Grantham replaces retiring member Bill Kuhlke, of Augusta, who resigned in December after serving on the board for seven years.
State legislators from the region picked Grantham over Athens Area Chamber of Commerce President Doc Eldridge and Pat Bell, a former state representative and Jackson County Commission chairwoman, on the first ballot.
Grantham's top priority is to improve Georgia Highway 17, which connects Augusta and Savannah.
"It would assist the port of Savannah in a very favorable way," he said.
He acknowledged, though, that the DOT is short on money to do anything. Revenue from a per-gallon motor fuel tax is declining because many commuters are out of work and new cars are becoming more fuel-efficient, and the agency is cutting back after sustaining accounting and overspending problems in recent years.
"We are going to have to find monies to assist in that project," Grantham said.
A 1 percent sales tax for regional transportation projects that voters will decide on in 2012 could help solve those funding woes, he said.
Grantham is in favor of the "Brain Train," a proposed passenger rail line from Athens to Atlanta, he said.
He said he often discussed the controversial Interstate 3 proposal for a new freeway that could cut through the north Georgia mountains with then-U.S. Rep. Charlie Norwood, who proposed it, but declined to offer an opinion.
He also would not talk about turning Georgia Highway 316 into a limited-access freeway, possibly by charging a toll.
"I just reserve my opinion on that until I can get into it next week (when he takes office)," he said.
The owner of an Augusta lumber company, Grantham served two terms on the Augusta Commission, where he was on the Engineering Services Committee, which oversees transportation projects.
"I know what it's like to walk the halls of the DOT asking and begging for the money we need for road service in our community," he said.
Eldridge finished second, according to state Sen. Bill Cowsert, who nominated Eldridge and watched the votes being counted. The election was by secret ballot, and vote totals were not made public.
Each DOT board member represents one of Georgia's 13 congressional districts and is elected by state lawmakers from the district.
The 10th Congressional District includes part of Augusta, Athens and the north Georgia mountains.