Work resumed this week on a project to widen College Avenue under Highway 101 after a design error caused a two-month delay.

Crews on Thursday were grading the westbound lanes of the road to prepare for paving to begin in early November. The westbound lanes were supposed to have been completed in August with work on the eastbound half of the road wrapping up about now. But the delay to the $6.7 million project means construction will continue into the spring, Caltrans spokesman Allyn Amsk said.

Engineers in early August noticed that the westbound road and sidewalks were too low and would have required steep driveways to connect to businesses fronting West College Avenue, Amsk said. The redesigned project will raise the road 1 to 2 feet in places, he said.

“The sidewalks will be built where they are supposed to be built,” he said. “The driveways will work as they are supposed to. The problem we had was a height separation between the sidewalk and parking lots.”

A conversion error from metric units to English units was partly to blame for the problem, Amsk said. The project, originally designed nine years ago as part of the Highway 101 widening project that created carpool lanes from Highway 12 to Steele Lane, was put on hold until this year because of a lack of funds.

Both the Highway 101 and College Avenue projects were designed in metric units, which Caltrans had been using, in response to federal pressure, since 1993. But in 2006, the department switched back to English units for its projects.

“The metric conversion complicated the effort to ensure accuracy,” Amsk said. “There was a discrepancy between what was designed and what was later observed in the field. There was a design error no matter how you look at it.”

Amsk did not have an estimate of how much the error will add to the project’s cost. Santa Rosa contributed $300,000 for property acquired for the project.

Caltrans expects the project to reduce congestion and improve traffic at highway ramps and on College Avenue between Cleveland Avenue and Morgan Avenue. Improvements include new bicycle lanes and pedestrian sidewalks in both directions and a second left turn lane for the eastbound College Avenue approach to the northbound Highway 101 onramp. The right turn lane for westbound College Avenue to northbound Cleveland Avenue will be extended.

Ed Gasca, manager of the Midas station on West College Avenue, said the delay to the construction project has hurt his business but he is glad that work has restarted.

“Overall, it seems slightly higher. The level looks pretty good,” he said. “It’s a good sign to see them back at work.”