This fall Metro will officially open the bidding process for contractors to provide paratransit services, providing an alternative to MetroAccess, its door-to-door service for the elderly and people with disabilities.

The popular ride-hailing companies Uber and Lyft top the list of prospective contractors for the new service, which officials say could help the transit agency save millions on its heavily subsidized paratransit program. It also would answer customers’ growing demand for same-day, app-based transportation services.

Metro plans to issue an RFP in September with the intent to have the service in place by spring 2017, according to Christian Kent, assistant general manager for Metro’s Access Services department. The pilot program will be for users in the Maryland suburbs, where two-thirds of MetroAccess customers live.

Officials anticipate the option will be popular among customers who don’t need wheelchair-accessible vehicles to travel. Under the program, they will have the choice of booking a ride on the same day they need it, a significant improvement from the current MetroAccess requirement that trips be booked 24 hours in advance.

Concerns have been raised, however, about Metro’s intent to partner with companies like Uber to transport people with special needs. Advocates cite Uber’s lack of ­wheelchair-accessible vehicles and question the level of training its drivers receive in dealing with people with disabilities. They also echo concerns about safety, insurance coverage and the vetting process for the companies drivers.

In a letter to the Metro board, the panel’s Accessibility Advisory Committee this week urged Metro to set safety and security standards for the program, to be open to contracting with local transportation providers instead, and to keep in mind that many elderly and disabled customers cannot navigate web-based applications because of their disabilities.

But the group also said it supports Metro’s objective to sustain the costly MetroAccess service, acknowledging that a new program could help lower costs. A paratransit ride averages about $50 in the Washington area, a much higher cost than using rail or bus, which average between $3 and $4.

In an effort to bring down cost of paratransit services, transit agencies across the country are pursuing partnerships with app-based transportation providers.  Metro officials have said that expanding options and lowering costs are inevitable as demand for service increases with the population continuing to age and disability rates on the rise.

“We are trying to leverage a network that is more pervasive in the community than just a couple of cab companies,” Kent told a group of advocates at an Accessibility Advisory Committee meeting on Monday. “You have asked us to get creative, you have asked us to find ways to serve the community better and you are starting to see us trying new things.”

It is unclear what Metro will be seeking from bidders, but some officials say it may not be much different from an informal request for proposals issued earlier this year in which the transit authority said it was looking for service providers that can connect customers to drivers via an online platform, a system that mirrors Uber’s.

The agency said then that it would pay up to $15 per trip to the contracting company and cover a $12 surcharge applied to trips in wheelchair-accessible vehicles. Customers would be restricted to four trips daily.

Metro has also said it will ask the chosen provider to facilitate the reservation process through a traditional phone call. And it may ask the companies to spell out their policies for vetting drivers and training them to serve people with disabilities. Officials have also said they would want the service to be available to customers traveling with service animals, and to have at least 50 wheelchair-accessible vehicles to compliment the service.

The AAC also urged Metro not to set restrictions on the number of trips customers will be able to take.

“People with disabilities are interested in having the same level of access and quality of life as the non-disabled peers. A limit on trips will diminish that option,” the letter said.

The group asked that “any alternative service must be fully compliant with the [Americans with Disabilities Act],” a request more difficult to meet given that most transportation companies don’t have ADA accessible vehicles.

MetroAccess provides about 2 million trips annually at a price of about $121 million, of which more than 90 percent is paid with local subsidies. Metro projects the service could add at least a million trips and more than $50 million in operating expenses in the next decade. Partnering with other transportation services, however, could potentially lower costs by half.