The MBTA wants to go cashless. What about people who might be left behind?

On some MBTA bus lines, as many as 20 percent of the riders pay with cash when they board a bus.Jessica Rinaldi/Globe Staff/Globe Staff

The MBTA’s plan to institute cashless fare payments is good news for the harried commuter tired of waiting for the person in front to search for change to get on board.

But what about riders — mainly low-income and the elderly — who don’t have credit cards or aren’t comfortable with smartphones? There is growing concern that the new system could be inaccessible for them.

The changes are part of a newly adopted $723 million contract to implement a fare- collection system that transit officials laud as a critical move to modernize the Massachusetts Bay Transportation Authority.

Under the system, due to be in place by 2020, riders will not be allowed to pay with cash on board buses, trolleys, or commuter trains. Instead, the T will have vending machines at bus stops and outdoor trolley stops, where riders can use cash to load rides onto a new type of CharlieCard that’s being developed.

The authority also plans to increase the number of retailers that sell and reload the cards.

However, many of the bus lines that have a high number of cash-paying riders have dozens of stops, and the T has acknowledged it will not be able to place vending machines at each one.

Kimberli Gutierrez, a Salem State University junior, worries that her grandmother in East Boston will have trouble with the new system.

“My grandmother, she does have an iPhone, but she struggles every day to use it or even get in it, and she doesn’t speak English well, and she doesn’t have a credit card,” Gutierrez said. “People like that will struggle. I’m young, I have a credit card and Apple Pay, but there are people who are not basing their lives on technology.”

The T wants to eliminate on-board cash payments because they can slow boarding and cause delays. Buses overall have the worst on-time performance records among the T’s transit modes, and on some bus routes 20 percent of the riders pay cash when they board.

So the MBTA will install electronic readers that can scan CharlieCards, as well as credit cards and smartphone payment apps. Buses and trolleys will have the devices at the front and rear doors, which should also speed up boarding and improve on-time performance.

Overall, only 7 percent of MBTA bus and trolley riders pay with cash, but many are low-income and immigrants, who, for a variety of reasons, do not or cannot have a bank account or a credit card, said Kimberly Barzola, an organizer for the T Riders Union, an advocacy group.

“It’s unlikely there’s going to be a vending machine at every single stop,” Barzola said. “These investments on the T are long overdue, but we don’t want to do it at the expense of riders who are unable to pay electronically, for whatever reason — they don’t have the credit to open up an account or maybe their citizenship status doesn’t allow them to.”

To encourage riders to keep track of their CharlieCards and reduce the cost of replacements, the T also plans to charge for the new cards, probably about $5.

That bothers T rider Candelaria Cordova. She said that being able to use cash on the bus comes in handy when she forgets her CharlieCard or if there is an unforeseen circumstance, such as the time her card split and the electronic reader on the bus could not scan it. Under the new system, she would have to pay $5 for a replacement card.

“So each time that happens people will have to pay $5, plus the fare?” Cordova said. “It’s not right.”

David Block-Schachter, the MBTA’s chief technology officer, said the authority will ensure that vending machines are installed at key bus stops and will make CharlieCards available for purchase and loading through “a greatly expanded retail network” that includes big-box chain stores and mom-and-pop businesses, such as bodegas and barbershops.

The machines will also have multiple language options.

“This is about removing cash from on board vehicles, not removing cash from the system as a whole,” Block-Schachter said. Having “cash payments on board vehicles [makes it] difficult or impossible for us to move toward all-door boarding, the largest improvement we can make for our bus customers.”

The T said it will also work to distribute free cards to low-income residents, though that may not immediately help the occasional passenger who has lost one.

The bus routes with the highest percentage of cash on board customers are the 465, which travels between Danvers and Salem, according to the T, the 429 between Revere and Lynn, and the 217 between Quincy and Ashmont in Dorchester. Roughly one in five of the riders pay in cash.

In a spring survey, the T found that about 4 percent of passengers don’t have a debit or credit card or a smartphone. Of those, half are minorities, and more than three-quarters pay in cash or get passes from an employer or school.

Ultimately, the new system should save money for cash customers and those who use the paper CharlieTicket; they now pay a premium of 50 cents more per subway ride and 30 cents more on the bus. The new system will do away with that penalty, said Monica Tibbits-Nutt, of the MBTA’s Fiscal and Management Control Board.

“Right now the options are limited if you don’t live near a station where you can add that cash to the CharlieCard; you really actually have no choice but to pay with cash on the bus itself,” Tibbits-Nutt said. “What we’re trying to do is take that out and make that network so vast that you can add that cash to the card and be able to go on the bus at that lower rate.”

The MBTA has had limited success with arrangements with retailers to reload passes. Many dropped out because they earned just 1.8 percent as a commission. Currently, 160 retailers still provide that service for the T, mostly around commuter rail stations.

Block-Schachter said the new fare vendor, California-based Cubic Corp., will negotiate with retailers and will have to meet certain performance standards, including ensuring that the vast majority of T riders have ready access to a vending machine or a retailer.

For riders, it will be as simple as buying “a phone card at your local bodega and putting $20 into it,” Block-Schachter said.

Proximity to vendors and kiosks will be key, said Carolyn Villers, executive director of the Massachusetts Senior Action Council, which works with low-income seniors.

“People at the end or start of bus lines might have more access to vendors, retailers, or the machines, but a bus system travels a lot of ground that people wouldn’t have access” to payment systems, Villers said.

“When you’re working with very limited income, you can’t always plan ahead and put money on the card because you may need that for something else,’’ she said. “To take the drivers out of that situation of having to collect fares and things of that sort, I think it’s going to continue to cause challenges for people.”