Starting Friday, some disabled residents in Boston have the option to make their subsidized travels in an Uber or Lyft car.

The popular app-based companies have partnered with the Massachusetts Bay Transportation Authority to offer paratransit customers the option of on-demand service.

The partnership, a first of its kind in the United States, is likely to become a model for transit systems across a nation pressed to reduce costs of the multimillion- dollar, heavily subsidized services available to people with special needs.

The Boston program launched Friday afternoon as a pilot responds to customer pleas for same-day, flexible and on-demand transportation that is lacking in the antiquated paratransit world, transportation officials say. Long term, they say, it would save the MBTA millions of dollars.

“It will enable the MBTA to reduce its overall expenses,” the agency’s general manager, Brian Shortsleeve, said. Boston’s door-to-door service for the disabled and elderly, known as The Ride, has a budget of over $100 million a year, and each ride costs $31, officials said. But under the new program, every Uber and Lyft ride will cost the agency $13.

“This is 70 percent cheaper than our existing service,” said Shortsleeve. “If it works, we certainly hope that we would expand it while dramatically reducing our total cost per trip.”

Transit agencies across the country, including Washington’s Metro, are considering similar solutions to the extraordinary cost of transporting the elderly and people with disabilities. A paratransit ride averages $29.30 in the United States, about three and a half times more expensive than the average cost of $8.15 to provide a regular fixed-route bus or rail trip, according to a report from the Government Accountability Office. In some cities, the cost is staggering: $57 in New York, and $50 in the District.

The Washington Metropolitan Area Transit Authority is planning to start a program in the spring to transition thousands of paratransit trips to a less-costly option, such as Uber or Lyft to save up to $6 million annually. Metro has yet to name its partners, but Uber and Lyft top the list of potential providers for what would be an alternative to MetroAccess, the agency’s door-to-door transportation for the elderly and people with disabilities.

Metro may look to Boston as it refines the program.

MBTA riders will pay the first $2 of each trip, and the MBTA will cover up to an additional $13 of each fare. Anything over that amount will be billed to the rider. Customers will be able to access the service through the Uber and Lyft apps. Lyft will also provide access via telephone, while Uber is providing smartphones to some customers who don’t have access to the technology, officials said.

In a blog post, Uber Boston General Manager Chris Taylor called the partnership, “a significant step in improving our transportation ecosystem.”

He said, “We are honored to work with the MBTA to build innovative solution for riders across the Commonwealth.”

Only a small number of MBTA customers will test the service in the next year, but officials say they plan to expand to a greater share of The Ride’s passengers.

As part of the agreement, Uber and Lyft are training drivers in dealing with special-needs populations, service animals will be allow on trips, and a share of the cars should be wheelchair accessible, officials said. About 80 percent of The Ride customers do not require accessible vehicles, officials said.

“Paratransit customers want to be treated in the exact same way as every other customer. They want the same access, the same mobility,” said Ben Schutzman, of the MBTA.  “This pilot could be the long way to providing that.”

Massachusetts Gov. Charlie Baker (R), who joined transportation officials and disability advocates for the official launch Friday, said the program will expand much-needed options for riders and offer them more efficient ways to get around. Disability advocates welcomed the program, saying it is a major step toward providing the kind of flexibility, responsiveness and on-demand services that riders with special needs deserve.

“Independent, reliable transportation is critical for people with disabilities to get to work, school or other community activities on time,” said Dave Power, president and chief executive of Perkins School for the Blind. “Paratransit riders can now access the same on-demand services enjoyed by people without disabilities – bringing us another step closer to inclusive public transportation.”