THE MBTA on Thursday unveiled a redesign of its initial redesign of its bus network, incorporating feedback from 20,000 commenters and changing 85 of the 133 routes in the original proposal.

Testifying before the MBTA board, T officials said the latest plan expands service by 25 percent and doubles from 15 to 30 the number of high-frequency routes, where buses will arrive every 15 minutes or less all day long every day of the week.

Officials say they expect the redesign will go before the MBTA board for final approval in December, but it will take five years for the program to be phased in.

The biggest challenge may be hiring enough bus drivers. T officials said they need 312 drivers to get back to previous pre- COVID service levels and 440 additional drivers to provide expanded service. The total of 752 new drivers represents a 50 percent increase above current levels, the officials said.

“It’s a really quite massive number, and that’s another one of the reasons that this is split out over multiple years, because hiring that volume of operators and all the other supporting positions just really takes a lot of time,” said Melissa Dullea, senior director of service planning.

The MBTA is trying to hire 2,000 new employees this year.

Cost is another concern. The T estimates the net operating cost (cost minus fare revenue collected) will rise from $20 million in the current fiscal year to $119 million in fiscal 2025.

There are also significant capital costs needed for new bus stops and road reconfigurations, and many transportation advocates say bus redesign won’t truly be effective until far more routes operate using bus-only lanes, which require cooperation from local municipal officials.

Betsy Taylor, the chair of the MBTA board, said the program shows great promise but a lot more work is needed to identify the revenues to support it. “To make it real, we need to be able to afford the capital and operating costs,” she said.

Doug Johnson, the bus redesign project director, said the goal all along has been to expand service and cater more to riders who are dependent on transit for getting around. COVID also had an impact, prompting a shift away from service at peak travel times toward more service throughout the day.

For example, the SL2 bus, which runs from South Station to the World Trade Center and from there on to Drydock Avenue, has been focused on service during peak commute periods Monday through Friday. After consultation with community members, Johnson said, the SL2 will now operate all day long seven days a week.

The service every 15 minutes or less on high-frequency routes was designed to give riders more confidence about boarding a bus quickly. “We want the service to be frequent enough so people don’t have to check schedules,” Johnson said.

The original bus redesign came out in May and then T officials spent time gathering feedback. Based on the feedback, the officials said, two-thirds of the proposed bus routes were changed. Some involved minor changes, to bring the route closer to a hospital, senior center, or grocery store. Other stops were relocated to reduce walking times to the bus or help seniors navigate difficult terrain.

A number of proposed routes were simply scrapped, and the original route restored. Eleven residents of the Keystone Apartment building in Dorchester called in to the board meeting, urging directors to bring back Routes 201 and 202. One resident, Carol Murphy, said scrapping those routes would leave residents stranded. “It’s a disgrace,” she said.

In his presentation, Johnson said the 201 and 202 routes won’t be changed. He said Routes 29, 39, 55, 354, and 505 will also remain unchanged, along with a number of others. (Check new route map here.)