Interstate 270 (Missouri–Illinois)

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Interstate 270

I-270 highlighted in red
Route information
Auxiliary route of I-70
Maintained by IDOT and MoDOT
Length50.59 mi[1] (81.42 km)
NHSEntire route
Major junctions
South end I-55 / I-255 in Mehlville, MO
Major intersections
East end I-55 / I-70 near Troy, IL
CountryUnited States
CountiesMO: St. Louis, City of St. Louis
IL: Madison
Highway system
IL 267IL I-280
Route 269MO Route 273

Interstate 270 (I-270) makes up a large portion of the outer belt freeway in Greater St. Louis. The counterclockwise terminus of I-270 is at the junction with I-55 and I-255 in Mehlville, MO; the clockwise terminus of the freeway is at the junction with I-55 and I-70 north of Troy, IL. The entire stretch of I-270 is 50.59 miles (81.42 km).

I-270 between I-70 and I-55 was formerly designated I-244, a western bypass of St. Louis, Missouri. It was originally proposed by Missouri as I-144, but the road was a beltway (or part of one), so the American Association of State Highway and Transportation Officials (AASHTO) assigned it the number I-244. By the late 1970s, the entire beltway (including today's I-255) was integrated as a part of I-270 for consistency. However, the politicians in Illinois started planning their supplemental freeway system in the mid-1970s, and a five-mile (8.0 km) section of Corridor 413 was included into the Interstate Highway System in April 1978.[2] This caused a potential place of confusion in Pontoon Beach, IL, where I-270 would have intersected itself, and eventually the IDOT (IDOT) decided on the I-255 numbering in 1980 (but not before considering renumbering an eight-mile (13 km) section to I-870).

Route description

In Missouri, I-270 diverges from at I-55 as a 10-lane freeway heading west of I-55's route but still maintaining a I-55's tendency to travel northward. I-270 intersects I-44 in a modified cloverleaf interchange that was rebuilt in the 1990s. Railroad overpasses and rocky bluffs between I-44 and Dougherty Ferry Road reduced the interstate to eight lanes for about two miles (3.2 km); however, this section was widened as of late 2013 to five lanes in each direction. I-270 meets up with I-64 with a stack interchange that was built from 1987 to 1993 (it was previously a cloverleaf that was a frequent source of backups).

Double white lines visible on northbound I-270 at I-70

From Dougherty Ferry Road through I-70, it continues as a 10-lane Interstate, although the right lanes often serve as exit lanes. The intersection with Route 340 (Olive Boulevard) was upgraded to a single-point urban interchange in the mid-2000s, and, during 2010–2011, the interchanges with Route 364 (Page Avenue) and Dorsett Road were upgraded with the latter becoming a diverging diamond interchange in October 2010.[3] Congestion in this area is severe to the point the MoDOT (MoDOT) has spent millions on various traffic control improvements since the 1990s. One of the safety improvements is a "double white line" that motorists are not permitted to cross (violation of that could lead to a fine of $500) that is located at the exits for I-70 in the northbound lanes. Other safety implementations include a special Maryland Heights police cruiser that is dedicated to traffic enforcement on this section of I-270, congestion warning signs, and traffic cameras.

At I-70, I-270 makes a transition from a north–south highway to an east–west highway though not signed as such until James S. McDonnell Boulevard and will eventually become a six-lane highway by the time it reaches U.S. Route 67 (US 67, North Lindbergh Boulevard). It then meets I-170, which had its interchange rebuilt from 2001 to 2004 during which a left exit lane in the westbound lane was corrected. This section of I-270 was a source of frequent backups during the late-afternoon hours until the interchange was rebuilt. A fatal accident in September 1999 spurred the rebuilding of the interchange, although the accident did not occur at that location happening a mile (1.6 km) east of the interchange. I-270 then passes various streets where every westbound exit connects to Dunn Road (and one must use Dunn Road to access I-270 with the only exceptions being the Route 367, Lilac Avenue, and Riverview Drive exits). Since Dunn Road handles two-way traffic, this has become a safety and congestion issue that MoDOT wants to address in the near future.

At Lilac Avenue, I-270 constricts to four lanes as it crosses the Mississippi River on the New Chain of Rocks Bridges. Leaving Missouri and entering Illinois, I-270 transitions from a suburban Interstate to an exurban Interstate with farm fields and wooded land bordering the Interstate in the area to the immediately east and west of the river crossing. Once it crosses the Chain of Rocks Canal, I-270 will intersect four different highways providing access to communities in eastern Madison: Illinois Route 3 (IL 3), Old Alton Road, IL 203, and IL 111. The interchange with IL 3 is a partial cloverleaf with the loop ramps in the northeast and southeast quadrants. The remaining two are cloverleaf interchanges, with the Old Alton Road/IL 203 interchange using a collector–distributor system with two folded diamonds due to the presence of railroad tracks between the two roadways. Once it passes IL 111, the speed limit increases to 65 mph (105 km/h) as the highway briefly becomes six lanes again with the junction with I-255. The highway then reverts to a four-lane highway offering diamond interchanges with IL 157 and IL 159 before meeting up with I-55/I-70 at the interchange that IDOT refers as the "3 I's". The eastbound I-270 meets the northeastbound combination of I-55 and I-70 which leave the intersection as northbound I-55 and eastbound I-70 which has adopted I-270's mile markings.


The section of I-270 on the Missouri side was completed by June 1964, while the section that was I-244 was completed by November 1968.[4] The section from Illinois Route 3 to I-55 in Illinois was finished by May 1965.[5]

During the Great Flood of 1993, the New Chain of Rocks Bridge carrying I-270 over the Mississippi River was the only bridge open from St. Louis to Keokuk, Iowa, at one point. (All other bridges from the McKinley Bridge to the Keokuk Bridge were closed at the peak of that flood.)

The last major construction project on I-270 occurred from 1995 to 1998. Both MoDOT and IDOT upgraded I-270 to modern standards from Lilac Avenue to I-255. However, this section of I-270 is still at two lanes in each direction.

On September 13, 1999, a fatal accident involving a tractor-trailer occurred in the westbound lanes of I-270[6] in front of the now-defunct St. Thomas Aquinas-Mercy High School (now North County Christian School) in northern St. Louis County. This accident sped up efforts that led to the I-170/I-270 interchange reconstruction that went from 2001 to 2004.

A major accident and fire from a FedEx Ground truck between the Route 367 and Lilac Avenue exits on October 28, 2002, forced detours and lengthy delays.[7][8]

There were plans to sign an eight-mile (13 km) section of I-270 from Glen Carbon to Edwardsville as I-870. However, this idea was discarded.

In 2008, MoDOT implemented new variable speed limits on I-270/I-255 with the normal limit being 60 mph (97 km/h).[9] However, due to complaints from the public, these signs were planned to be updated in 2011 to advisory signs.[10] A five-mile (8.0 km) section of I-270 between I-44 and Manchester was widened to five lanes in each direction, with work taking place between 2012 and 2013.[11] This section of I-270 sees up to 185,000 vehicles per day,[12] and peak hour congestion is common.


IDOT wanted to widen I-270 from Lilac Avenue to I-255 from four lanes to six, but no money was available at the time of the proposal in 2007.[13] However, IDOT has announced that nearly $100 million has been programmed for replacement of the canal bridges between 2011 and 2016.[14] The canal bridges were replaced in mid-2014, and the old deck was imploded late 2015.

MoDOT has also identified the need of improving the I-270 corridor in northern St. Louis County, which could cost in the range of $200 million.[15] The agency planned to widen the freeway from US 67 to Route 367 and rebuild every interchange (except I-170) and overpasses in this section. MoDOT held a public study of this corridor and has a website of this.[16] Construction eventually began in spring 2020 and is expected to conclude in December 2023 at a price of under $300 million.[17][18]

Exit list

MissouriSt. LouisMehlvilleConcord line0.000–
I-55 north – St. Louis
Counterclockwise terminus; exit 197 on I-55
US 61 / US 67 (Lemay Ferry Road)Southbound left exit only
I-55 south – Memphis
Southbound exit and northbound entrance; exit 196 on I-55

I-255 east – Chicago
Southbound left exit and northbound left entrance; clockwise terminus of I-255
ConcordSappington line2.1623.4792 Route 21 (Tesson Ferry Road)
Sunset Hills3.9036.2813 Route 30 (Gravois Road)
I-44 / US 50 / Route 366 east (Watson Road) – St. Louis, Tulsa
Signed as exits 5A (east) and 5B (west); exit 276 on I-44
Kirkwood7.88812.6957Big Bend RoadSouthbound exit and northbound entrance
Des Peres8.72914.0488Dougherty Ferry Road
9 Route 100 / Lewis and Clark Trail (Manchester Road)Also serves West County Center Drive
Town and Country12.386–
I-64 / US 40 / US 61 (Avenue of the Saints) – Wentzville, St. Louis
Exit 25 on I-64
Creve Coeur13.84722.28513 Route AB (Ladue Road)
14.99324.12914 Route 340 (Olive Boulevard)
Maryland Heights16.48626.53216
Route D east (Page Avenue)
Signed as exit 16A southbound; western terminus of Route D
Route 364 west – St. Charles
Signed as exits 16B southbound; eastern terminus of Route 364, exits 20A-B on route 364
17.94528.88017Dorsett Roaddiverging diamond interchange; orientation changes from north–south to east–west
20 I-70 – Kansas City, St. LouisSigned as exits 20A (east) and 20B (west); exits 232A-B on I-70; access to St. Louis Lambert International Airport
21.07433.915 Route 180 (St. Charles Rock Road) / Natural Bridge RoadSigned as exit 20C; access to SSM Health-DePaul
22B Route 370 – St. Charles CountySigned as exit 22 westbound; eastern terminus of Route 370
23.13737.23522AMissouri Bottom RoadEastbound exit and westbound entrance
Hazelwood23.83238.35423McDonnell Boulevard
25 US 67 (Lindbergh Boulevard)Signed as exits 25A (south) and 25B (north) westbound
I-170 south – Clayton, Lambert–St. Louis International Airport
Northern terminus of I-170; exits 10A-B on I-170; full Y interchange
26.88843.27226BNorth Hanley Road / Graham Road
Florissant27.86044.83627 Route N (New Florissant Road)
28.37545.66528Washington Street / Elizabeth Avenue
29.87548.07929West Florissant Avenue
30.58049.21430 Route AC (New Halls Ferry Road)
31.12050.08330AOld Halls Ferry RoadWestbound exit and eastbound entrance
Moline Acres31.10050.05131 Route 367 – St. Louis, Alton ILSigned as exits 31A (south) and 31B (north)
Bellefontaine Neighbors33.07753.23232Bellefontaine Road
34.06254.81733Lilac Avenue
City of St. Louis35.16756.59634Riverview Drive (Route H)
Mississippi River35.339
New Chain of Rocks Bridge
IllinoisMadisonChouteau Township2.734.393

IL 3 / Great River Road north / Great River Road Spur south – Granite City, Alton
Western end of concurrency with GRR;
signed as exits 3A (south) and 3B (north) eastbound
IL 203 south / Old Alton Road – Granite City
Two interchanges served by collector-distributor roads
IL 111 / Great River Road south – Pontoon Beach, Wood River
Eastern end of concurrency with GRR;
signed as exits 6A (south) and 6B (north)
I-255 south – Memphis

IL 255 north – Alton
Signed as exits 7A (south) and 7B (north) westbound;
exit 30 on I-255
Glen Carbon9 IL 157 – Collinsville, Edwardsville
11.8719.1012 IL 159 – Collinsville, Edwardsville
Pin Oak Township14.5723.4515A

I-55 south / I-70 west – City of St. Louis
Eastbound exit and westbound entrance; exit 20B on I-55
I-55 north – Chicago, Springfield
Exits 20A-B on I-55

I-70 east – Effingham, Indianapolis
Clockwise terminus
1.000 mi = 1.609 km; 1.000 km = 0.621 mi


  1. ^ DeSimone, Tony (October 31, 2002). "Table 2: Auxiliary Routes of the Dwight D. Eisenhower National System Of Interstate and Defense Highways as of October 31, 2002". Route Log and Finder List. Federal Highway Administration. Retrieved July 8, 2007.
  2. ^ FAI 270/FAP 413 Final Draft EIS Volume I (Report). 1983.[full citation needed]
  3. ^ "I-270 Dorsett/Page Project". MoDOT. October 17, 2010. Archived from the original on March 30, 2014. Retrieved January 20, 2012.
  4. ^ deLeon, Peter; Enns, John (September 1973). The Impact of Highways Upon Metropolitan Dispersion: St. Louis (PDF) (Report). Santa Monica, CA: The Rand Corporation. Retrieved January 2, 2012.
  5. ^ Sonderman, Joe. "May 17" (PDF). St. Louis History. Retrieved January 2, 2013.
  6. ^ Rackwitz, Jim (September 14, 1999). "Massive I-270 accident leaves tangled, burning wreckage". St. Louis Post-Dispatch. Archived from the original on January 6, 2009. Retrieved January 2, 2012.
  7. ^ . St. Louis, MO: KMOV-TV {{cite news}}: Missing or empty |title= (help)[dead link]
  8. ^ "FedEx truck crashes, burns on 270". Alton Telegraph. October 30, 2002. p. A1.
  9. ^ "Variable speed limit begins today on I-270". St. Louis Post-Dispatch. Archived from the original on June 25, 2008.
  10. ^ Leiser, Ken (March 9, 2011). "I-270, I-255 speed signs will be 'advisory'". St. Louis Post-Dispatch. Retrieved January 2, 2012.
  11. ^ Leiser, Ken (February 28, 2011). "MoDOT plans to widen stretch of I-270". St. Louis Post-Dispatch. Retrieved January 2, 2013.
  12. ^ District 6 Traffic Volume and Commercial Vehicle Count Map (PDF) (Map). Cartography by Transportation Planning. Missouri Department of Transportation. 2010. Archived from the original (PDF) on January 7, 2012. Retrieved January 2, 2012.]
  13. ^ "Transportation Infrastructure Proposals". Southern Illinois University. Archived from the original on March 13, 2007. Retrieved January 2, 2013.
  14. ^ District 8 Staff. "FY 2011–2016 Highway Improvement Program, District 8" (PDF). Illinois Department of Transportation. Retrieved January 2, 2013.{{cite web}}: CS1 maint: numeric names: authors list (link)
  15. ^ Keith, Kevin. "I-270 Improvements from McDonnell Blvd. to the Chain of Rocks Bridge" (PDF). The Case for Capacity. American Association of State Highway and Transportation Officials. Archived from the original (PDF) on March 17, 2012. Retrieved January 2, 2013.
  16. ^ "I-270 North Project". Retrieved November 19, 2022.
  17. ^ "I-270 North Project". Retrieved November 19, 2022.
  18. ^ Payoute, Jasmine (March 5, 2020). "Major I-270 construction to begin soon | Here's what drivers need to know". Retrieved November 19, 2022.
  19. ^ Missouri Department of Transportation (March 19, 2015). MoDOT HPMAPS (Map). Missouri Department of Transportation. Retrieved March 19, 2015.
  20. ^ Street Atlas USA (Map). DeLorme. 2007.

External links