An upheaval in commuting patterns is afoot as employees change when and how they return to their desks — and how often, if at all.

With more offices expected to reopen after Labor Day, transportation experts say even a small shift toward telework could lead to thousands of motorists and transit passengers vanishing from roads, trains and buses. The ability to work from home part of the day would allow more commuters to avoid the morning and evening crunch, shortening the duration of the worst congestion.

Some experts expect midweek misery if Mondays and Fridays become popular telework days, leaving Wednesdays as the in-person “meeting day.”

Changes are in motion as more workers mull whether to return to familiar commutes of early 2020 or experiment with a new routine — decisions that could have sweeping implications for mass transit and traffic congestion. Transportation officials eyeing the emerging trends say the adjustments to the region’s pandemic-era commuting patterns might be everlasting.

“The question is how fast folks come back, how frequently they come back, and whether there’s flexibility on when they can be in the office,” said Joe McAndrew, a transportation specialist for the Greater Washington Partnership, a business leadership group. “I don’t think this region will ever be the same because of the high capacity of people who can work from home.”

Many companies’ plans to rev up this summer before a broader fall reopening have seemed less certain in recent days amid a surge of the delta variant of the coronavirus.

The Centers for Disease Control and Prevention on Tuesday again recommended indoor mask-wearing in some circumstances, potentially increasing worries about sitting one cubicle away from others for hours a day. Some federal labor unions also have voiced concerns about the variant just as federal agencies — the D.C. area’s largest employer — were finalizing their back-to-the-office plans.

“If we’re gearing up for another wave in this pandemic, you can probably ask anybody, and nobody will know how this will play out for the next several months,” said John Gasparine, a transit and rail market expert at WSP USA, an engineering and consulting firm.

However, the rise of the delta variant highlights Washington-area officials’ biggest commuting concern: Calling people back to the office before they are ready to ride increasingly crowded buses and trains could lead many to drive solo, potentially canceling out any traffic relief that increased teleworking would bring. Some suburban officials have urged employers to encourage public transit usage among workers, stressing pandemic-era sanitation protocols.

“It has the potential to be a big problem if we have more traffic on the roads at the wrong times,” said Christopher Conklin, Montgomery County’s transportation director.

The pace at which parking transactions have resumed in several large cities with major mass-transit systems — New York, Boston and San Francisco — points to the possibility that more commuters are driving.

Smarking, a San Francisco-based tech company, said parking facilities it monitors in those cities are at 85 to 90 percent of their pre-pandemic levels, compared with a 74 percent average comeback in other North American cities. Parking transactions in the company’s monitored facilities in the District are about 60 percent of their pre-pandemic levels.

But many motorists aren’t renewing monthly parking passes, said Wen Sang, Smarking’s chief executive. Instead, they are asking for a more flexible price break that jibes with their new hybrid schedules.

“People say they want to pay for six to 10 days a month or a few days a week,” Sang said.

If employer-provided parking becomes more available because some workers stay home, previous Metro riders would have a new incentive to drive, officials say. Others might be more willing to pay hefty private parking fees if they only have to do so a couple times a week.

On the other hand, some experts hope that workers who commute less often also might ride a bicycle or walk — two popular pandemic pastimes.

In a study for the Greater Washington Partnership, Ernst & Young predicted that the number of workers between Richmond and Baltimore who telework a few days a week could quintuple from pre-pandemic levels. That would mean 18 percent of the total workforce — more than 1 million people — staying off roads and transit systems during morning and evening peaks several days a week.

The partnership estimates that about half of all jobs in the Richmond-to-Baltimore corridor can be done from home. That includes about 176,000 workers who commute into the District daily, McAndrew said.

“Those are the people who could be transformative,” McAndrew said.

Even a slight reduction in traffic has an outsized impact on heavily congested roads, experts say, because traffic flows freely once it drops below about 80 percent of a road’s capacity. Increasing teleworking has long been viewed as a relatively simple way to ease backups because it removes vehicles from the morning and evening rush, when road capacity is most overtaxed.

“If we can level out those peaks, even by 3 percent or 5 percent, it would have a very noticeable effect,” said Bob Pishue, a transportation analyst for INRIX, a Seattle-area firm that collects data on passenger vehicles.

This summer has been a test case for how eager — or willing — employees are to return to offices after coronavirus vaccinations became widely available. Many companies asked some workers to come in at least a couple days a week after the July 4 holiday to get comfortable with the idea.

As of July 21, office buildings served by Kastle Systems security in the D.C. area averaged about 30 percent occupancy — below the 35 percent average for its 10 largest metropolitan areas, according to the company’s tally of swipes used to access buildings.

Experts say they expect a gradual increase in commuters over the coming months, rather than a sudden rush back to the office, assuming the spread of the delta variant doesn’t push back reopenings.

A Greater Washington Partnership survey in late 2020 found that 56 percent of employers in the D.C. region, Richmond and Baltimore expected most of their workers to continue teleworking one to two days a week. Another 13 percent predicted their employees would work remotely three to four days a week.

The day after Labor Day, dubbed “Terrible Traffic Tuesday,” is considered the next back-to-the-office milestone because most schools are expected to be fully open, freeing up workers with younger children.

“That’s when the clock will start ticking on our transition to the new normal,” said Timothy Canan, planning data and research program director for the Metropolitan Washington Council of Governments.

The commuting comeback has lagged in the Washington region and several other cities with a high proportion of desk jobs and mass-transit usage, according to INRIX, the traffic analytics firm. While morning traffic volumes in car-centric cities such as Tampa and Phoenix are exceeding pre-pandemic levels, they are at 80 percent in the D.C. region, 67 percent in New York and 71 percent in San Francisco, INRIX said.

D.C.-area traffic that had plummeted by about half in March 2020 is back to about 96 percent of its pre-pandemic level overall, according to INRIX. However, traffic volumes are spread more throughout the day, revealing more flexible commute times and teleworkers escaping home computers midday to work out or run errands.

Afternoon traffic has bounced back more than in the mornings, experts say, because commuters typically tack on more personal trips, such as a grocery store run, on their way home. Traffic also can feel as bad as ever during the peak of either rush-hour period, or whenever traffic volumes outstrip a road’s capacity, experts say.

Mass transit has rebounded more slowly. But for Metro, the nation’s third-largest transit system, July offered a jolt of optimism for an agency that lost three-fourths of its riders during the pandemic.

During the week of July 11, Metrobus ran an average of nearly 197,000 daily passenger trips — 30 percent below normal but 14,000 more than the week before. Metrorail averaged about 151,000 daily passenger trips, which is 70 percent below pre-pandemic levels but 1,000 more than the previous week.

Metro General Manager Paul J. Wiedefeld said the lower ridership means the agency won’t have problems accommodating returning office workers and thousands of District schoolchildren who rely on it. To persuade them to ride, Metro has promoted a new air-filtration system in subway cars and frequent cleanings of stations, trains and buses. It plans to launch another public awareness campaign in the fall.

“Our focus continues to be to make sure people feel safe,” Wiedefeld said.

Metro’s average passenger loads have grown, in part, because of booming weekend ridership — a surprise for a transit system historically focused on weekday workers. On Sunday, July 11, for example, Metrobus recorded a 479 percent jump in trips compared to a year earlier.

Weekend ridership also is climbing more quickly on other transit systems, including on the San Francisco and New York subways, according to agency figures.

“Our theory is that weekend pandemic riders have fewer other options, leading to a faster weekend recovery,” Alicia Trost, spokeswoman for Bay Area Rapid Transit in the San Francisco area, said in an email. “Weekday ridership was clobbered by those who had the option to work from home.”

She said BART’s weekend riders tend to be younger, lower-income and less likely to have a car. Transit researchers say many also are service industry employees and part-time workers who always relied on transit, while others might be making up for a year largely spent homebound.

“Transit is filling a leisure role to a large degree, or it’s providing an important service to people who work all days of the week, not just your 9-to-5 office riders,” said Yonah Freemark, a senior research associate at the Urban Institute.

David Schrank, a senior research scientist at the Texas A&M Transportation Institute, said he expects chronic traffic congestion will eventually return, even amid more teleworking, as major metropolitan areas continue to add population and jobs.

However, he said, the pandemic will leave its mark. Still unknown are where and when new hot spots will surface as commuting patterns change, including if “office days” — and commutes — get clustered midweek.

“What happens on days when the whole workforce has to go in?” Schrank said. “It could look very pre-pandemic overnight.”