Folsom Dam Road, which passes over Folsom Dam, has been closed since 2003 because of security concerns.
The old road was used by about 20,000 drivers each day. Those drivers must now use other routes.
To make up for the closure, a new bridge is being built over the American River just downstream from the dam. The new span will connect Folsom Auburn Road north of the river to downtown, which sits south of the river.
The project is expected to be done in about a year.
"It will be here before we know it," said Rick Lorenz, Folsom public works director.
So far, two huge columns are taking shape. These will eventually support a roadway about 250 feet above the river.
The project will help businesses in the old part of Folsom, said Paula Watson, owner of Planet Earth Rising. Several shops failed after the road over the dam was closed.
"I think it will have a positive effect," said Watson, whose shop sells crystals, jewelry and clothing.