Maryland and Virginia are running out of money to pay for road and transit projects, and some experts

warn that without new taxes, tolls or partnerships with private companies, it won't be long before the states can't afford to plug potholes.

Maryland spends about $1 billion a year building and maintaining transportation infrastructure, while Virginia budgeted $4.9 billion caring for its airports and 60,000 miles of roads this year.

Source: American Petroleum Institute, October 2012

State gas taxes
State Gas* Diesel*
D.C. 23.5 23.5
Georgia 28.6 31.8
Kentucky 29.9 26.9
Maryland 23.5 24.3
Massachusetts 23.5 23.5
New Jersey 14.5 17.5
New York 51.3 50.3
North Carolina 37.5 37.5
Pennsylvania 32.3 39.2
South Carolina 16.8 16.8
Tennessee 21.4 18.4
Virginia 17.5 17.5
West Virginia 33.4 32.1
All states avg. 30.9 30.1
* numbers in cents

But both states have lengthy backlogs of unfunded projects. Building each Maryland county's top priority project -- for Prince George's County, the planned Purple Line light rail, and for Montgomery County, the Corridor Cities Transitway rapid bus system -- would require $12 billion. On Interstate 95, Virginia has $12 billion in needed improvements but only $2 billion available over the next 25 years to pay for them, according to the Virginia Department of Transportation.

By 2017, Virginia will have just enough in its transportation trust fund to cover road fixes with nothing left for new projects. Maryland could run out of money to perform basic maintenance by 2018, according to the General Assembly's Office of Policy Analysis.

"There are maintenance projects already being deferred that are going to cost us more to fix in the long term," said Richard Parsons, president of the Suburban Maryland Transportation Alliance.

Though elected officials recognize that transportation funding is a problem, they are far from a solution.

Virginia Gov. Bob McDonnell warned lawmakers last week that he will ask them "to do what's necessary to address this maintenance deficit" in the 2013 legislative session.

This year, he floated a plan to increase the transportation share of the sales tax from 0.5 percent to 0.75 percent. That was rejected by Senate Democrats, who unsuccessfully lobbied for an increase in the gasoline tax.

Neither plan would have been enough to make a significant dent in the funding hole, said Bob Chase, president of the Northern Virginia Transportation Alliance.

Virginia state Sen. John Watkins announced his own proposal last week that would raise $740 million, largely by imposing a 5 percent tax on wholesale gasoline.

Though Maryland Gov. Martin O'Malley proposed raising his state's 23.5-cent-per-gallon gas tax this spring, the idea didn't gain steam. Elected officials in Montgomery County have begun lobbying Annapolis for the ability to pass their own gas or sales tax.

Lacking support for tax increases, officials have turned to public-private partnerships to pay for projects like the streetcar line and the Capital Beltway high-occupancy toll lanes, which opened Saturday

in Virginia. Maryland officials also pointed to the partnerships -- in which private companies design, build, finance, operate and maintain whole projects -- as a way to pay for projects like the $1.9 billion Purple Line.

But public-private partnerships are not a universal solution.

"We're not going to have public-private partnerships to fill potholes and build sidewalks and resurface the general traffic lanes," said Neil Bergsman, director of the Maryland Budget & Tax Policy Institute. "We have to swallow hard and raise the gas tax."

Local experts and advocates said the dearth of funds translates to an inability to prevent the region's already infamous traffic problems from getting worse -- a fate that could damage the local economy.

Virginia residents and businesses lose an estimated $3.7 billion a year from time spent in traffic, according to the Virginia Senate Finance Committee, causing a slip in CNBC's annual "Top States for Business" rankings.

The Washington region's traffic problems were the worst in the country last year, according to the Texas Transportation Institute's 2011 Urban Mobility Report, which estimated each commuter in the region loses nearly $1,500 a year.

"We all have a transportation premium in our lives when we live in an area that is among the most congested in the United States," said Lon Anderson, a spokesman for AAA Mid-Atlantic.