Interstate 270 Missouri / Illinois


Interstates 270 and 255 comprise the outer belt freeway system of the St. Louis metropolitan area. Interstate 270 begins at the exchange with Interstates 55 and 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 through to Interstate 70 at Bridgeton.

The east-west portion 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. The rural style freeway continues east to Pontoon Beach and Glen Carbon, merging with I-70 at its split with 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 (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.

With Interstate 144 changed to 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 Interstate 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 (MO 340) and I-70, was dedicated on May 20, 1967.3

The same actions approved by 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 FHWA concurrence, on June 25 of that year.

The full cloverleaf interchange joining Interstates 255 and 70 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

Southern Terminus - Interstate 55 - Mehlville, Missouri
Perspective from Interstate 270 south
Two miles to the northwest of Interstates 55 (Exit 1A) and 255 on I-270 south at Sappington. Photo taken 12/20/09.
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. Photo taken 12/20/09.
An MODOT style end sign references the forthcoming transition of the St. Louis beltway from I-270 to Interstate 255 east. Photo taken 12/20/09.
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. Photo taken 12/20/09.
Exit 1A leaves the ending Interstate 270 through the cloverstack interchange with I-55. U.S. 61 & 67 parallel I-55 south along an arterial route to west Oakland and the city of Arnold. The two highways combine with U.S. 50 along Lindbergh Boulevard by adjacent South County Center mall to the north. Photo taken 12/20/09.
Replaced button copy guide signs at the loop ramp for Interstate 55 north. Now unnumbered, this ramp was formerly Exit 1B. Photo taken by Brian Dowd (06/02).
Perspective from Interstate 255 west
Interstate 255 splits with U.S. 50 (Lindbergh Boulevard) and passes below U.S. 61 (Lemay Ferry Road) on the half mile approach to Interstate 55 and the transition to I-270 north Photo taken by Brian Dowd (06/02).
One half mile east of Exit 1B for Interstate 55 north to Afton, Lemay and the Patch neighborhood of south St. Louis. Interstate 55 south connects I-255 and I-270 with Cape Girardeau in 103 miles and Memphis, Tennessee in 274 miles. Photo taken by Brian Dowd (06/02).
Interstate 255 west ends and Interstate 270 begins ends 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. Photos taken by Joel Wade (04/16/05).
Perspective from Interstate 55 north
Interstate 55 travels between the communities of Concord and Mehlville on the 1.5 mile approach to I-255 east and I-270 north (Exit 196). Photo taken 05/03/12.
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. Photo taken 05/03/12.
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. Photo taken 05/03/12.
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 nearby Lindbergh Boulevard (U.S. 50-61-67) commercial corridor. Photo taken 05/03/12.
Perspective from Interstate 55 south
Advance signage for Interstate 255 and 270 at Exit 199 on Interstate 55 south. Photo taken by Rich Piehl (12/00).
Interstate 55 southbound approaching the junction with Interstate 255/270 and U.S. 50/61/67. Photo taken by Rich Piehl (12/00)
Drivers bound for I-255 east to Columbia, Illinois and I-270 north back to Sunset Hills split. Photo taken by Brian Dowd (06/02).
Eastern Terminus - Interstates 55 and 70 - Troy, Illinois
Perspective from Interstate 270 east
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. A three-quarter cloverleaf joins I-270 with I-55 as Interstate 70 passes to the southeast between a pair of wye interchanges. Photo taken by Rich Piehl (04/01).
Perspective from Interstate 55 south
Interstate 55 heads south from eastern reaches of Edwardsville to meet both Interstates 70 east and 270 west at Exit 20. Photo taken by Brian Dowd (06/02).
One mile ahead of the three-quarter cloverleaf interchange (Exits 20B/A) with I-270 west to the Chain of Rocks Bridge and I-70 east to Effingham. Photo taken by Brian Dowd (06/02).
Long distance traffic to Kansas City is advised to take Interstate 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. Photo taken by Brian Dowd (06/02).
Guide signage on Interstate 55 south at Exits 20B/A for Interstate 270 west and Interstate 70 east. The next southbound exit for Illinois 162 is located one and a half miles to the south. Exit 18 is the first off-ramp for the Interstate 55 south/70 west overlap. The two Interstate will stay together for approximately 21 miles through until downtown Saint Louis. Photo taken by Brian Dowd (06/02).
Perspective from Interstates 55 north & 70 east
Interstate 55 northbound parts ways with Interstate 70 eastbound at Exit 20A. Exit 20B loops away from I-55 north to I-270 a short distance to the north. Photo taken by Rich Piehl (04/01).
Interstate 270 leads west from I-55 near Troy 15 miles to the Chain of Rocks Bridge to northern St. Louis. Photo taken by Rich Piehl (04/01).
Perspective from Interstate 70 west
Westbound Interstate 70 two miles from Interstates 55 and 270 west. Photo taken 10/16/04.
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. Photo taken 10/16/04.
Interstates 55 south & 70 combine through to I-64 in East St. Louis. I-270 bee lines west to I-70 at Bridgeton, Missouri. Photo taken by Jeff Morrison (08/13/05).
Westbound Interstate 70 splits to the left as the mainline transitions to Interstate 270. Exit 15B follows for Interstate 55 north to Springfield, Lincoln and Bloomington-Normal. Photo taken by Jeff Morrison (08/13/05).
Interstate 270 commences a rural drive 15 miles 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 taken by Jeff Morrison (08/13/05).


  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 July 23, 2017.

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