Initiatives to blunt climate change could clash with efforts to meet Virginia's transportation needs.

The reason is that alternative fuels and improved vehicle fuel efficiency could erode the main source of highway and transit money: the gas tax.

"There is a tension between the goals of mobility, accessibility and economic vitality [and] the goals of greenhouse gas reductions," state Transportation Secretary Pierce R. Homer said.

State officials worry that global warming from high levels of greenhouse gases could disrupt Virginia's agriculture, degrade the Chesapeake Bay and raise sea levels.

And transportation -- overwhelmingly from highway vehicles -- accounts for 31 percent of Virginia's greenhouse gas emissions, state Deputy Transportation Secretary Ralph Davis told the Commonwealth Transportation Board yesterday.

"Transportation policymakers need to understand . . . the risks to transportation systems of climate change," Davis said.

Flooding from higher sea levels -- an estimated 7-23 inches over the next century -- and storm surges pose the biggest threat to roads, bridges, tunnels, railroads and waterways, he said.

But, Davis said, "Every mode of transportation will be affected" by climate change.

Virginia's motor-fuels tax provides nearly 40 percent of state transportation funds, according to Reta Busher, VDOT's chief financial officer. Last year, the gas tax alone amounted to $859.5 million.

The federal government relies on the gas tax -- 17.5 cents a gallon for gas and diesel -- for 87 percent of its transportation funding, and Virginia is heavily dependent on the national level for highway and transit money.

Because Virginia taxes only gasoline and diesel fuels, cars and trucks that run on, for instance, hydrogen or electricity would escape paying fuel tax.

Meanwhile the improved fuel efficiency of modern vehicles has flattened the state's income from the gas tax, while road use has nearly doubled in the past 20 years.

"Current funding methods will not keep pace with new energy technologies used in vehicles," Davis told the board, and as a result, "the commonwealth will see a decrease in motor fuel tax revenues."

Highway-user taxes also underwrite Virginia's mass transit, rail, ports and aviation programs.

"That's such a large source of our revenue," said Commonwealth Transportation Board Member Cord A. Sterling of Stafford. "We're looking at less being done. That's where my concern is coming from."

Nationally, transportation officials are considering new revenue sources, such as taxing the number of miles a vehicle drives using GPS-based systems.

"We've got to shift our revenue stream sooner rather than later," Sterling said.

"This is the beginning of a very long conversation," Homer said. "We're not going to jump to conclusions."
Contact Peter Bacqué at (804) 649-6813 or pbacque@timesdispatch.com.