Interstate 255

Interstate 255 (I-255) is a bypass route of I-55 in Greater St. Louis. Along with I-270, it forms a loop around the central portion of the bi-state metro area; a majority of I-255 is located on the Illinois half. It shares its southern terminus with I-270 at the junction with I-55; I-270 goes to the west, and I-255 goes to the east. U.S. Route 50 (US 50) joins I-255 at Lemay Ferry Road. It crosses the Mississippi River on the Jefferson Barracks Bridge, enters Illinois, and then turns northeast. There is a junction with I-64, where US 50 breaks off and goes east, and then further north there is a junction with I-55 again, I-70, and US 40, all of which are all co-signed together. The next junction is another one with I-270, which is the northern terminus of I-255. After that, the limited-access freeway continues on as Illinois Route 255 (IL 255). I-255 is 30.82 miles (49.60 km) in length.

Interstate 255
I-255 highlighted in red
Route information
Auxiliary route of I-55
Maintained by IDOT and MoDOT
Length30.82 mi[1] (49.60 km)
Historycompleted in 1986
Major junctions
West end I-55 / I-270 in Mehlville, MO
North end I-270 / IL 255 in Pontoon Beach, IL
CountiesMO: St. Louis
IL: Monroe, St. Clair, Madison
Highway system
Route 254MORoute 265
IL 251ILIL 255

Route description

I-255's counterclockwise terminus is at an interchange with I-55 and I-270 in Mehlville, Missouri. The beltway is designated as I-270 (with Kansas City as the control city) west of this interchange and as I-255 east (with Chicago as the control city) east of this interchange. The section of I-255 east from this interchange to the Jefferson Barracks Bridge was first built in the 1960s to carry U.S. Route 50 traffic across the Mississippi River. The roadway was upgraded between 2002 and 2004. Repairs included both new pavement and the replacement of the Telegraph Road bridge.

Once it crosses the Mississippi River and enters Illinois, I-255 is signed as a north/south highway. It is considerably newer than the Missouri section, having been constructed in the 1980s. At the Illinois Route 3 interchange, I-255 turns sharply to the north. It is briefly duplexed with Illinois 3 in Dupo. After Dupo, I-255 turns northeast, skirting Cahokia and East St. Louis. An interchange at Mousette Lane in Sauget was constructed in the 1990s and provides motorist access to GCS Ballpark (home to the Gateway Grizzlies baseball team) and the St. Louis Downtown Airport. Given its proximity to the airport, this section of I-255 features shorter light poles to better accommodate takeoffs and landings.

North of Sauget, I-255 traverses a portion of the Frank Holten State Recreation Area before an interchange with Interstate 64 west of Caseyville. This section of freeway opened in 1986.[2] Traffic can enter and exit I-255 at an interchange with Collinsville Road (formerly U.S. Route 40) just east of the Fairmont Park Racetrack.

I-255 meets I-55/I-70 at an interchange in Collinsville, its original intended terminus. North of this interchange, the control city for I-255 changes from "Chicago" to "To I-270". In the 1980s, I-255 was extended approximately five miles north to meet I-270 in Pontoon Beach, its current terminus. While the I-255 designation ends at the I-270 interchange, the freeway continues north and west (parallelling the bend in the Mississippi River) for approximately 23 miles as Illinois Route 255. The decision to not extend the I-255 designation to the new freeway reflects the fact that state and not federal funds were used to pay for construction.


I-255 route was proposed from I-55/I-244 near Green Park to I-55/70 west of Cahokia Mounds[3] near the intersection with IL 111 when plans surfaced in the 1950s Yellow Book. It was originally designed to be a four lane highway but was changed to six lanes.[4]

Since that routing was to go through the American Bottoms, archaeological investigations had to be conducted prior to any construction, which would later become known as the FAI 270 Series. When Cahokia Mounds was designated in the federal register, an alternative alignment for I-255 from I-64 to I-55/70 was selected.[5] This delayed construction of I-255 until the late 1970s, making it the last interstate highway in metropolitan St. Louis to be built.

Both the western (I-270) and eastern (I-255) portions of the interstate loop around St. Louis were originally designated as I-270. However, the route that Illinois selected ("Corridor 413"[6]) included an interchange in Pontoon Beach between the new beltway (running north and south parallel to the Mississippi River) and the existing beltway (running east and west to a terminus at I-55/I-70). As such, two intersecting interstate highways would have carried the same route number.[7] As such, Illinois' Department of Transportation (IDOT) concluded a different route number would be necessary for the eastern leg of the beltway. While I-870 was initially considered,[8] informal use of I-255 in contemporary local media coverage led to its widespread adoption. By 1980, IDOT announced that the eastern portion of the St. Louis beltway was to be designated as I-255.

Exit list

MissouriSt. LouisConcord0.000.00 I-270 north Kansas CityClockwise terminus; continuation beyond I-55
ConcordMehlville line1 I-55 St. Louis, MemphisI-55 exit 196; signed as exits 1A (south) & 1B (north); westbound exits and eastbound entrances
Mehlville0.50.801B US 61 / US 67 (Lemay Ferry Road)Eastbound exit and westbound entrance
1.21.91C US 50 west (Lindbergh Boulevard) to US 61 / US 67 (Lemay Ferry Road)West end of US 50 overlap; westbound exit and eastbound entrance
2.23.52 Route 231 (Telegraph Road)
3.25.13Koch RoadOrientation changes from east-west to north-south
Mississippi River3.5–
Jefferson Barracks Bridge
6 IL 3 south / Great River Road south ColumbiaSouth end of IL 3 / GRR overlap
St. ClairDupo9.214.89S. Main Street/Old Route 3 Dupo
10.617.110 IL 3 north / Great River Road north Cahokia, East St. LouisNorth end of IL 3 / GRR overlap
Cahokia13.020.913 IL 157 (Camp Jackson Road) Cahokia
Centreville15.024.115Mousette Lane
Alorton16.726.917 IL 15 (New Missouri Avenue) Belleville, East St. LouisSigned as exits 17A (east) and 17B (west)
East St. Louis18.629.919State Street East St. Louis
Caseyville20.132.320 I-64 / US 50 east St. Louis, LouisvilleI-64 exit 7; north end of US 50 overlap
St. ClairMadison
county line
Collinsville23.638.024Collinsville Road
Madison24.839.925 I-55 / I-70 (US 40) Chicago, Indianapolis, St. LouisI-55/I-70 exit 10; signed as exits 25A (north/east) & 25B (south/west)
Pontoon Beach26.041.826Horseshoe Lake Road
29.247.029 IL 162 Granite City, Glen Carbon
30.8249.6030 I-270 Indianapolis, Kansas CityI-270 exit 7A westbound, 7 eastbound; counterclockwise terminus
IL 255 north (Alton Bypass) AltonContinuation north beyond I-270
1.000 mi = 1.609 km; 1.000 km = 0.621 mi


KML is from Wikidata
  1. "Route Log and Finder List - Interstate System - table 2". Federal Highway Administration. 2002-10-31. Retrieved 2007-07-08.
  2. Alton Telegraph, October 24, 1986
  3. 1970 USGS Topo Map
  4. Alton Telegraph, April 29, 1977
  5. Edwardsville Intelligencer, July 9, 1973
  6. Illinois Supplemental Freeway
  7. IDOT FAI-270/FAP 413 Draft EIS Volume 1, 1983
  8. I-270/870 proposed routes
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