(Luz Lazo/The Washington Post)

Metro’s newest fare proposal may be one small step for harried riders who use one of its express bus routes — and one giant leap for the future of bus transportation in the Washington region.

The Metro board on Thursday approved a pilot program that will require all passengers on the Metro Extra Route 79 to pay their fare with a SmarTrip card that has been loaded with money before boarding the bus.

For the next six months, riders on that bus — which runs with limited stops from Silver Spring Metro station through Petworth and Shaw to Gallery Place in the District — will not be allowed to pay their fare with cash, or to load cash onto their card as they pass the onboard fare machine.

The short-term restriction is part of an experiment to see whether a simple change can speed up express bus service, improve reliability and draw more riders. Metro officials are trying to tackle the problem known in transit-industry parlance as “dwell time” — the time a bus spends idling with its doors open as passengers board or alight.

For an average bus, dwell time can add up to a third of its total travel time, according to research from the National Association of City Transportation Officials.

About 12 percent of trans­actions on the Metrobus system involve cash, but Metro’s data suggests that those transactions account for 24 percent of the dwell time along bus routes. Cash-free boarding may help reduce those delays.

“It is something that’s a trend in the industry,” Metro General Manager Paul J. Wiedefeld said. “But we wanted to see how that plays out here in our community, so let’s see what the pilot tells us about that.”

Riders who have only cash and no SmarTrip card will be able to use the regular 70 bus, which runs along the same route but makes more-frequent stops.

The board’s action also formally established a “Cash-Free Bus Program,” a procedural step that would make it possible to implement the new fare-payment policy on other express bus routes throughout the system in the future.

The push toward cash-free bus service could signal a desire by Metro administrators to introduce other features inherent to rapid transit service, such as preboarding payment systems, designated bus lanes and synchronized traffic signals.

Transit officials in cities around the world are trying to find ways to help buses move faster through traffic, better approximating the expediency of subway service at a small fraction of the operating and infrastructure costs.

The pilot program on the 79 express bus will begin June 24. There will be a public hearing in late September to discuss whether Metro should make the change permanent, and a Metro committee will vote in November whether to codify the payment policy on the Metro Extra 79 or other express bus routes.

According to Metro’s research, it takes seven to eight seconds for each passenger to pay with cash, compared with two to four seconds for SmarTrip card payments. For passengers trying to load their SmarTrip card with cash while boarding, the average transaction time increases to at least 10 seconds.

Those time differences seem marginal, until you multiply them by the dozens of passengers who board a bus line during each run on a route.

While board members were generally supportive of the proposal, there were concerns — and some wariness.

Board member Michael Goldman said he would like to see it extended to other bus routes if it results in a shorter bus ride. But he remains concerned about the potential for confrontations between bus drivers and riders, a problem that is on the upswing, according to recent safety data.

Will drivers need to inform riders with cash that they’re suddenly not allowed to ride the bus?

“We shouldn’t be putting bus operators in confrontational situations,” Goldman said. “So they should have clear guidance.”

Wiedefeld said Metro staff will be posted at points along the 79 bus route to educate riders about the new policy, and drivers will be trained on how to respond to confused or frustrated customers.

“We’ll figure out those issues,” Wiedefeld said.

A representative from the Riders Advisory Committee pointed out that there often is a 24-hour delay when customers use Metro’s mobile app to reload their Smar­Trip cards, a glitch in the system that could cause problems for commuters trying to avoid paying cash so they can board the 79 express.

Others expressed concern for those who use cash for most of their financial transactions, particularly poor and low-income residents who are less likely to have access to credit cards to set up automatic reloading for SmarTrip cards and or large amounts of cash to load onto a card.

“This is something we’ve always worried about for the disability community because there is a group that doesn’t have access to anything but cash,” said Phillip Posner, chairman of Metro’s Accessibility Advisory Committee. Statistically, people with disabilities are more likely to fall below the poverty level because of challenges in finding well-paying jobs.

Posner suggested Metro scale back the pilot, for example, by prohibiting people from loading cash onto their SmarTrip card while boarding, which can often be a longer and more complicated process than simply paying a single fare with cash.

But low-income people may also be the demographic that stands to gain the most from Metro’s pilot, said Aaron Villere, a senior program associate at the National Association of City Transportation Officials.

Low-income communities tend to be underserved by subways and disproportionately reliant on bus service. By making buses faster and more efficient, transit agencies can improve equity across neighborhoods and demographics.

And efforts like cash-free policies, preboarding fare payments (where riders pay at a fare machine at a bus stop before the bus arrives), and all-door boarding (letting people board through the front or back doors) can also help transit agencies save money.

“As we’re trying to attract people back to buses and improve operations and make services more efficient, the benefits won’t come from driving buses faster — they’re going to come from reducing the causes of delay,” Villere said. “That’s where the savings are. You can run more service with the same amount of money, or you can use fewer resources to run the same amount of service.”

Correction: An earlier version of this article incorrectly stated that riders without cash will be able to use the regular 70 bus. The bus can be used by riders who have cash but no SmarTrip card.