Construction likely will begin next year on a long-awaited extension of Grant's Trail after a local planning board approved setting aside $2 million for the project.

The trail currently is about 8 miles long and one of the busiest in the area with more than 750,000 users per year. It crosses south St. Louis County from the Lodge at Grant’s Trail to near a parking lot at Interstate 44 and Big Bend Road.

Some cyclists ride its length, then double back to maximize how many miles they can cover.

The two-mile trail extension will join it to the 6.5-mile-long River Des Peres Greenway, creating a roughly continuous 17-mile route for bicyclists and walkers.

The price tag: $10.2 million.

Two bridges will need to be built — one across Bayless Avenue, the other over the River Des Peres — and a tunnel will run beneath Weber Road.

Emma Klues, spokeswoman for Great Rivers Greenway, said Monday that engineering on the expansion is slated to begin this year with construction targeted to start in the summer of 2017.