PORTLAND (AP) — Oregon stands to come up short $1 billion between actual spending and state transportation needs over the next 25 years, according to the updated Oregon Transportation Plan.

According to the plan, an update of a 1992 document, the state’s 24-cent-a-gallon gasoline tax would have to double just to keep the state’s road system in today’s mediocre shape.

The plan, which offers strategies for the next quarter-century, gets its first public airing next week.

“Here it is in a nutshell: If we continue to do business as usual, with funding as usual, our transportation system is going to grind to a halt,” said Oregon Transportation Commissioner Gail Achterman, who heads the plan’s steering committee.

The plan explores the future of Oregon’s airports, bicycle and pedestrian facilities, pipelines, ports, waterways and railroads, highways, local roads and public transportation systems.

The extra capacity originally built into the state transportation plan is mostly used up.

The plan paints a future that without major changes looks even worse than the present. Congestion undermines economic growth. Roads continue to deteriorate, and the quality of transit service suffers.

Highway crashes kill or injure thousands. And the state’s road-financing system fails to maintain the existing network, let alone pay for needed investments.

Other challenges include an increasingly competitive global economy, an uncertain oil supply and the terrorist threat.

The plan analyzes the implications of three investment approaches: sticking with current levels, keeping up with inflation and adding capacity.

At existing funding levels, the quality of road surfaces and public transit service would decrease, and congestion would increase, as the purchasing power of the gas tax drops by 40 percent.

The plan proposes shifting money out of transit into highway operations in 2010 when all current light-rail projects are completed.

The plan says a 1-cent-a-gallon jump in the gas tax would keep up with rising maintenance costs but do little more.

It says projects such as widening Interstate-5 from Eugene to the Columbia River would best be paid for with tolls and public-private partnerships and by capturing land value increases caused by highways or transit projects.

She said if people who need to travel only within five miles of home stayed off the freeways, the freeways wouldn’t be congested.

The public comment period ends March 1. The Oregon Transportation Commission is expected to vote on the plan next summer.