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Construction of Thornton Interchange to begin Monday (March 21)

Construction of the Thornton Interchange (overpass) on U.S. Highway 20 north of Thornton will begin Monday (March 21). The project is scheduled for completion in October.

Nearly 20,000 vehicles per day travel through this area now.

During construction, traffic often will be reduced to one lane in each direction, and the speed limit will be reduced to 55 mph. Work will take place Monday through Saturday.

Here's a video of a drive-through of the new interchange concept.

Motorists should watch for construction workers and equipment and obey all traffic signs.

Crews have demolished existing homes and foundations at the site of the new interchange and are clearing vegetation, topsoil and debris as needed in preparation for road construction. Starting Monday, they will replace three irrigation lines under U.S. 20 and relocate power, phone, gas and cable lines around the site.

For safety purposes, crews will close 4985 South (Thornton intersection) on each side of U.S. 20 and 6800 South (River Bridge Road or Archer exit) just north of the Snake River as the project gets underway.

Workers also will close the median at 3800 South (Burton Road), eliminating left turns at this intersection. They will permanently close the local road in October.

4300 West (Bear World Drive) will remain open throughout the project and then permanently close in October. While open, motorists can turn left or right onto U.S. 20. Drivers can follow signs to businesses in Thornton using the south Rexburg interchange (Exit 332).

Eliminating perpendicular intersections and investing in interchanges for busy state highways improves road safety. These interchanges have fewer conflict points, because they separate turning movements from through traffic.

Western Construction Inc., of Boise, is the contractor for the $11.2 million construction project, which will elevate U.S. 20 to pass over 4700 South and will realign this county road north of its current location. Total cost of the new interchange, including land acquisition, design, construction and landscaping, will be nearly $20 million.

At the conclusion of the interchange project, all direct accesses to U.S. 20 between Lorenzo and Rexburg will be closed. In addition to 4985 South and 6800 South, these accesses include Bear World Drive, field turnoffs, and 3800 South. Motorists thereafter will access areas east and west of U.S. 20 via the new Thornton Interchange (Exit 328).

The new interchange will include north and south entrances and exits to improve entrance onto and exit from both U.S. 20 and 4700 South.