Interstate 170 (I-170), also known as the Inner Belt Expressway, is an 11.17-mile (17.98 km) north–south auxiliary Interstate Highway in Greater St. Louis, Missouri. I-170 connects to I-270 at its northern terminus and I-64 at its southern terminus. I-170 crosses its parent, I-70, near St. Louis Lambert International Airport.

I-170 was originally intended to provide an inner beltway within I-270 through St. Louis County extending to I-55 in the southern part of the county, commonly called South County;^[2] however, the portion of the route south of I-64/US Route 40 (US 40) was canceled due to local opposition. The portion of MetroLink's Cross County Extension south of I-64 runs roughly along the proposed alignment.^[3]

The southern portion of I-170 was built using St. Louis County funds in the 1960s through a shallow valley. It was signed as Route 725.

The southern two interchanges on I-170 (at I-64/US 40 and Galleria Parkway) were rebuilt during the first phase of the New I-64 project. The project added direct access to I-170 from eastbound I-64, eliminated access to Galleria Parkway from northbound I-170, and revised Eager Road access to and from I-170.^[4]

Proposals have been made to extend I-170 south beyond its termination at I-64/US 40, and so connect to I-55, I-270, and I-44, and to towns such as Richmond Heights, Brentwood, Maplewood, and Marlbourough. These towns currently lack direct access to the Interstates, St. Louis Lambert International Airport, South County, and to each other. Many commuters travel on slower surface streets, such as Hanley Road or River Des Peres Boulevard, raising traffic in Shrewsbury and other residential towns.^[5] These proposals had been postponed due to lack of funding.^[6]

The entire route is in St. Louis County.

• Kurumi.com: Interstate 170