A year ago when the price of gasoline reached $4 a gallon, motorists reacted by staying off the highways. Today a gallon of gas costs little more than half that record figure, but tax revenue figures show drivers have not gone back to their old habits.

The result is a sharp revenue decline in the state’s motor license fund, which is projected to be $150 million less than the $2.6 billion estimated for the year ending June 30, Rich Kirkpatrick, PennDOT spokesman, said.

“People are driving less,” he said. “Tax collections are well below estimates for the entire fiscal year,” he said.

Driving jumped in September after an abysmal summer but dipped in the fall when the economic problems started, officials said. It went up a bit in December, but down again through the first part of 2009.

The state gets 31.2 cents for every gallon of gasoline at the pumps, while the federal tax is 18.4 cents.

A PennDOT pie chart shows 60 percent of the motor license fund comes from fuels taxes.

Licenses and fees account for 25 percent, while 15 percent is from fines, penalties and interest earnings and income from the turnpike.

A part of the $150,000 deficit is a decline in interest earnings, Kirkpatrick said.

The gas tax has not been increased in 15 years, and it has been more than a decade since the federal government last increased its revenue to the state, said Tom Prestash, executive for PennDOT District 9, which oversees Cambria, Somerset, Bedford, Blair, Huntingdon and Fulton counties.

Meanwhile, the state’s transportation department finds itself in what Prestash calls the “perfect storm,” unchanged funding levels, sharply increased costs and highways and bridges needing repair.

Over the past decade, costs of highway and bridge work have doubled, with the biggest increase in the past two years when costs increased by 36 percent, he said.

The result is diminished buying power for some of the greatest bridge and highway needs in the nation.

“It’s no surprise, we’re not building new highways anymore, we’re preserving our existing right of way and addressing safety concerns,” Prestash said. “You won’t see PennDOT building from two lane to four lane anymore.”

Pennsylvania has the fifth largest state-maintained highway network. It ranks third in bridges, Kirkpatrick said.

While efforts are being made to improve the bridge situation, Pennsylvania has the nation’s greatest number of bridges over 75 years old.

The figure is 5,911. Kirkpatrick said that while they are safe to travel, conditions are monitored and they will need attention.

“Pennsylvania is making a concerted effort to deal with it,” he said of the deficient bridge numbers, down from 6,034 of a few years ago.

Transportation officials are keeping an eye on potentially greater problems with federal funds.

The decline in driving has had a negative impact at the federal level where lower gasoline tax dollars are creating problems with the federal Highway Trust Fund, a source of more than $1.7 million to Pennsylvania in 2007, PennDOT officials said.

A new surface transportation bill is due in Congress by Oct. 1, something that takes a couple years to put into place, Kirkpatrick said.

Yet another concern is the impact on gas tax revenue with the push for more fuel-efficient cars. If all cars reach a 35 mile per gallon threshold, the state will lose $624 million in gas taxes annually, Prestash said.

Clouding the overall funding picture is the $1 billion in stimulus money set to be spent on shovel-ready projects from the federal government.

The one-time injection puts 2009-2010 total state transportation revenue levels at nearly $3 billion and will allow for a lot of quick work, but it is not a long term fix, officials said.