwood I-64 station on the Blue Line. Just after entering St. Louis proper, I-64/US 40 pares through the southern part of Forest Park. The freeway then becomes a double-decker twice: from Vandeventer Avenue to Compton Avenue and from 14th Street (near the Gateway Transportation Center) to an interchange with I-44/I-55. I-55 merges with I-64/US 40 near Gateway Arch. The freeway then crosses above the Mississippi River via the Poplar Street Bridge to enter Illinois.

History
US 40 was formed in 1926. In Missouri, it ran from Kansas City to St. Louis roughly along its current alignment except in the St. Louis area. US 40 originally ran through St. Charles, but was rerouted southward closer to its current alignment in 1941.

Daniel Boone Expressway
The first section of present-day I-64/US 40 between Skinker Boulevard and Vandeventer Avenue opened in 1937. Originally called the Express Highway, it was then renamed to Red Feather Highway in 1948.

The Daniel Boone Expressway was established in 1938 from the Daniel Boone Bridge above the Missouri River to Lindbergh Boulevard. The expressway later extended eastward to Brentwood Boulevard in the 1940s. In 1959, the expressway was extended east from Brentwood to the Red Feather Highway, of which the latter highway became part of the Daniel Boone Expressway. In 1965, the expressway was extended to a pair of now-demolished connector ramps (part of a now-canceled expressway) east of Jefferson Avenue. The Poplar Street Bridge and the double-decker expressway east of 8th Street opened in 1967, which led to the realignment of US 40 from the Veterans Bridge to the newly-opened freeway bridge. The remaining double-decker section in downtown was finished by 1970.

In 1987, I-64 was extended west from the I-55/I-70/US 40 interchange in East St. Louis, Illinois, to I-270 in Town and Country via US 40 with a possibility of extending further west to I-70 in Wentzville via US 40/US 61. In the early 2000s, I-64 was extended west to Route 94. In the early 2010s, I-64 was extended to I-70 in Wentzville.

Reconstruction
The Daniel Boone Bridge originally had only one bridge carrying two lanes of traffic (one in each direction). In 1989, a second bridge was built to carry four lanes of eastbound traffic to accommodate an increasing amount of traffic attributed to population growth. The old bridge was reconfigured to serve three lanes of westbound traffic. However, due to the deterioration and the substandard lane configuration of the old bridge, a new bridge was built from 2013-2015 to the west of the 1989 bridge. The new bridge opened in 2015 for eastbound traffic, whereas the 1989 bridge reversed direction to serve westbound traffic. The 1937 bridge was demolished in 2016.

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.