Counties Impacted
St. Louis


Project begins
Construction on the Route 141 Design Build project began in mid-2016.

Construction on the Route 141 Design Build project began in mid-2016.

ThrU Turns Open

ThrU Turns at Marshall Road and Vance Road opened in mid-2017. These signalized U-turns helped reduce the amount of backup on the road when left-turning traffic backed up into the through lanes of Route 141.

Northbound 141 to westbound I-44 loop ramp opens

A new loop ramp takes traffic from northbound 141 to westbound I-44 without needing to stop at a signal.

Eastbound I-44 flyover ramp opens

A new flyover ramp runs from the right lane of southbound 141 to the eastbound lanes of I-44 opens

Loop ramp westbound I-44 to southbound 141

Crews completed and opened a new loop ramp for westbound I-44 travelers to get onto  southbound 141 without stopping at a signal.

Triple left from eastbound I-44 to northbound 141.

Crews completed work to add a third left lane on the eastbound I-44 ramp to northbound 141.

Clean Up

Crews are currently in the process of final touches on the project -- cleaning up, patching roadways, and various other tasks before finishing the project.


What is the problem?

The interchange of I-44 and Route 141 is exceptionally crowded during morning and evening commutes.  With several major arterials, including Vance, leading to Route 141 near I-44, the roadway remains exceptionally congested.

What is currently underway

Crews have finished constructing most of the project and are currently working on wrapping up the project and completing final elements, including monitoring the flow of traffic through the project to ensure signals and traffic movements are timed optimally.

In late April, crews completed work on the new loop ramp between northbound 141 and westbound I-44. In May, they completed and opened the new flyover ramp from southbound 141 to eastbound I-44 and in late May, they completed the loop ramp from westbound I-44 to southbound Route 141 and added a third lane on the ramp from eastbound I-44 to northbound Route 141.

The ThrU Turns at Vance and Marshall opened in June 2017.

In February 2017, MoDOT relocated the Park and Ride lot from the west side of Route 141 to the east side.  Details on the relocation are here.


Project History

In January 2016, The Missouri Highways and Transportation Commission selected Pace Construction and its partners as the team with the project which provides the best apparent value for this project. 

One of the major goals of the project is to improve how efficiently traffic flows between I-44 and Route 141.  In addition, the department is looking to improve how efficiently traffic in the area moves through to Vance.

The project selected as the apparent best value constructs a flyover ramp from southbound Route 141 to eastbound I-44 and makes significant interchange improvements for northbound and southbound Route 141 to westbound I-44.  There will also be improved drainage to reduce flash flooding around the interchange.

In addition, the project will improve left turns to Marshall and Vance Road using signalized ThrU Turns. In a ThrU Turn, drivers pass the roadway and loop to an outside lane at the signal to make the turn onto the roadway.  This means less time waiting at a signal during peak traffic periods and improves the flow of traffic.  According to Federal Highway studies, this type on intersection reduces crashes by nearly 40 percent, making it much safer.

What are the construction impacts?

Construction impacts are projected to be fairly limited.  Most of the work on Route 141 will take place between 9 a.m. and 3 p.m. or between 6 p.m. and 5 a.m. The work on the north outer road portions of the project will experience the most impact to traffic, but this will not significantly impact traffic on Route 141 or I-44.  There are two closures on the outer road, each for three months, which will require a detour.

What are the goals for the project?

  • Deliver the project within the program budget of $25 million.
  • Maximize mobility on Route 141 and improve efficiency at the I-44 interchange and Vance Road intersection.
  • Deliver the project in a manner which demonstrates the importance of safety.
  • Provide a quality project resulting in a long-lasting transportation facility that minimizes future maintenance.
  • Deliver the project using a diverse workforce.
  • Complete the project by July 15, 2018.

Pace’s proposal included:

  • A flyover ramp from southbound Route 141 to eastbound I-44
  • Updated north outer road system with improved access between northbound and southbound Route 141 and westbound I-44
  • A relocated Park and Ride lot
  • Improved drainage to reduce the possibility of flash flooding
  • Signalized ThrU Turns at Vance and Marshall Roads to improve flow of traffic turning left

Most of the construction will take place during non-peak traffic hours, so it should not impact rush hours through the area significantly.  There are no long-term closures scheduled for either Route 141 or I-44.

What are ThrU Turns?

The basic concept of the ThrU Turn has been used for nearly 50 years. The ThrU Turn is used in urban areas, but is similar to Michigan lefts, downstream U-turns or J-turns.

In this case, the driver is prevented from making the direct turn and needs to follow the highway to a signalized median crossover. After making their U-turn, they can get into the right-most lane and make a turn. 

In the past, both northbound and southbound Route 141 backed up (northbound near Vance Road and southbound near Marshall Road) because of traffic turning left. Because the railroad bridge is very near to both Vance and Marshall, there is only so much space that the department could give to left turning traffic.

Traffic heading northbound, going to either Vance Road or Meramec Station Road, uses the ThrU Turn north of Vance Road.

Traffic heading southbound, going to Marshall Road or Forest Avenue, uses the ThrU Turn south of Marshall Road.

Please view the brochure to see more:

Making it ThrU a ThrU Turn


Driving through the new ThrU Turns
Is Responsive
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Community Involvement Group presentations

MoDOT has established a Community Involvement Group, where the department is reaching out to community leaders impacted by the project.  The intent of the group is to be one avenue of sharing information, and allowing these leaders to share the information with their constituents or employees.


The information to the right has been shared to the group.


Information on the contractor team.