With congestion rapidly spreading on Maryland's roads, a commission appointed by Gov. Parris N. Glendening has warned that the state must spend at least $27 billion more than now planned over the next two decades to prevent traffic from growing significantly worse.

But even that huge increase would provide only sporadic and often short-lived relief in the specific areas where improvements are made, and additional traffic jams are inevitable, according to officials and traffic projections.

"This region is going to face some really tough congestion in 20 years even with the [recommended] funding being provided. It's probably a matter of degree how much worse it's going to get," said William K. Hellmann, a former state transportation secretary and co-chairman of the commission, which completed its final report this month.

Commission members concede that the $27 billion goal is probably unrealistic and say the state should aim for nearly two-thirds of that sum, or $17 billion, an amount that still would likely require new taxes or fees to pay for road, transit, airport and seaport improvements.

The commission's findings that Maryland will be unable to buy its way out of congestion have been taken by engineers and planners as the latest evidence that the state must turn to more innovative solutions. These include: a closer link between transportation and land-use planning; financial incentives for living and working near transit stations; and a more aggressive economic development campaign in older suburbs, such as inside-the-Beltway communities in Montgomery and Prince George's counties.

"For the first time, they began to link the need for land use with transportation, but they're still focused largely on building our way out of the problem," said commission member Dru Schmidt-Perkins, executive director of 1000 Friends of Maryland, a prominent environmental group. "In 20 years, my son now just going to college will be sitting in a hearing room looking at the same situation but so much worse."

The commission's report--which sets the table for an anticipated debate over transportation funding when the legislature returns in January--identifies a $13.3 billion shortfall for expanding highways across the state, including $12 billion for the eight counties in the Washington suburbs. An additional $2.1 billion is needed to maintain roads.

On the transit side, the panel calls for $6.1 billion to expand rail and bus service--about half that would go to the Washington area--and $1.5 billion more to run the systems. This investment is designed to nearly double the number of daily transit riders to 1 million over the next 20 years.

Yet with motorists in Maryland projected to drive almost 50 percent more in 2020 than they do now, top transportation officials caution that even a mammoth increase in spending cannot turn the tide. "Will overall congestion statewide be less than today?" asked Transportation Secretary John D. Porcari. "I don't think anyone is predicting it will be less."

Some of the five dozen highway projects earmarked for funding would no doubt provide sustained and long-overdue relief during the coming decades, such as the widening of Route 210 in Prince George's County south of the Beltway and Route 237 in St. Mary's County.

State projections show, however, that other widened highways would be filled to capacity--or even overwhelmed--within two decades. In Prince George's, traffic on Branch Avenue that already backs up badly at rush hour is expected to more than double over the next 20 years as booming development continues in the southern part of the county and Southern Maryland. "Whatever else is done on Branch Avenue, we're going to do the best in our ability to make improvements to meet the traffic demand in 2020," said Betty Hager Francis, county public works director. But in fact the proposed conversion of the road to a six-lane expressway still would fall far short of handling the flood of new cars, according to state estimates.

In Montgomery County, traffic on Route 28 in North Potomac could be up to 40 percent over capacity even after the road is expanded from two to four lanes. A similar widening project on Route 124 north of Gaithersburg would be outstripped by traffic by 2020.

This summer, Montgomery planners reached a sobering conclusion when they evaluated a 20-year county transportation plan that officials say embodies most of the projects included in the statewide commission's report. Although the program would more than triple the spending planned for roads and transit, traffic tie-ups still would get worse. The proportion of county roads with congestion would increase by 75 percent. Average speeds would drop by 5 mph.

Nor is the news more heartening in the outer counties. Howard County officials welcome the proposed construction of a new interchange on Columbia Pike at Johns Hopkins-Gorman Road, saying this would eliminate a major bottleneck. But backups on the highway are projected to continue because there are no plans to widen the roads surrounding the interchange.

In Calvert County, likewise, a new interchange is planned for Route 4 at Route 60. But county officials say that with no plans to widen Route 4 itself, traffic will "seriously deteriorate" to stop-and-go. Nor would the proposed widening of Solomons Island Road, which carries Routes 2 and 4, keep pace with rapid commercial development in the Prince Frederick area.

As bad as congestion will get, commission members said the state will not be able to pay for the investments unless it considers raising taxes--by a lot.

"If we're going to do our best to keep up, we're talking about a revenue increase that's much, much larger than Maryland has ever had to face before," Hellmann said. "That's going to be difficult for legislators to deal with. They've never had to deal with something of this magnitude."

Take the proposal last month by House Speaker Casper R. Taylor Jr. (D-Allegany) to devote 1 cent of the current 5-cent sales tax to transportation. That reallocation would be phased in over 10 years and raise nearly $8 billion by 2020--not even a third of the cash needed. Taylor said he also will support a tax increase for transportation if his initiative fails to generate enough money.

Key legislators agreed that raising transportation money would require tapping sources beyond the traditional gas and titling taxes. Increasing the gas tax by 10 cents a gallon would yield about $5.6 billion over 20 years. Moreover, Glendening (D) has promised no gas tax increase for the next three years. Raising the titling tax 1 percentage point would generate less than $2 billion.

Increasing the sales tax by a penny to 6 cents would raise more than $10 billion, but many legislators are wary of raising it so abruptly or dedicating this statewide revenue specifically for transportation. Also on the table is a proposal to add a regional sales tax levy of 1 cent in Montgomery and Prince George's counties and the Baltimore area to support mass transit. If the tax base remains constant, that would raise almost $5 billion, legislative staff members said.

Although Sen. Barbara A. Hoffman, influential chairman of the Senate Budget and Taxation Committee, said she objects to dedicating general taxes for transportation, she echoed other legislators who said the state will have to look to a range of gas, transit and sales taxes. "You probably need to do a little bit of everything," said Hoffman (D-Baltimore).

Everything, planners said, must also include shifts in land-use and transportation policy designed to tame the rise in driving.

Richard C. Hawthorne, Montgomery's chief transportation planner, said the pessimistic conclusions of the county's analysis this summer underscored the need for initiatives to encourage transit use, for instance by experimenting with more favorable fares and limiting the amount of parking around office buildings that can be reached by rail and bus. Hawthorne and other officials, including Porcari, said the state also should use financial incentives, such as tax breaks and mortgage subsidies, to channel development to areas near train stations.

"The investment part of the equation is only going to do so much," said John P. Davey, commission co-chairman. "To really make a significant impact on congestion, we have to make some policy changes as well."

Miles to Go

The state Commission on Transportation Investment found that Maryland has $27 billion in unfunded needs through 2020.

Highways: $15.43 billion

Interstates $5.74 billion

Other roads $7.56 billion

Maintenance $2.13 billion

Mass Transit: $7.57 billion

MARC and other

Maryland Transportion

Administration projects: $2.81 billion

Washington Metropolitan Area

Transit Authority projects: $3.26 billion

Transit operating expenses: $1.50 billion

Aviation, $3.21 billion

including Baltimore-Washington

International Airport

Maryland Port Administration: $1.88 billion

Motor Vehicle Administration: $193 million

SUBTOTAL: $28.3 billion

MINUS: Future funds available from existing sources.

- $1.3 billion

Total unfunded needs: $27 billion

To raise $27 billion over 20 years, or an average of $1.35 billion a year, the state would likely have to raise taxes. Here are some examples of how much various taxes would have to go up to generate the money, assuming no other revenue was forthcoming.

Increase the corporation income tax rate to 35% (currently 7%)

Increase the vehicle titling tax rate to 19% (currently 5%)

Increase the gas tax to 71 cents per gallon (currently Maryland tax is 23 cents)

Increase the sales tax to 7.5 cents per dollar (currently 5 cents per dollar)

SOURCE: Maryland Department of Transportation, and Washington Post analysis