The months of Americans traveling less because of the coronavirus pandemic — whether by road, rail or air — have left states and localities that rely on gasoline taxes, fare revenue and user fees to fund their budgets facing billions in shortfalls.

That means more rutted roads will go unrepaired, outdated airport terminals will wait longer for renovation, and transit riders will wait longer for buses and trains because of service cuts as transportation officials revise their spending plans to deal with the unexpected red ink.

Experts say it will probably take years for such activities as air travel to return to normal. Meanwhile, governments will still have to figure out how to shore up aging infrastructure, alleviate traffic congestion, support mass transit and accommodate the flying public.

The Maryland Department of Transportation has proposed slashing nearly $3 billion from its six-year capital budget. The cuts include delaying $900 million in road projects and postponing construction of a $500 million baggage-handling system and terminal connection at Baltimore-Washington International Marshall Airport. The state also plans to temporarily scrap some service for commuter buses and MARC commuter trains, which have ridership hovering at about 10 percent of normal.

“Everything has been hit across our system,” Maryland Transportation Secretary Gregory Slater said. “We have to find the least amount of impact to people, but people will see and feel some of this.”

Slater said his agency is trying to avoid layoffs by scaling back in other areas. For example, roads that typically would get a new layer of asphalt might instead just have potholes patched. Road crews will mow less often.

“I think people are already starting to see grass getting a little bit longer or less litter cleanup,” Slater said.

Nationwide, 18 states and 25 localities have recently canceled or delayed transportation ­projects valued at $10.9 billion, according to the American Road & Transportation Builders Association (ARTBA).

With most governors having declared construction to be essential during the pandemic, many states took advantage of unusually light traffic during stay-at-home orders to step up paving and other work. But much of the work that continued in the spring and early summer fell under contracts signed in the one or two years before the pandemic.

Alison Black, ARTBA’s chief economist, said she was struck by a decline in new contracts awarded July 1, when most states began their new budget years. With many contracts covering longer-term work, she said, the slowdown could extend one to two years.

“We’re starting to see a little more caution in work going out,” Black said. “Some states are starting to make decisions to scale back.”

In Virginia, transportation revenue for the fiscal year that ended June 30, fell $120 million below expectations. State officials predicted in August that revenue would be $400 million short in the fiscal year that started July 1 and additional $350 million short the following year.

However, so far the Virginia Department of Transportation has no plans to delay projects.

The state and VDOT “were in a strong financial position prior to the pandemic, and flexibility in allocating funding to prioritized projects should keep Virginia moving,” VDOT spokeswoman Emily Wade said.

In North Carolina, the state’s Department of Transportation said it lost $190 million in gas tax proceeds and other revenue between late March and June. It expects to lose an additional $500 million by next summer.

In addition to laying off half of its temporary employees and consultants in the spring, the agency delayed about 150 projects, including widening 10 miles of Interstate 95 near Fayetteville. The agency pulled back on more projects in August and September, NCDOT spokesman Andrew Barksdale said.

“We’ve really had to focus these past several months on emergency repairs,” Barksdale said. “We basically had to stop spending money on new things that weren’t mission-critical.”

Transportation industry advocates are calling on Congress to provide financial aid in a second pandemic relief package. They say transportation systems are key to reviving the economy by helping businesses move freight, employees to return to work, and travelers to spend money.

The funding that the Cares Act provided in March to public transit agencies and airports is running out, officials say. Congress did not provide pandemic relief for road systems.

Postponing major projects also hits hard, transportation officials say, because it can take years and cost millions of dollars to get plans through engineering, permitting and land acquisition.

“There’s so much involved on the front end to get these projects to shovels in the ground,” said Jim Tymon, executive director of the American Association of State Highway and Transportation Officials (AASHTO). “It’s hard to see projects pushed out because the money’s not there for the construction phase.”

Airport officials say their facilities continue to struggle as air travel remains down about 70 percent. U.S. and Canadian airports expect to lose $23 billion in airline fees, parking proceeds and other revenue over the 12 months that started in March, according to Airports Council International-North America.

Airports for Tampa, San Francisco, Austin, New York, and Raleigh and Durham, N.C., have postponed terminal renovations, expansions and other projects, the trade group said.

Without expanding terminals that average 40 years old, industry officials say, already cramped security checkpoints and gate areas will feel more so as passengers return and try to practice social distancing, Airports Council President Kevin Burke said.

With air travel expected to be off for several years, he said, it’s uncertain when those expansions will happen.

“That all depends on a vaccine, passenger confidence and the economy, and those variables are changing on a daily basis,” Burke said. “All airports that need work are holding back until things look a little steadier.”

Some transportation industry advocates see a glimmer of good news, or at least a less dire outlook from the spring, when much of the economy came to a halt amid stay-at-home orders.

Traffic that plummeted by half in April has rebounded to about 90 percent of pre-pandemic levels on average nationally, according to the Federal Highway Administration. More driving means more trips to the gas station — and more gas tax revenue.

AASHTO said state transportation agencies have lost $16 billion in revenue so far this year. However, the organization has reduced its projections of a five-year shortfall to $37 billion from $50 billion.

Like Virginia, some states and cities say they’re finding ways to keep new work moving.

Kentucky transportation officials suspended $58 million worth of road resurfacing contracts in April and May. However, the state resumed awarding them in June after the initial forecast of a $162 million shortfall turned out to be $60 million, said Chuck Wolfe, a spokesman for the Kentucky Transportation Cabinet.

The state avoided slowdowns in highway work by postponing major equipment purchases, reducing grass mowing and deferring some building repairs, he said.

In the District, transportation Director Jeff Marootian said Mayor Muriel E. Bowser (D) has continued to prioritize infrastructure funding. The city is on pace to repave more roads this fiscal year than last year, he said.

“All projects we’ve had planned will continue as scheduled,” Marootian said. “We’ve been able to repave roads and rebuild sidewalks because the mayor has made it a priority for us.”

Meanwhile, some transit advocates worry that cuts by public transportation agencies will most hurt low-income residents, including in minority communities already harder hit by the pandemic. With money from the Cares Act running out, Metro and other transit agencies say they’re preparing for deep cuts, including layoffs and fewer trains, if Congress doesn’t provide more aid.

The Maryland Transit Administration announced Wednesday that it had dropped plans to reduce Baltimore-area bus service after pushback from local officials, who had complained that any route cuts would unfairly hurt residents who can’t afford to drive.

Transportation experts say it’s difficult to predict how long the pain will last, depending on how the coronavirus crisis plays out in the fall, how much some commuters continue to telework, and how long before more people feel comfortable packing onto subways, buses and airplanes.

“This is one of the largest challenges I’ve ever had to deal with,” said Slater, a 22-year MDOT veteran. “I think about it 24/7, how we can build this budget, deliver services to people who really need us, and play a part in our recovery.”