In recent years, Sacramento officials have systematically bulked up and modernized key interchanges on the busy Highway 50 corridor.

Now, it's Watt Avenue's turn.

Sacramento County, working in partnership with the state Department of Transportation, on Tuesday launched a two-year, $22.5 million Watt interchange remake. Officials say it will turn one of the region's busiest commute sites into one of the most modern in the state.

Watt Avenue will get two new regular lanes in each direction over the freeway, and two new short-distance lanes, making it the widest overpass in Sacramento. Also, the interchange's cramped and outdated onramps and offramps will be removed and replaced with a higher-capacity modern design.

Notably, the new design will eliminate the dangerous merge ramps on the eastbound side, which force drivers into NASCAR-style bumper-to-bumper lane changes in a short distance.

County Supervisor Susan Peters lauded that change alone as an important upgrade.

"We lose the need to weave!" she said Tuesday at a freewayside ceremony inaugurating the project.

The interchange overhaul also contains two unusual amenities aimed at getting more people to walk, ride bikes or take buses. Bicyclists and pedestrians on Watt Avenue no longer will have to run the gantlet of fast-moving traffic to cross the freeway. The project will create a separate biking and walking path that uses tunnels under the on- and offramps.

The project also includes what's being billed as a first for California: Crews will construct a separate, walled-off lane in the middle of the overpass for buses.

That guideway will allow Sacramento Regional Transit to take a first step toward offering what is called bus rapid transit in the Watt Avenue corridor, where buses, at points, will avoid dealing with car congestion.

"Traffic can be stopped, and the buses go flying by," said RT General Manager Mike Wiley.

Bus rapid transit represents a hybrid transit approach, faster than regular buses that travel in car lanes, but more flexible and less expensive to build than light-rail lines.

The Watt Avenue corridor, already crowded with an estimated 80,000 vehicles a day, is expected to have to handle more traffic in the next decade as more development occurs on South Watt Avenue north of Elk Grove.

Wiley said he hopes eventually to extend the bus rapid transit concept to other parts of Watt Avenue. Space is limited, however. The guideway on the Watt Avenue overpass has room for only one bus lane. Buses will have to be scheduled so that two buses coming in opposite directions are not trying to cross the bridge at the same time.

County Supervisor Don Nottoli called the Watt project the culmination of 10 years' worth of Highway 50 improvements.

"This is the icing on the cake," Nottoli said.

Construction will last until fall 2014. Much of the work on the bridge will involve filling in the gap between the two existing viaducts, creating room for the two new car lanes and the bus rapid transit guideway.

Crews will work mainly during off-peak traffic hours. Lane closures are expected during nights, but plans are to keep all lanes open during commute hours, officials said.

Project funding will come from several sources, including state infrastructure bonds and county transportation sales tax revenues.

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