Interstate 170 is the Inner Belt Expressway in the St. Louis County, west of the city of St. Louis. This north-south freeway connects I-270 to Interstate 64 & U.S. 40 at the cities of Brentwood and Richmond Heights. The Inner Belt Expressway is heavily traveled, servicing suburban cities, St. Louis Lambert International Airport (STL) and the adjacent Boeing plant as a commuter route.
Interstate 170 was originally designated as Missouri 725 when constructed during the 1960s. The route was a part of a planned inner beltway that never made it to full fruition.1 I-170 was established by AASHTO on June 29, 1978 from I-70 / Missouri 725 northward to I-270 over the newly constructed freeway. AASHTO approved the extension of Interstate 170 southward from Missouri 725 to U.S. 40 at Richmond Heights on June 25, 1979.
Originally, Interstate 170 was supposed to continue south into the southern part of St. Louis County. However by the late 1990s, the neighborhood just to the south voted to kill that plan, as they wanted to keep their community intact. Six months later, MoDOT sold the right-of-way to a developer, which built a shopping center.2
The north end of Interstate 170 was reconstructed from the early 2000s to 2004. The project reconfigured the directional T interchange with I-270 to eliminate three left exits between the two freeways. Additionally the overpass carrying I-270 across Hanley and Graham Roads was replaced and widened to ten overall lanes.2
The “New I-64” project from 2000 to 2009 included a major overhaul of the exchange joining the south end of I-170 with I-64 & U.S. 40 at Richmond Heights. The previous interchange lacked a direct connection from I-64 east to I-170 north, requiring motorists to navigate along Brentwood Boulevard to either Eagar Road or Galleria Parkway to access the Inner Belt Expressway northbound.2 A systems interchange with high speed ramps for all movements was eventually built.