By 2030, Charleston traffic could be as thick as the current congestion in Atlanta unless the state road building program keeps pace with expected population growth, according to a study released Wednesday.

Vehicle travel in South Carolina increased 49 percent from 1990 to 2007, and it is expected to grow another 45 percent by 2025. The state's population, 4.48 million in 2008, increased 28 percent since 1990, and is expected to grow another 15 percent by 2030, says the The Road Information Project, a national nonprofit transportation research group.

"It is critical that the state adequately fund its transportation system and that Congress produces a timely and adequately funded federal surface transportation program this year," said William M. Wilkins, TRIP executive director.

The American Recovery and Reinvestment Act provides about $463 million in stimulus funding for highway and bridge improvements in South Carolina. The money is a down payment on needed highway and bridge work, but it is not enough to get the job done of bringing the transportation infrastructure up to where it needs to be, the report states.

"With every year that passes, South Carolina's highway infrastructure deteriorates more and more, and every year construction costs to repair and maintain our state's highways, roads and bridges increase, yet it has been two decades since policy makers have increased the revenue base that supports highway improvements," said Scott Fant, board chairman of the South Carolina Alliance to Fix Roads.

A strained road program can mean delayed maintenance that translates to higher costs for drivers. Driving on bad roads costs a state resident an average of $262 annually in repair costs and increased fuel consumption and tire wear, the report states.

"There's definitely some big potholes. I think it depends on the area. I'm fortunate that I don't have to get on the Interstate," said Colleen Delaney, who lives and works in Mount Pleasant.

Currently, South Carolina has the fourth highest traffic fatality rate in the country. The death rate is five times higher on rural roads. Twenty-eight percent of the state's roads are in poor or mediocre condition, and 20 percent of its bridges are structurally deficient or functionally obsolete, the report states.

"When we talk about the health of our state's overall business climate, poor infrastructure negatively impacts South Carolina as companies decide whether or not to locate or expand here," said Otis B. Rawl Jr., president and chief executive officer of the South Carolina Chamber of Commerce.

David Secrest of North Charleston said he is excited about the ongoing widening of Interstate 26.

He said that widening Ashley Phosphate Road from four lanes to six lanes has made a huge difference in traffic flow.

"There's definitely some areas that could be quite a bit better," he said.

From 1998 to 2007, South Carolina received $5.3 billion in federal funding for road, highway and bridge improvements, which was 56 percent of revenues used annually by the state to pay for the work. The current federal transportation program expires on Sept. 30, requiring Congress to authorize a new program or extend the current program to allow federal transportation dollars to continue to flow into South Carolina.

However, recent declines in federal transportation revenues and significant increases in the cost of construction materials will make it more difficult for Congress to provide adequate funds for the nation's transportation system, the report states.

The National Surface Transportation Infrastructure Financing Commission has recommended a new charge on motorists based on the number of miles driven.

It also has recommended that the federal motor fuel tax be boosted in the short-term but phased out as the mileage-based transportation fee is fully implemented in 2020.