I-170

I-170
Name	Interstate 170
Route	170
Type	Interstate
Direction a	South
Direction b	North
States	Missouri

I-170 is an unsigned auxiliary Interstate spur located in the north-central United States metropolitan area. It functions as a connector between suburban arterial corridors and principal radial freeways, serving commuters, freight traffic, and local access in the St. Louis region. The route interacts with multiple federal and state arteries, urban neighborhoods, and transit nodes, shaping travel patterns between municipalities, industrial districts, and commercial centers.

Route description

The corridor begins in the southern sectors where it intersects with I-64, passing close to municipal boundaries such as Creve Coeur, Webster Groves, and Richmond Heights. Proceeding northward, the alignment threads between residential districts and commercial strips near Maryland Heights, skirting institutions like Washington University in St. Louis and connecting to arterial access for Forest Park. Midway, the roadway crosses over rail rights-of-way used by BNSF Railway and Union Pacific Railroad, then reaches a major interchange with I-70, which provides links toward Kansas City and Indianapolis. Further north, the route provides ramps serving industrial corridors adjacent to the Missouri River and links to state highways such as Missouri Route 180 and Missouri Route 100. At its northern terminus, the spur integrates into the urban grid close to downtown nodes like Clayton and University City, with proximate access to regional transit operated by Metro Transit and park-and-ride facilities serving commuters bound for Downtown St. Louis.

The physical profile varies from fully grade-separated freeway sections to partial access-controlled segments adjacent to historic neighborhoods. Overpasses and retaining structures were designed to accommodate floodplain constraints related to the Missouri River floodplain and to preserve right-of-way near heritage sites such as Forest Park and nearby cultural institutions like the Saint Louis Art Museum.

History

Planning for the spur emerged from mid-20th-century metropolitan freeway strategies influenced by interstate planning initiatives promulgated by the 1956 Act. Early proposals appeared in regional plans produced by entities including the Metropolitan St. Louis Sewer District planning records and consultations with the Missouri Department of Transportation. The alignment underwent multiple revisions following public hearings convened in municipal centers such as Clayton and University City, reflecting debates involving preservationists tied to Forest Park and business coalitions from Chesterfield and Brentwood.

Construction phases advanced during the 1960s and 1970s with contracts awarded to firms that had previously worked on projects for U.S. Route 66 realignments and expansions near Lambert–St. Louis International Airport. Environmental reviews in the 1980s prompted mitigating measures negotiated with advocacy groups including local chapters of The Nature Conservancy and historical societies preserving sites associated with Lewis and Clark Expedition commemoration areas. Subsequent rehabilitation projects in the 1990s and 2000s were coordinated with transit enhancements by Metro Transit and streetscape initiatives championed by municipal administrations such as St. Louis County, Missouri.

Exit list

Note: exit numbering and ramp configurations evolved through reconstruction programs managed by Missouri Department of Transportation. Key interchanges include: - Southern terminus interchange with I-64, providing connections toward St. Louis and Sullivan. - Mid-route junctions with Missouri Route 100 and Missouri Route 340 serving Maplewood and Clayton commercial districts. - Major connection to I-70 enabling movements toward Kansas City and Columbus. - Access points to municipal routes feeding University City and Richmond Heights civic centers. - Northern terminus ramps into central business districts adjacent to Clayton and proximate to county administrative complexes.

Auxiliary ramps provide direct access to logistics parks linked to BNSF Railway yards and to park-and-ride lots used by express buses to Downtown St. Louis and suburban employment nodes such as Chesterfield and Brentwood.

Future and planned developments

Long-range plans circulated by East-West Gateway Council of Governments and Missouri Department of Transportation include capacity enhancements, interchange modernization, and multimodal integration projects. Proposals reference congestion mitigation funded under program streams similar to those used for Surface Transportation Block Grant Program projects, aligning with regional initiatives to upgrade ramps, replace aging bridges near Missouri River approach spans, and add transit-priority lanes to support express bus operations managed by Metro Transit. Local jurisdictions including St. Louis County, Missouri and Clayton have considered context-sensitive redesigns to improve pedestrian connectivity to cultural assets like the Saint Louis Art Museum and to support redevelopment corridors linked to Washington University in St. Louis research campuses.

Planned environmental compliance work anticipates collaboration with conservation organizations and federal agencies such as the Environmental Protection Agency for stormwater management retrofits consistent with watershed works in the Missouri River basin.

Auxiliary and related routes

The spur interfaces with other auxiliary Interstate routes and state-designated connectors including corridors tied to I-270 and feeder routes paralleling U.S. Route 61 and U.S. Route 67. Local collectors and distributor roads developed in tandem with the spur include municipal arterials in University City, Clayton, and Richmond Heights that act as de facto auxiliary links for first- and last-mile access. Freight routing strategies coordinate with rail operators such as BNSF Railway and Union Pacific Railroad and with logistic centers serving companies headquartered in the region, while transit integration involves express services operated by Metro Transit and municipal shuttle programs in partnership with institutions like Washington University in St. Louis.

Category:Interstate Highways in Missouri