AFTER GOING NEARLY five decades without making any major changes to the MBTA’s bus route system, the transit authority on Monday unveiled a preliminary redesign that is expected to provide more service at greater frequency on more routes.

The new system, after going through a public review and some possible tweaking over the remainder of this year, will start phasing in next spring or summer and be fully operational five years later. The extra cost of the expansion at full buildout is expected to be $90 million a year.

Steve Poftak, the T’s general manager, said the Boston area has changed dramatically over the last several decades but the bus network has not changed with it. He said the changes being put forward are long overdue.

The routes with frequent service, defined as pickups at least every 15 minutes all day every day of the week, are doubling from 15 to 30. Several communities, including Everett, Lynn, Medford, Somerville, South Boston, and West Roxbury, will see a sharp uptick in frequent service.

The Longwood Medical Area is being given very high priority, going from two to six routes with frequent service. Everett will go from one to four, Lynn from none to two, and the Roxbury neighborhood from six to nine.

In all, Poftak said, the redesign will increase service 25 percent across the entire network and 70 percent on weekends. He said an estimated 275,000 more residents in the MBTA service area will now have access to frequent service.

The T is facing what many are calling a budget cliff in fiscal 2024, which begins in July 2023, but Poftak said the money needed for the bus redesign is already programmed into the T’s spending plans. He indicated that, if spending cuts are necessary, they will be found in other areas.

“This is the MBTA our riders, particularly our bus riders, are entitled to,” Poftak said.

The general manager acknowledged that providing the service won’t be easy, given problems in hiring enough bus drivers. He said the number of dropped trips on the system has been increasing recently, but a top aide corrected him to say dropped trips are down slightly, from 5 percent at the beginning of the year to somewhere between 2.5 percent and 5 percent now.

“We have gotten better since Omicron,” said Kat Benesh, chief of operations strategy, policy, and oversight.

At a press conference at the state Transportation Building, Sen. William Brownsberger of Belmont praised the T for pushing ahead with a redesign when most government agencies are loathe to change anything to avoid pushback.

“This is the kind of project that can get torn apart by politics,” he said.

Rep. Russell Holmes of Boston said he would like to see the redesign move more quickly. “I am tired of studying this,” he said.

Poftak acknowledged there were tradeoffs when redesigning the bus system, but he was vague about what those tradeoffs would be, other than to say some communities would see reduced access to the bus system and less frequency. Transportation Secretary Jamey Tesler said “the plan puts equity first.”

Stacy Thompson, executive director of the Livable Streets Alliance, said she loved the redesign and said it’s up to Beacon Hill to make sure the T is able to afford this expansion.

“It’s up to the Legislature to make sure we are not dancing on a fiscal cliff,” she said.

To read the MBTA’s materials on bus redesign, click here and here.