PITTSBURG -- Environmental studies are rolling forward for a long-sought expressway that would cut through steep terrain south of the city while alleviating local traffic bottlenecks.

The public is invited to vet documents for the James Donlon Extension, a 1.7-mile road that would run from the western edge of Discovery Builders' planned Sky Ranch II subdivision to Kirker Pass Road. James Donlon Boulevard dead-ends at Antioch's western border, the road built as part of a housing development by the Seeno company.

Pittsburg released a draft version of an environmental impact report earlier this month. Comments on the plan will be accepted until May 29.

Originally added to Pittsburg's General Plan in 1980, the estimated $50 million, two-lane road is viewed as a key route to take commuters to central Contra Costa from Antioch and farther east, pulling them off of Buchanan Road.

"They would be the primary beneficiaries," Mayor Nancy Parent said. "I think if you asked drivers from Antioch if they would prefer to go that way and never have to go down Buchanan, they would say yes."

Local drivers say Buchanan traffic constantly backs up during commute hours because of its tight intersections and the steady flow of merging cars from schools and neighborhoods onto the already-cramped road.

A study on the extension was completed in 1993, but details of the road's alignment were not explored, according to city engineers. Pittsburg conducted a more thorough initial environmental look in 2007.

In addition to identifying a definite road path, the latest draft adds a median, curbs and sidewalks to a near half-mile stretch of Kirker Pass from Nortonville Road to the Pittsburg city line. A free right turn lane from Kirker Pass onto James Donlon would be added, along with an approach on the west side of Kirker Pass for the future Montreaux Drive.

Documents identify several "potentially significant" effects, including aesthetics, biological resources, geology and soils, noise and air quality. The study also addresses landslide prevention, crossing seasonal stream beds and the likely relocation and raising of PG&E transmission lines.

Alternatives such as widening Buchanan and creating a James Donlon road alignment farther north were considered in the study. However, widening Buchanan would require right-of-way acquisition of 66 properties, while the north alignment would increase effects on noise, geology and air quality, according to the plan.

The regional environmental group Save Mount Diablo is among those that plan to submit comments outlining concerns.

Seth Adams, the group's land program director, said construction would require drastic "cuts and fills" and extensive grading for the sloping hills and half-dozen canyons in the vicinity, destroying some of the most pristine land in the region.

Approximately 2.1 million cubic yards of grading would be required for the roadway, according to city documents. Adams said Pittsburg is underestimating the scope and cost of the project.

The project's path would also bisect the Thomas Ranch property, where the pioneering Contra Costa family has raised cattle since the 1860s -- long before Pittsburg became a city. Pittsburg would likely have to use eminent domain to acquire right-of-way.

After assessing the environmental challenges, Pittsburg will have to figure out how to pay for the project and work with the county's Local Agency Formation Commission on annexation.

Contact Paul Burgarino at 925-779-7164. Follow him at Twitter.com/paulburgarino.

IF YOU GO
What: Public workshop on James Donlon Extension
When: 5:30 to 7 p.m. May 22.
Where: Pittsburg City Hall, 65 Civic Ave.
Information: The environmental report is available on the city's website, www.ci.pittsburg.ca.us. Written comments can be sent to city planner Leigha Schmidt or emailed to her at lschmidt@ci.pittsburg.ca.us.