Located in St. Louis County west of the city of St. Louis, Interstate 170 is the Inner Belt Expressway. I-170 is a commuter route serving suburban cities from Ladue and Clayton north to University City, Overland and Berkeley. The Inner Belt Expressway connects with I-270, St. Louis Lambert International Airport (STL) and the adjacent Boeing plant to the north and I-64/U.S. 40 at Brentwood and Richmond Heights to the south.
Constructed during the 1960s, Interstate 170 was previously designated as Missouri Route 725. Route 725 was a part of a planned inner beltway that never made it to full fruition.1 The Federal Highway Administration (FHWA) approved adding 3.0 miles of the Inner Belt Highway, from I-70/Route 725 north to I-270, to the Interstate System on April 28, 1978 under the provisions of 23 U.S.C. 103(e)(1). 1979. The American Association of State Highway and Transportation Officials (AASHTO) approved the establishment of Interstate 170 on June 29, 1978. Expected to open by 1982, the application cited that I-170 will:
Facilitate North-South traffic movement between existing Interstate Routes 70 and 270 which are presently experiencing difficulties with this interchanging traffic.
The Missouri State Highway Commission subsequently applied for a southern extension of Interstate 170 over Route 725 to U.S. 40 at Richmond Heights.
On behalf of the Chief Engineer, Leland D. Fletcher, Assistant to the Chief Engineer – Planning and Design, advised the Commission that since the recent addition to the Interstate System of I-170 from I-70 to I-270, it was desirable to consider extending the I-170 marking over present Route 725 from I-70 southerly to U.S. Route 40 to provide a continuous single marking for the freeway facility.
The state advised that the extension would not incur additional responsibility for Federal funding and that the route would not be marked until the 3.03 mile long section under construction from I-70 and Page Avenue was completed. AASHTO approved the 7.7 mile long addition on June 25, 1979. The FHWA previously concurred that this section of Route 725 was a logical addition or connection to the Interstate System on June 15, 1979. 4.2 miles of Route 725 were open to traffic south from Page Avenue at the time.
Originally, the Inner Belt Expressway was proposed to continue further into the southern part of St. Louis County. However by the late 1990s, residents of neighborhoods in the project path voiced opposition. Ultimately plans were dropped and six months later, the Missouri Department of Transportation (MoDOT) sold the acquired 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. Additionally the overpass carrying I-270 across Hanley and Graham Roads was replaced and widened to ten overall lanes.2