Interstate 255 (I‑255)

Interstate 255 (I‑255)
State	MO/IL
Route	255
Length mi	30.90
Established	1980s
Terminus a	near Mehlville, Missouri
Terminus b	near Columbia, Illinois
Counties	St. Louis County, St. Louis, Madison County, St. Clair County, Illinois

Contents

Interstate 255 (I‑255) is an auxiliary Interstate bypass of Interstate 55, Interstate 64, and Interstate 70 that serves the Greater St. Louis metropolitan area. The route links suburbs and satellite cities on the eastern and southern periphery of St. Louis, traversing both Missouri and Illinois and crossing the Mississippi River via the Jefferson Barracks Bridge. It functions as part of the regional network connecting to I‑270, I‑70, US 50, and Illinois Route 3.

Route description

I‑255 begins at a trumpet interchange with I‑270 and U.S. Route 61 near Mehlville, Missouri and curves southeastward past Jefferson Barracks National Cemetery, Jefferson Barracks Park, and the Missouri River floodplain. The freeway parallels US 50 and intersects arterial routes that serve Arnold, Missouri, Granite City, Illinois, and Fairview Heights, Illinois. After crossing the Mississippi River on the Jefferson Barracks Bridge, the alignment traverses Madison County, Illinois and St. Clair County, Illinois with interchanges providing access to Illinois Route 111, Illinois Route 3, and Illinois Route 15. Near its northeastern terminus the highway connects to I‑70 and rejoins I‑55, completing the partial beltway around St. Louis County, Missouri and linking to through routes toward Chicago, Springfield, Illinois, and Indianapolis.

Planning for an outer loop around St. Louis that included the I‑255 corridor emerged from postwar metropolitan studies influenced by proposals from Federal-Aid Highway Act of 1956 planners and regional engineers from Metropolitan St. Louis Sewer District reports of the 1960s and 1970s. The corridor incorporated and paralleled existing alignments such as US 50 and sections of Illinois Route 3. Construction phases unfolded in the late 1970s and 1980s, with major structures including the Jefferson Barracks Bridge—a replacement and expansion project coordinated with the United States Army Corps of Engineers and state transportation departments: Missouri Department of Transportation and Illinois Department of Transportation. Environmental reviews referenced precedents like the National Environmental Policy Act of 1969; mitigation included wetlands work and coordination with Fish and Wildlife Service programs. Subsequent interchange upgrades paralleled interstate developments such as expansions on I‑70 and projects coordinated under the Federal Highway Administration and regional planning bodies like the East-West Gateway Council of Governments.

The I‑255 exit sequence integrates connections to primary routes and local thoroughfares serving South County, St. Louis County, Missouri and Illinois suburbs. Major junctions include the western terminus at I‑270 and US 61, interchanges with US 50, Route 141, the Jefferson Barracks Bridge crossing of the Mississippi River, and Illinois interchanges with Illinois Route 3, Illinois Route 111, Illinois Route 159, and the northeastern terminus where I‑255 meets I‑55/I‑70. Collector–distributor ramps and directional flyovers provide movements toward Memphis, St. Louis Lambert Airport, Cape Girardeau, and links toward I‑64 and I‑270 (IL). Service areas and park-and-ride facilities are located near interchanges that serve Granite City, Collinsville, Illinois, and Fairview Heights.

Planned improvements have focused on interchange modernization, pavement rehabilitation, and bridge maintenance coordinated by Missouri Department of Transportation and Illinois Department of Transportation with funding mechanisms tied to federal programs administered by the Federal Highway Administration and state legislatures such as the Illinois General Assembly and Missouri General Assembly. Projects under study include widening segments near growth corridors servicing Scott Air Force Base, capacity increases to meet projections from the U.S. Census Bureau on metropolitan growth, and resiliency upgrades addressing flooding associated with the Mississippi River and climate projections discussed in National Climate Assessment reports. Corridor studies have involved stakeholder input from municipalities including Belleville, Illinois, O'Fallon, Illinois, and regional transit agencies such as the Bi-State Development Agency.

I‑255 functions as one arm of the outer belt around St. Louis complementary to I‑270; it interfaces with U.S. highways such as US 50, US 61, and state highways including Illinois Route 3, Illinois Route 111, and Route 141. The corridor’s planning and interchange design referenced national standards from the American Association of State Highway and Transportation Officials and has been coordinated through the East-West Gateway Council of Governments regional plans. Related infrastructure projects have involved river crossings like the McKinley Bridge, rail-grade separation projects with Union Pacific Railroad and Norfolk Southern Railway, and transit coordination with agencies such as MetroLink.