Work is set to begin on a four-year, $475-million makeover of Chicago's Circle Interchange, the nation's worst bottleneck for trucks and one of the worst for automobiles.

The Illinois Department of Transportation says the revamped interchange, where the Eisenhower, Kennedy and Dan Ryan expressways converge west of Chicago's Loop, will reduce congestion by at least 50%. IDOT estimates the project will create 5,000 construction jobs.

Initial work will involve the Morgan Street Bridge and eventually encompass bridges, roadways and drainage systems for the expressways that make up the interchange, also known as the “spaghetti bowl” due to the curvilinear nature of its ramps.

The Federal Highway Administration and American Transportation Research Institute have identified the interchange, built between 1958 and 1962, as the No. 1 bottleneck among highways crucial to the nation's freight transportation system. A number of factors, including high traffic volumes, single-lane ramps and tight curves currently contribute to delays and congestion.

Accordingly, plans call for adding more lanes and reconfiguring ramps to promote safer and more efficient traffic flow. Once work is completed, portions of the interchange will provide as many as four lanes in both directions.

More than 400,000 vehicles use the interchange on a daily basis, about 33,000 of them trucks, according to IDOT. The interchange also is the site of more than 900 crashes per year.

IDOT consulted with a joint venture of engineer/architect AECOM and TranSystems Corp., both of Chicago, to develop concepts for the project. IDOT has programmed project costs into its 2014-2019 highway program.