Interstate 70 in Missouri

Crossing into Missouri on the Lewis and Clark Viaduct, I-70 immediately encounters the Alphabet Loop, a small but complex loop of freeways with all of its exits having a number of 2 and a letter suffix that uses the entire alphabet (except I, O, and Z).[2] I-70 becomes concurrent with I-35 once it enters into the Loop. Both interstates maintain the concurrency until they approach the northeastern corner of the Loop.[3] Back at the northwest corner, US 169 splits off to the north, leaving four routes concurrent with each other. There is a large interchange with Route 9 in the Loop's northeastern corner.[4] At that corner, US 24 splits to the east, I-29 ends, and US 71 joins.[5]

Once it leaves I-35, I-70 turns south, with interchanges to more roads. At the southeastern corner, I-70, US 40, US 71 all exit the Loop. I-70 and US 40 split off to the east, and US 71 continues south. I-670 ends at the alignment.[6] Not long after they usurpt that alignment, I-70/US 40 turn southeast. US 40 departs from I-70 at exit 7A.[7] I-70 then interchanges with I-435, the beltway around Kansas City.[8]

While passing through Kansas City, I-70 is known as the "George Brett Super Highway", named after former Kansas City Royals third baseman and Baseball Hall of Fame member George Brett. The Truman Sports Complex, which houses the Royals' and Chiefs' stadiums, is located adjacent to the I-70/I-435 interchange.

I-70 in Saline County

East of I-435, I-70 continues east through Independence, passing a busy cloverleaf interchange at I-470.[9] The highway then continues with six lanes to the rapidly growing suburb of Blue Springs, where the roadway narrows to four lanes (two each direction) at Route 7.[10] I-70 remains at this width until just west of the intersection with I-64/US 40/US 61 in Wentzville, over 170 miles (270 km) away.

East of Blue Springs, I-70 takes on a rural highway as it leaves Jackson County. The highway remains this way for the next 100 miles (160 km), going through gently rolling terrain while it meets US 65 at a cloverleaf interchange and finally crossing the Missouri River at Rocheport just west of where it reaches the mid-sized college town of Columbia in the center of the state.[11] Through Columbia, the highway is lined with restaurants and hotels and can get congested during University of Missouri sporting events. The highway leaves Columbia after an exit with St. Charles Road on the east end of town.[12] East of Columbia, I-70 has an interchange with US 54 at Kingdom City, Route 19 at New Florence, and Route 47 at Warrenton. Then, it continues through more gently rolling terrain until it reaches Wentzville, where it meets I-64/US 61. Here, US 40 departs from I-70. It then expands to three lanes each direction to St. Louis.

I-70 west of St. Louis; shown here is rush-hour traffic congestion. Since this photograph was taken, this section has been widened to 4 lanes in each direction.

East of Wentzville, I-70 passes through the bedroom community of Lake St. Louis, then the growing towns of O'Fallon and St. Peters, and finally the historic city of St. Charles.

It crosses over the Missouri River one last time on the Blanchette Memorial Bridge, which is actually made up of two bridges: the westbound span built in the late-1950s and refurbished in 2013 and the eastbound one completed in the late-1970s.

Traffic volume increases as I-70 enters St. Louis County, requiring more lanes. There are as many as 13 lanes at one point. The section of I-70 from Fifth Street in St. Charles to I-270 is among the busiest section of highway in the state, with AADT counts approaching 165,000 in 2005.

I-270 draws much of the traffic, so I-70 continues east through Bridgeton with only six lanes. After interchanges with Route 180 (St. Charles Rock Road) and US 67 (Lindbergh Boulevard), it passes on the southern edge of Lambert–St. Louis International Airport and through several bedroom communities – including Edmunson, Berkeley, Ferguson, and Jennings – and crossing I-170 in the process.

As it finally enters the city of St. Louis, motorists encounter what are signed as the "Express Lanes", known by MoDOT as the "reversible lanes".[13] Two lanes in the middle of the freeway are separated from the eastbound and westbound lanes by Jersey barriers. Due to traffic pattern changes caused by the I-64 reconstruction, the lanes travel eastbound all day. MoDOT regularly monitors traffic patterns of this stretch of I-70 and will adjust the express lane traffic patterns accordingly.[13] These lanes have no entrance or exit ramps, except at the ends. They extend approximately 8 miles (13 km) from near Union Boulevard to just north of downtown.

Just before it enters downtown St. Louis, I-70 turns to the east to cross the Stan Musial Veterans Memorial Bridge, which redirects the highway's traffic away from the congested Poplar Street Bridge two miles (3.2 km) to the south. This 2-mile stretch of former I-70 is now an extension of I-44.