Interstate 270 Missouri / Illinois

Interstate 270 Missouri
Interstate 270 Illinois


I-270 and I-255 comprise the outer belt freeway system of the St. Louis metropolitan area. Interstate 270 begins at the exchange with I-55/255 south of St. Louis near Mehlville. Northward from there, the freeway loops through Sunset Hills, Kirkwood and Creve Coeur among other St. Louis County suburbs to Interstate 70 at Bridgeton.

The northern leg of I-270 extends from Bridgeton through Hazelwood, Florissant and Bellefontaine Neighbors to the Chain of Rocks Bridge over the Mississippi River. Crossing into Madison County, Illinois, I-270 navigates along a causeway on Chouteau Island to Chain of Rocks Canal and northern reaches of Granite City. With a rural design, I-270 continues east to Pontoon Beach and Glen Carbon, converging with I-70 at I-55 near Troy.

Mile posts along Interstate 270 increase from zero at I-55 and I-255 in south St. Louis County to 34 at the Mississippi River. Illinois restarts the count at zero at the Missouri state line and continues to 15 at I-55/70. Despite Interstate 70 meeting the east end of I-270 at around milepost 19, the numbering sequence from I-270 extends east along I-70.


The Urban Route Numbering proposals submitted to the American Association of State Highway Officials (AASHO) on July 31, 1958 outlined three numbers for the St. Louis beltway system:

  • Interstate 144 for the Southwest Beltway, from I-55 north to I-70.
  • Interstate 255 for the Easterly route to the Illinois state line at the Mississippi River.
  • Interstate 270 for the North Beltway from I-70 east to the Chain of Rocks Bridge.
St. Louis Urban Area Interstates - 1958

Route Information

  • East End – Troy, IL

  • South End – Mehlville, MO

  • Total Mileage – 50.59

Missouri – 35.62

  • Cities – St. Louis, Florissant, Ferguson, Bridgeton, Kirkwood

  • JunctionsI-55 I-44 I-64 I-70 I-170

Illinois – 14.97

  • Cities – East St. Louis, Granite City

  • JunctionsI-255 I-55 I-70

Source: December 31, 2021 Interstate Route Log and Finders List

St. Louis, MO - 1977

1977 Illinois Official Highway Map showing the small portion of I-255 opened at the time designated as part of an extended Interstate 270.

With Interstate 144 changed to I-244 since it formed part of a loop, AASHO approved the Interstate Route Numbering for Missouri on November 10, 1958.1

Named the Circumferential Expressway, the quadrant of I-270 between I-55 at Mehlville and I-70 at Champ remained signed as Interstate 244 until 1974. The route was renumbered as an extended I-270 to alleviate motorist confusion.2 The final segment for I-244, Olive Boulevard (Route 340) and I-70, was dedicated on May 20, 1967.3

The same actions approved by the American Association of State Highway and Transportation Officials (AASHTO) on June 25, 1974 to renumber I-244 included the renumbering of I-255 to I-270 as well. The southeast loop changed back to Interstate 255 in 1979. AASHTO approved the redesignation, subject to concurrence from the Federal Highway Administration (FHWA concurrence), on June 25 of that year.

The cloverleaf interchange joining I-255 and I-270 with I-55 at Mehlville was upgraded to a cloverstack interchange from 1991 to 1994. Road construction included building collector distributor roadways along both sides of I-55 north to Lindbergh Boulevard (U.S. 50/67), where a diamond interchange was upgraded to a SPUI. The project addressed a weaving traffic pattern. Work continued through 1997 along I-270, with the beltway expanded northward from I-55 to I-44 to eight overall lanes.3

East End I-55 I-70 – Troy, Illinois

I-270 East at I-55 I-70

I-270 east at I-55/70 - Glen Carbon, IL

Eastbound I-270 at IL 159 to Edwardsville. The freeway proceeds 2.5 miles to Exit 15 with I-55/70 south and I-55 north. 05/24/18

I-270 east at I-55/70 - Glen Carbon, IL

Spanning Old Troy Road, one mile ahead of Exit 15A for I-55 south / I-70 west to Troy and Collinsville. 05/24/18

I-270 east at I-55/70 - Troy, IL

I-70 is omitted from signs for Exit 15A along Interstate 270 east to offset potential confusion for travelers headed east along the freeway to Indianapolis. 05/03/12

I-270 east at I-55/70 - Troy, IL

A three quarter cloverleaf joins I-270 with I-55 as Interstate 70 passes to the southeast between a pair of wye interchanges. 05/24/18

I-270 east at I-55/70 - Troy, IL

Interstate 55 continues north from I-70/270 along a rural freeway to Springfield. 05/03/12

I-270 east at I-55/70 - Troy, IL

Exit 15B loops onto I-55 north from the ending I-270 east. Interstate 55 concludes in 275 miles at U.S. 41 (Lake Shore Drive) in Chicago. 05/03/12

I-70 West at I-55 I-270

I-70 west at I-55/270 - Troy, IL

Westbound Interstate 70 two miles from I-55 and I-270 west. Photo by Eric Stuve (07/22/16).

I-70 west at I-55/270 - 2004

The initial guide sign for I-270 and Exit 15B for I-55 north was replaced by 2016. 10/16/04

I-70 west at I-55/270 - Troy, IL

One mile ahead of the I-70 westbound split with Interstate 270. The wye interchange is unnumbered, with Exit 15B designated for the adjacent ramp to Interstate 55 north. 10/16/04

I-70 west at I-55/270 - Troy, IL

I-55/70 combine southwest to I-64 in East St. Louis. I-270 bee lines west to I-70 at Bridgeton, Missouri 10/16/04

I-70 west at I-55/270 - Troy, IL

Westbound I-70 splits to the left as the mainline transitions to Interstate 270. Exit 15B follows for I-55 north to Springfield, Lincoln and Bloomington-Normal. 10/16/04

I-70 west at I-55/270 - Troy, IL

Interstate 270 commences a rural route 14.97 miles west to the Missouri state line on the Chain of Rocks Bridge as I-70 angles southwest with I-55 to Troy, Collinsville and East St. Louis. Photo by Jeff Morrison (08/13/05).

I-55 South at I-70 I-270

I-55 south two miles from I-70/270 at Edwardsville, Illinois

Interstate 55 heads south from eastern reaches of Edwardsville to meet both I-70 east and I-270 west at Exit 20. 12/31/23

I-55 south meets I-270 in one mile near Troy, Illinois

One mile ahead of the three quarter cloverleaf interchange (Exits 20 B/A) with I-270 west to the Chain of Rocks Bridge and I-70 east to Effingham. 12/31/23

Maple Grove Rd spans I-55 south ahead of Exit 20 B for I-270 west

Long distance travelers headed to Kansas City are advised to take I-270 west across the north side of the St. Louis suburbs in lieu of I-70 west. I-70 angles southwest with I-55 to East St. Louis and across the Stan Musial Veterans Memorial Bridge into St. Louis. 12/31/23

I-55 south at I-270 west to Glen Carbon, Pontoon Beach and Florissant, MO

Exit 20 B leaves I-55 south for I-270 west to Granite City, north St. Louis and Florissant, Missouri. Interstate 55 advances south to combine with I-70 west for a 15.5 mile overlap to East St. Louis. 12/31/23

I-55 North I-70 East at I-270

I-55/70 north at I-270 - Troy, IL

Interstate 55 northbound parts ways with I-70 eastbound at Exit 20A. Exit 20B loops away from I-55 north to I-270 a short distance to the north. 05/07/18

I-55 north at I-270 - Troy, IL

Interstate 270 leads west from I-55 near Troy 15 miles to the Chain of Rocks Bridge to northern St. Louis. 05/24/18

I-270 East End Throwback

I-55 South at I-70 I-270

I-55 south at I-70/270 - 2002

Two miles north of I-70 and I-270 west on I-55 south at the Goshen Road overpass. Photo by Brian Dowd (06/02).

I-55 south at I-70/270 - 2002

All guide signs for the upcoming exchange with I-70/270 were replaced to use Clearview font. Photo by Brian Dowd (06/02).

I-55 south at I-70/270 - 2002

I-55 south at I-270 west. I-55 combines with I-70 west just ahead of IL 162 to Troy. Photo by Brian Dowd (06/02).

I-55 south at I-270 west and I-70 in 2018

Overheads using Clearview font at Exit 20 B were replaced in kind using Highway Gothic font. 05/06/18

South End I-55 – Mehlville, Missouri

I-270 South at I-55 I-255

I-270 south at I-55/255 - Concord, MO

Two miles to the northwest of Exit 1A for I-55 and I-255 east on I-270 south at Sappington. 12/20/09

I-270 south at I-55/255 - Concord, MO

Two lanes drop from Interstate 270 east for the collector distributor roadway to I-55 south to Memphis, Tennessee, I-55 north to St. Louis and U.S. 61/67 (Lemay Ferry Road) at Forder Road. 12/20/09

I-270 south at I-55/255 - Concord, MO

An MODOT style end sign references the forthcoming transition of the St. Louis beltway from I-270 to Interstate 255 east. 12/20/09

I-270 south at I-55/255 - Concord, MO

Theiss Road spans Interstate 270 a quarter mile from the partition with the three lane c/d roadway for Interstate 55 south to Festus and Cape Girardeau and north to Lemay and Downtown St. Louis. 12/20/09

I-270 south at I-55/255 - Concord, MO

Exit 1A leaves the ending Interstate 270 through the cloverstack interchange with I-55. 12/20/09

I-270 south at I-55/255 - Concord, MO

U.S. 61/67 parallel I-55 south along an arterial route to west Oakland and the city of Arnold. U.S. 61/67 combine with U.S. 50 along Lindbergh Boulevard by adjacent South County Center mall to the north. 12/20/09

I-255 West at I-55 I-270

1.75 miles ahead of I-55/270 on I-255 west in Mehlville, Missouri

West from Route 231, Interstate 255 separates with U.S. 50 (Lindbergh Boulevard) ahead of U.S. 61/67 (Lemay Ferry Road) on the 1.75 miles leading to the exchange with I-55 and transition to I-270 north. 12/31/23

I-255 west at I-55/270 - Mehlville, MO

Exit 1B connects I-255 west with Interstate 55 north to Afton, Lemay and the Patch neighborhood of south St. Louis. Interstate 55 south travels 103 miles to Cape Girardeau and 274 miles to Memphis, Tennessee. Photo by Eric Stuve (08/18/18).

I-255 west at I-55/270 - Mehlville, MO

Interstate 255 west becomes I-270 north above the center line of I-55. Leading north from I-255 at Exit 1B, Interstate 55 travels 11.2 miles to combine with I-44 east between the La Salle Park and Soulard neighborhoods in St. Louis. Photo by Eric Stuve (08/18/18).

I-55 North at I-255 I-270

I-55 north at I-255/270 - Mehlville, MO

Interstate 55 travels between the communities of Concord and Mehlville north 15 miles to I-255 east and I-270 north at Exit 196. 05/03/12

I-55 north at I-255/270 - Mehlville, MO

A two lane flyover (Exit 196) departs I-55 north in three quarters of a mile for I-270 north and I-255 east. The west beltway connects I-55 with I-44 at Sunset Hills, I-64 at Town and Country and I-70 at Bridgeton. 05/03/12

I-55 north at I-255/270 - Mehlville, MO

Exit 196 carries all traffic in unison to Interstate 255 east for Chicago and Indianapolis, Indiana and I-270 north for Columbia and Kansas City. 05/03/12

I-55 north at I-255/270 - Mehlville, MO

Upgrades made at Exit 196 in 1991-94 replaced a loop ramp from I-55 north to I-270 north with a two lane flyover. A c/d roadway emerges from the I-55 mainline north next to the commercial corridor along nearby Lindbergh Boulevard (U.S. 50-61-67). 05/03/12

I-55 South at I-255 I-270

Exit 199 departs I-55 south two miles ahead of I-255/270 at Affton, MO

I-55 heads two miles south from Exit 199 to Reavis Barracks Road at Afton to the c/d roadway system (Exit 197) for U.S. 50-61-67 (Lindbergh Boulevard) at I-255/270. 12/31/23

I-55 advances south between Green Park and Mehlville, MO to I-255/270

Interstate 55 runs between the city of Green Park and unincorporated Mehlville to the separation with the c/d roadway for I-255 east to Chicago, Illinois and I-270 north to Kansas City. 12/31/23

The distributor roadway at Exit 197 separates from I-55 for U.S. 50/61/67 and I-255/270

Three lanes partition from I-55 south for I-255/270 ahead of the single point interchange (Exit 197) for U.S. 50-61-67 (Lindbergh Boulevard). 12/31/23

Exit 197 partitions next for I-270 west to Sunset Hills, MO and I-255 east to Columbia, IL.

Traffic splits on the c/d roadway at Exit 197 for I-255 east to Columbia, Illinois and I-270 west back to Kirkwood. 12/31/23

Exit 197 south at the beginning of I-255 east and I-270 west

The flyover for I-255 east joins the freeway just ahead of U.S. 61/67 (Lemay Ferry Road) in Mehlville. I-270 heads 5.8 miles northwest from I-55 to a cloverstack interchange with I-44 in Sunset Hills. 12/31/23


  1. MISO (Missouri Interstate Route Numbering), Interstate system route numbering web site, Stephen Summers.
  2. “I-255 Rim Means Loop is Finished – For Now.” St. Louis Post-Dispatch (MO), July 31, 1988.
  3. I-244 and I-270 1964-1968 [Facebook update]. Retrieved from
  4. “Interchange Reconstruction Gets Off To Early Start.” St. Louis Post-Dispatch (MO), December 16, 1991.

Page updated January 28, 2024.