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; 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. 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.
Recent construction 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. ==Southern extension==