After years of talk, action has started on the extension of Devlin Road, a key route for travelers in the south county.

For the next several weeks, trucks will build a section of a bridge over railroad tracks north of Green Island Road, using soil from a hill near Napa County Airport.

The stretch of Devlin Road from Green Island Road to South Kelly Road is a

$7.8 million project expected to alleviate traffic congestion on Highway 29. Ultimately, Devlin Road — which now goes from Soscol Ferry Road near the Butler Bridge to Airport Road, will stretch uninterrupted to Green Island. The estimated date of completion is 2018.

Money for the project, both today’s work and future construction, is coming from developer fees. For example, the developer of the proposed Napa Pipe project — the 154-acre residential and mixed-use project south of Napa  — might end up paying for the improvements to the intersection of Soscol Ferry Road and Devlin.

In American Canyon, a city-sponsored traffic circulation committee has been convened to discuss ways to pay for a series of traffic circulation improvements, including the extension of Devlin Road into the city.

For now, Headwaters Development Co. is using the fill dirt to construct the first segments of the bridge. The Sacramento-based developer wants to build a 645,000 square-foot wine storage warehouse on about

40 acres north of Green Island. While the land is slated to be annexed into the city in the near future, the property remains under Napa County’s jurisdiction.

In separate interviews, a Headwaters representative and the airport manager said the roadwork is a good for both sides.

Napa County Airport needed to lower the hillside near the airport by 15 feet to install a new instrument landing system that allows pilots to land safely in inclement weather. The Federal Aviation Administration, which is installing the system, determined that the hill was too high and interfered with the signal, explained Martin Pehl, Napa County Airport manager.

The problem was neither the airport nor the FAA had $750,000 to haul the dirt to lower the hillside by 15 feet.

“It’s something we’ve been working on for years,” Pehl said. “You just don’t go out and knock down hills.”

In late September, dozens of trucks began hauling 118,000 cubic yards from the hillside off Green Island Road to the Headwaters property about 1.2 miles away. The approaches to the future bridge are scheduled to be completed by Dec. 1.

The bridge may be installed in the spring, said Steve Greenhagen, construction manager for Headwaters.  That company had to obtain approvals from a variety of agencies, including the city of American Canyon and the Giovannoni trust, the owners of a parcel neighboring the Headwaters’ property. It will also be responsible for patching up Green Island Road.

Doug Pope, managing member of Headwaters Development Co., said that segment of Devlin Road will be built by next summer to give Headwaters access to its property.