Starting tonight, hundreds of thousands of motorists will be squeezed for six months while Interstate 35W south of downtown Minneapolis gets an overhaul. But traffic engineers say the reward will be a 21st-century freeway.

The disruption starts at 9 p.m. and runs through September as northbound and southbound 35W shrink from four lanes to three between 42nd Street and just south of downtown. It's just the beginning of pain that will spread as far as Burnsville.

When the work is complete, drivers will use a highway unlike any other in the United States, said Nick Thompson, the Minnesota Department of Transportation engineer in charge of the project.

Electronic signs will be placed above each lane every half-mile, allowing traffic engineers to instantly illuminate a red X if a stalled vehicle is in a certain lane or post an "advisory speed limit" to warn drivers of slower traffic ahead. The four northbound lanes will be joined by a fifth shoulder lane that will be open to buses, carpoolers and solo drivers who have signed up for the MnPass electronic tolling system.

Congestion reduction is the goal of the project, which is being paid for with money from a $133 million federal grant and $50 million in state matching funds. The Twin Cities region was one of several metro areas around the country chosen to try new ways of keeping traffic moving.

No official detours are being announced, but drivers will need to pay attention all summer because there will be as many as eight different weekend closures of the freeway, Thompson said. There will also be middle-of-the-night spot closures of about 15-20 minutes while signs are erected.

Because the southbound squeeze will take two lanes from 35W and two lanes from downtown and merge them into three lanes total, Thompson said backups could spread to the I-94/35W commons section.

As summer arrives, many ramps in the corridor will be closed for one to two weeks, he said, while others will be closed the whole season -- and this comes on top of the massive, messy Crosstown Commons reconstruction, which will continue until 2010.

The inconvenience will extend all the way to Dakota County, as lanes on 35W are closed south of I-494. When that work is done, the carpool lanes in that area will be converted to MnPass lanes such as the ones on I-394, and there will be a new southbound lane for general traffic over the Minnesota River.

Buses won't glide by, either

While commuters who take transit will avoid gnashing their teeth behind the wheel, the advantages that buses enjoy -- namely bus-only shoulder lanes -- will largely disappear in south Minneapolis during the construction period. They'll be sharing the narrower road with everyone else. More than 200,000 vehicles a day use 35W at Lake Street.

The good news is that when the work is done, buses that are now limited to 35 miles per hour on the shoulders should be able to go full freeway speed in the new MnPass shoulder lane. As on 394, the toll for solo drivers will be raised as needed to keep the lane free-flowing.

To make up for the narrower shoulders after the freeway upgrade is finished, the state is installing emergency pull-off areas large enough to accommodate several vehicles. The hope, of course, is that the pull-offs won't get a lot of use. Electronic signs that post advisory speed limits have been successful in reducing congestion-related crashes in Europe, Thompson said.

"And with these managed lane signs, really what you're able to do is create a shoulder whenever you need it," he said. If someone's blocking the right lane, "you close the lane and that now becomes a shoulder."

But for some drivers, September is going to seem like a long way off.

"We are asking commuters to bear with us for the next six months," Thompson said. He encouraged people to carpool, take the bus, alter the times at which they travel and talk to their employers about telecommuting.

Using a federal formula that says 28 jobs are created for each million dollars in spending, MnDOT calculates that the congestion-relief projects will create 5,000 jobs. Also, the 21 large overhead signs are mostly being built by ADDCO in St. Paul, Thompson said.

Jim Foti • 612-673-4491