The Blanchette Memorial Bridge carries Interstate 70 across the Missouri River between St. Louis County and St. Charles County, Missouri. It is formed from a pair of twin cantilever bridges and opened in 1959, with a second bridge opened in 1979. At the bridge's crossing, the Missouri River reaches an average depth of 45 feet. It is the area's busiest bridge, handling an average of 165,000 vehicle transits per day. Construction of the first interstate highway project (under provisions of the Federal-Aid Highway Act of 1956) started west of the bridge's present location.

A sign commemorating the site of the nation's first interstate project stands next to Interstate 70 just east of the Missouri Route 94/First Capitol Drive overpass.

In 1979, a second span was opened due to the fact that the two laned configuration had become obsolete. The bridge was then named for French Canadian fur trader and hunter Louis Blanchette, who founded St. Charles as a post along the Missouri River; the village was the first European settlement along this waterway.

Major rehabilitations for the westbound span have been addressed to MoDot in the late 2000s. The project started with the closure of the westbound span on November 4, 2012. During the closure, westbound traffic was diverted to the freeway's east side, for three narrow lanes in each direction. The westbound bridge's old superstructure was demolished in two explosions, with the first taking place on November 18, 2012. The second and final blast was on December 4, 2012. Construction of the replacement bridge started in spring 2013, and the new bridge opened more than two months ahead of schedule in August 2013. The entire project was completed in 2014.

In spring 2020, a repair project began on both bridges, with rehabilitation of the westbound span being completed in fall 2020 and the eastbound bridge in 2022.

• Transport portal
• Engineering portal
• United States portal
• List of crossings of the Missouri River