Interstate 170

Interstate 170
State	MO
Route	170
Length mi	2.88
Established	1965
Direction a	South
Terminus a	Interstate 64/U.S. Route 40/Interstate 55 (St. Louis)
Direction b	North
Terminus b	Interstate 70 (St. Louis)
Counties	St. Louis County

Interstate 170 is a short auxiliary Interstate Highway in the United States Interstate Highway System serving the inner suburbs of St. Louis. The route forms a north–south connector between major radial routes near downtown St. Louis County and provides urban access to neighborhoods such as Ladue, Wellston, and University City. Originally planned as part of a more extensive urban freeway network, it remains one of the shortest signed three-digit Interstates in the Midwestern United States.

Route description

The highway begins at a multilayered interchange with Interstate 64, U.S. Route 40, and Interstate 55 near the southern edge of Downtown St. Louis. From there it proceeds north as a six-lane freeway through a corridor adjacent to Delmar Loop, Forest Park-DeBaliviere, and the St. Louis County Department of Transportation. Interchanges link to Kingshighway Boulevard, Manchester Road, and Olive Boulevard, providing access to institutions such as Washington University in St. Louis, Saint Louis University Hospital, and the Missouri Botanical Garden. The route crosses municipal boundaries including University City, Clayton, and Brentwood, terminating at an elevated junction with Interstate 70 near the Gateway Arch National Park view corridors and industrial zones abutting the Missouri River.

History

Planned during the postwar era of Interstate expansion under the Federal-Aid Highway Act of 1956, the alignment reflects the Urban Renewal and freeway revolts that shaped many mid-20th-century projects. Early corridor proposals envisaged a longer north–south expressway connecting to the Chain of Rocks Bridge approaches and linking with Interstate 64 and Interstate 270. Opposition from civic groups including Citizens for Responsible Development and neighborhood associations in University City curtailed extensions northward, while state agencies such as the Missouri Department of Transportation adjusted plans to the existing right-of-way. Construction phases in the 1960s and 1970s paralleled contemporaneous projects like Interstate 44 upgrades and the rebuilding of U.S. Route 61 spurs. Subsequent modifications addressed safety concerns raised after incidents near Forest Park and during major events like the 1984 Republican National Convention and 1994 World Cup activities in the region.

Exit list

The signed interchanges along the route provide access to regional arterials and landmarks. Major junctions include connections to Interstate 64/U.S. Route 40/Interstate 55 at the southern terminus, an interchange serving Kingshighway Boulevard, an intermediate exit for Manchester Road providing routes to Brentwood Promenade and St. Louis Galleria, and a northern terminus at Interstate 70 with ramps toward downtown St. Louis. Auxiliary ramps facilitate movements to West Florissant Avenue, Skinker Boulevard, and local connectors to Forest Park institutions including St. Louis Art Museum and Saint Louis Zoo. Several exits have been reconfigured over time to accommodate traffic engineering projects led by the Metropolitan St. Louis Sewer District and the Regional Transit Authority of St. Louis.

Future and proposals

Periodic proposals have resurfaced to extend or modify the corridor to improve regional mobility and multimodal access. Proposals include an extension to reconnect with Interstate 270 or to tie into the North-South Corridor concepts studied by the East-West Gateway Council of Governments. Other ideas involve converting portions into a boulevard with enhanced Metrolink or bus rapid transit lanes to serve growth areas such as Ladue and Creve Coeur. Funding discussions have involved agencies like the Federal Highway Administration, the Missouri Department of Transportation, and county transportation planners; constraints include community opposition, right-of-way acquisition near Skinker–DeBaliviere, and historic preservation concerns tied to Forest Park vista protections.

Traffic volumes and tolling

Average annual daily traffic (AADT) counts on the corridor reflect urban commuter patterns, peaking during University City and downtown event periods. Counts have been influenced by commuting flows to employment centers like Downtown St. Louis, Clayton legal and corporate complexes, and retail destinations including St. Louis Galleria. Several studies by the Missouri Department of Transportation and the East-West Gateway Council of Governments evaluated congestion mitigation, with models considering ramp metering, managed lanes, and limited tolling. Tolling proposals faced legal and political hurdles, including regulatory reviews by the Federal Highway Administration and local opposition from organizations such as Citizens for Humane Transportation.

Auxiliary and related routes

The route functions as an auxiliary spur of Interstate 70 and interacts with other numbered routes including Interstate 64, Interstate 55, and U.S. Route 40. Related infrastructure projects include interchange reconstructions associated with Interstate 44 and coordinated corridor studies with Interstate 170 (St. Louis) Commission stakeholders and regional planners at the East-West Gateway Council of Governments. Other parallel and connector facilities include Missouri Route 340 and local arterials such as Olive Boulevard and Manchester Road serving suburban mobility.

Category:Interstate Highways in Missouri Category:St. Louis County, Missouri