MADISON (WKOW) -- If you drive or bike into the isthmus, your commute is about to get slower.
John Nolen Drive, one of Madison's busiest arteries, will be under construction from March 29 - May 28.
The bulk of the project will take place along the causeway, from Lakeside Street to Broom Street. At times, only one lane each direction will be open. Severe delays are expected.
"We really need drivers to be alert," said Tony Fernandez, city engineer. "Pay attention to the signs, pay attention to other drivers, be courteous, have some patience."
City engineers say the causeway, built in the 1960s, is actually sinking, and there's a gap in elevation between the road and the bridges.
"Right now, you've got a pretty good thump as you go over these two bridges," Fernandez said. "We're going to level out the approach, and do some asphalt paving on either side to smooth it off."
Suggested alternative routes include Fish Hatchery Road and Park Street.
While it will be slow going for drivers, it will be a no-go for bicyclists, roller bladers, and walkers.
"It's going to be a bridge-out situation, you're going to have to turn around or swim."
The capital city trail will be closed the entire duration of the project. People will have to take a marked detour west around Monona Bay.
When completed, engineers say, the capital city path will be wider, and safer.
"We're not going to actually widen the bridge, but we're going to take the railing and move it out a little, so we'll get an extra foot on the bridge," Fernandez said.
There is a financial incentive for the contractor to finish the project early -- they get an extra $2,000 for every day it's done ahead of schedule, -- but they'll have to pay a $2,000 penalty for every day late.