Highway work in downtown Chicago will be a two-tiered nightmare.(Chicago Tribune)

CHICAGO _ A great civic undertaking and a colossal traffic headache will unfold simultaneously in just a few weeks when the long-awaited demolition and reconstruction of historic Wacker Drive begins.

Drivers who have discovered the best shortcut through the famous Loop will have to bid farewell, at least temporarily, to the zigzagging express route the drive provides. And the thousands of bus riders will also be forced to alter their routines until about Thanksgiving 2002.

The massive $200 million project, paid for with a mix of federal and state funds, will affect more than 200,000 motorists a day over the next 20 months. The focus initially will be on the oldest and most deteriorated section of the unique double-decker roadway. That section was built 75 years ago as part of a plan to separate the fashionable upper boulevard from the vegetable and fish wholesalers who toiled in the cavern below.

"Wacker is a big, big project," Richard Kinczyk, first deputy commissioner in the Chicago Department of Transportation, said in an effort to brace commuters and downtown building owners for the rolling schedule of street closings and detours that will start at the end of February.

When work begins on the initial phase, Wacker's upper deck will be removed first, starting just east of State Street to Franklin Street. The supporting columns, rusted steelwork and other decaying infrastructure on Lower Wacker will then be knocked out and replaced using high-performance concrete that is less susceptible to cracking and water damage and expected to last between 75 and 100 years.

The span lengths between the support columns on Lower Wacker will be increased to up to 45 feet under the new design, reducing the number of columns needed and making it easier for drivers to safely maneuver along the subterranean freeway, which is officially designated as a federal highway.

"For $200 million, you do get rid of a few columns," said Stan Kaderbek, the city's chief ...