A $9.7 million project to widen Route 28 on the county's eastern edge is expected to be completed earlier than expected this month, easing the way for commuters by tripling the number of lanes from two to six.

After more than 18 months of work, the 3.25-mile part of Route 28 from Route 7 to Sterling Boulevard (Route 846) will have turning lanes, new shoulders and four traffic lights, said state Department of Transportation officials.

The biggest benefactors of the improvements will be commuters, who now contend with backed-up traffic because of the narrow road. "It's going to speed up their commute quite a bit," said Donald Silies, the project engineer.

The Route 28 project and the installation of a new bridge on Route 15 are the two county road improvements slated for completion this fall.

Both were needed because of a steady increase in traffic in recent years, officials said.

Two other projects on Route 28 in Loudoun, an interchange at Route 7 and a widening of a 3.4-mile stretch from Sterling Boulevard to Route 50, and a third one in Fairfax County, are expected to be finished by next summer.

By July, Route 28 will be a major six-lane road for 14.3 miles from the north, at Route 7 in Loudoun, to the south, at Interstate 66 in Fairfax County, DOT officials said.

The cost of improving the entire stretch is expected to be more than $120 million, officials said.

Located near Dulles International Airport, Route 28 is considered essential by planners and developers to accommodate growth in one of the hottest development spots in the area. It had to be upgraded from a rural road to a suburban highway.

Although more modest in scale, the opening last week of a two-lane bridge on Route 15 in central Loudoun also will help ease traffic congestion in the county, said Gary Jennings, the DOT inspector who oversaw the project.

Route 15, which bisects Loudoun from north to south, is one of the county's main roads, especially for truck traffic.

Work started on the $900,000 project last November. Since June, traffic has had to stop at the bridge because the highway was reduced to one lane and DOT had to install a light.

But two lanes opened last week, and work on guard rails, drainage and other details will be finished by the end of the year, Jennings said.

The new bridge, which spans the Little River about three miles north of Gilberts Corner, replaces a truss bridge built in the 1930s, Jennings said. It has a smoother surface and a wider roadway than the old bridge, which was built by the Civilian Conservation Corps, Jennings said.

The steel truss bridge had to be replaced because it was rusting and breaking free from its abutments, in large part because of increasing car and tractor-trailer traffic, he said. The repair costs also began to mount, he said.

"It wasn't built for traffic . . . . It was rusted real bad," Jennings said. "You will notice the difference."

Other DOT projects for Loudoun County include:

A new bridge over Goose Creek on Route 7 east. The project is expected to cost $2.1 million and be completed March 1, said Mary Anne Reynolds, a DOT spokeswoman.

Improvements on a 1.8 mile stretch of Ashburn Road between Route 7 and Route 647. The project, which will add a lane to the road south of Route 7, is expected to cost $2.2 million and be completed next June, she said.

A widening of a half-mile of Waxpool Road west of Route 28. The project will double the lanes of Waxpool Road from two to four at a cost of $727,000. It is expected to be completed by May, she said.