Interstate 170 Missouri

Overview

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.

Mileage by State

Missouri

11.17 mi

Data Sources

December 31, 2021 Interstate Route Log and Finders List

History

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

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 built.

North End  ‐ Hazelwood, MO

North at

Exit 9C to Hanley Road is the final mainline off-ramp from I-170 north. Traffic partitions for I-270 west to Bridgeton and east to Bellefontaine Neighbors in one mile. 10/16/04

East at

Interstate 270 and U.S. 67 converge at what was a cloverleaf interchange (Exit 25) just prior to I-170. The loop ramp for Lindbergh Boulevard north was removed by 2013. 05/03/12

West at

Succeeding ramps depart from Interstate 270 west for Graham Road / N Hanley Road to the cities of Hazelwood and Florissant and I-170 south to STL Airport over the next mile. 05/24/18

South End  ‐ Brentwood, MO

South at

I-170 angles southeast through Clayton, 0.75 miles ahead of I-64/U.S. 40. Succeeding lane drops occur over the next half mile for Brentwood Boulevard. 05/04/12

East at

I-64/U.S. 40 navigate through a series of S-curves leading to the south end of I-170 at Exit 31 A. 05/24/18

West at

Exit 31B partitions with I-64/U.S. 40 west to both S Hanley Road and Brentwood Boulevard for the cities of Richmond Heights and Brentwood. The freeway mainline proceeds west to the systems interchange with I-170 north. 04/13/13

South End – Past Views

Past Views Gallery (Tap to Expand / Collapse Section)

South at

The end sign for I-170 at Exit 1D was amended from one to a half mile. The ramps for I-64 previously separated from I-270 three quarters of a mile south of Brentwood Boulevard. They split a quarter mile further north now. Photo by Brian Dowd (08/23/02).

East at

Prior to the New I-64 reconstruction project finished in 2009, a number of low clearance overpasses spanned the freeway east into St. Louis. The initial guide sign for I-170 was mounted on the McKnight Road overpass. Photo by Brian Dowd (06/02).

West at

A substandard six-ramp parclo interchange previously joined I-64/U.S. 40 with Hanley Road. Part of the New I-64 reconstruction project, work rebuilt this exchange into a split diamond interchange, with frontage roads extending past I-170 to Brentwood Boulevard. Photo by Rich Piehl (12/00).

References

1. Interstate 170. Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Interstate_170
2. Dowd, Brian.