Between now and through summer of 2009, Techwood Drive, a north-south access road beside the Downtown Connector, is closed from 16th Street to 10th Street. With the closure, the southbound ramps from I-75 and I-85 to 14th and 10th streets also are shut off.

For drivers heading south from I-85, the beginning of the ramp will still be open to exit to 17th Street. From I-75, DOT says southbound drivers technically still can exit onto 16th Street, but the small streets could be such a mess they should forget about it, and exit at Northside Drive.

The 14th Street bridge itself will close altogether, but later this spring.

One of the goals of the finished project is to send exiting drivers directly to 10th Street, bypassing the 14th Street jam. It also adds a turn lane, a bicycle lane and wider sidewalks to the 14th Street bridge, and is designed to improve traffic flow from the connector and on the surface streets.

The true impact may emerge Monday morning, when southbound commuters to Georgia Tech and Midtown find two of their principal routes are off limits.

Officials are frantically exhorting drivers to get out of their cars — van pool, car pool, telework, walk, MARTA, anything. Or, failing that, to find an alternate route such as Northside Drive or Spring Street and avoid routes that lead through the twisty little streets around 16th Street.

"We've got to get 10 percent of the people out of their cars for [traffic] to be able to move," said Crystal Paulk-Buchanan, a DOT spokeswoman. "We really need 30 percent, but 10 percent is the absolute must-have."

Approximately 267,000 vehicles a day travel the connector. The work is part of the DOT's broader effort to accommodate the development boom in neighborhoods on both sides of the highway, like Atlantic Station.

The Clean Air Campaign, at www.clean aircampaign.com, helps solo drivers find commute alternatives.

While DOT gave drivers a taste of the coming affliction by narrowing Williams Street to one lane in October, the Techwood blockade marks the first complete closure of a road in the three-year project. The bridge closing this spring will be another.

And just to spice things up, in the midst of it all, the DOT is repaving the connector, starting this spring. Officials hope it can by done by closing lanes only at night.

Staff writer David Pendered contributed to this article.