Missouri Route 141
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|Maintained by MoDOT|
|Length||30.902 mi (49.732 km)|
|South end||US 61 / US 67 in Arnold|
| I-55 in Arnold|
I-44 / US 50 in Fenton
I-64 / US 40 / US 61 in Town & Country
Route 364 in Maryland Heights
I-70 in Maryland Heights
|North end||Route 370 in Bridgeton|
|Counties||Jefferson, St. Louis|
Highway 141 is a highway located in the western St. Louis metropolitan area. Its northern terminus is at Route 370 in Bridgeton; its southern terminus is at U.S. Route 61/U.S. Route 67 in Arnold, in Jefferson County. The northern stretches of the highway are often referred to as the Maryland Heights Expressway or Earth City Expressway.
For the majority of its duration, Route 141 is a divided highway with four to eight lanes.
In Jefferson County, Route 141 is a four-lane highway. It has a southern terminus at U.S. Route 61/U.S. Route 67 in Arnold. At this point, it is an at-grade route with business driveways and traffic lights. It continues northwest and has an interchange with I-55. After the interchange, it becomes a rural highway with two lanes on each side with a wide median. The route has another interchange with the Route 21 freeway. It continues north and crosses the county line into Fenton in St. Louis County. 
St. Louis County
Route 141 enters St. Louis County in Fenton. It has an interchange with Route 30 and widens into a six to eight lane, partial access expressway. Heading north, there is a plaza to the left that includes various fast food restaurants, including St. Louis Bread Company, McDonald's, and Pizza Hut. After the plaza, Route 141 has at-grade interchanges with several collector roads.The highway heads northeast and has an interchange with Interstate 44 in Valley Park. The highway meets its northern terminus after the interchange with Route 370 at Missouri Bottom Road.
Old Highway 141 was a two-lane road built in the 1930s. The idea of an newer, divided highway carrying the Route 141 designation dates to the 1970s, when regional highway planners adopted the idea of an "outer belt" west of I-270. In 1976, Frank Kriz, then the district state highway engineer, called 141 an "old ridge-runner." The highways had traffic jams due to suburban growth. That same year, construction began for a new, four-lane Highway 141 in Jefferson County. Subsequent progress included a new bridge over the Meramec River at Valley Park in 1986 and a new interchange at Manchester Road in 1999. The section of Route 141 between Interstate 64 and the St. Louis County/Jefferson County line was upgraded to six lanes in a project completed in 2003.
In August, 2012, a six-lane realignment opened between Ladue Road and Page Avenue (Route 364), with interchanges at Ladue, Olive (Route 340), and Page. The section between Page and Olive (tentatively titled the Page-Olive Connector), which was constructed by St. Louis County has been turned over to the Missouri Department of Transportation and designated as Route 141. Maryland Heights Expressway (the section from Page north to I-70) and Earth City Expressway (the section from I-70 north to its terminus at Route 370) have also been designated as 141. As such, Route 141 now runs from US 61/67 in Arnold to Route 370 in Bridgeton.
The Missouri Department of Transportation (MoDOT) in cooperation with the St. Louis County Department of Highways and Traffic (DHT) expanded Route 141. 1 between just south of Ladue Road (Route AB) to Olive Road (Route 340). DHT extended Route 141 from Olive Road to the Page Avenue Extension (Route 364) at the Maryland Heights Expressway which links to the Earth City Expressway which continues north to Route 370 where it then turns into Missouri Bottom Road via Aubuchon Road. SPUIs were constructed at Ladue Road and Olive Blvd. There were some construction constraints with the part of the project between Olive and Page. DHT held studies of the environment to decide how to maneuver construction without disturbing some of the native wetlands in the corridor. During heavy rain, the current intersection at Creve Coeur Mill Road and Olive has the potential to flood, and most of the area along Creve Coeur Mill Road are either wetlands or farmland that lies in a flood plain.
St. Louis County Executive Charlie Dooley had called the project "one of St. Louis County's largest and most important infrastructure improvements this decade." The economic impact of the construction project was not nearly as massive as the upgrading and realignment project on Interstate 64/Highway 40. This construction project was estimated to have a $20 billion economic impact and create over 170,000 jobs during this current decade. 
|Jefferson||Arnold||0.000||0.000||US 61 / US 67 (Jeffco Boulevard)||Southern terminus at an at-grade intersection|
|0.379||0.610||I-55 – St. Louis, Cape Girardeau||Hybrid interchange (SPUI and diamond); exit 191 on I-55|
|3.585||5.769||Route 21 – St. Louis, Hillsboro||Diamond interchange|
|St. Louis||Fenton||7.583||12.204||Route 30 – St. Louis, St. Clair||Diamond interchange|
|11.127||17.907||I-44 / US 50 – St. Louis, Rolla||Exit 272 on I-44 / US 50|
|11.278||18.150||North Outer Road||Interchange|
|Twin Oaks||13.255||21.332||Big Bend Road||SPUI|
|Manchester||15.137||24.361||Route 100 / Lewis and Clark Trail (Manchester Road)||SPUI built in 1999|
|Town & Country||17.456||28.093||Clayton Road||Hybrid Trumpet Interchange|
|18.213||29.311||Salt Mill Road / South Outer Forty Drive||Interchange with traffic circles|
|18.665||30.038||I-64 / US 40 / US 61 – St. Louis, Wentzville||Exit 22 on I-64 / US 40 / US 61.|
|Chesterfield||19.974||32.145||Route AB (Ladue Road)||SPUI. Northern Extension begins|
|21.611||34.780||Route 340 (Olive Boulevard)||SPUI|
|Maryland Heights||23.563||37.921||Route 364 – St. Louis, St. Charles||Exit 17 on Route 364|
|27.983||45.034||I-70 – St. Louis, Kansas City||Cloverleaf interchange; exit 231 on I-70|
|Bridgeton||29.709||47.812||St. Charles Rock Road||At-grade-intersection|
|30.763||49.508||Route 370 – St. Louis, St. Charles||Northern terminus at a diamond interchange; exit 9 on Route 370|
|30.902||49.732||Missouri Bottom Road north||Continuation beyond northern terminus|
|1.000 mi = 1.609 km; 1.000 km = 0.621 mi|
- Missouri Department of Transportation (March 19, 2015). MoDOT HPMAPS (Map). Missouri Department of Transportation. Retrieved March 19, 2015.
- "Page to Olive Connector Study". St. Louis County Department of Highways and Traffic. Retrieved 2008-10-15.