Many details of the proposals remain to be determined, including the specific routes at either end of the transit line. MARTA will seek public input in the months ahead before filling in some of the details and choosing a preferred option early next year.

MARTA Deputy General Manager Josh Rowan said either bus rapid transit or light rail would benefit the region as it adds millions of people in the decades ahead.

“This is a great project,” Rowan said. “We don’t want to get overfocused on (transit) mode. It’s about moving people and shifting people out of vehicles.”

The Clifton Corridor proposals are the latest evidence that MARTA is in expansion mode for the first time in two decades. That expansion was made possible when voters in Clayton County approved a new transit sales tax in 2014, with Atlanta voters following suit two years later.

In Atlanta, MARTA is moving forward with a rapid bus line along Hank Aaron Drive/Capitol Avenue and along Campbellton Road. It also plans to extend the Atlanta Streetcar east to the Beltline and Ponce City Market.

The Clifton Corridor line would be the next major project. It would connect Emory and the U.S. Centers for Disease Control and Prevention to MARTA’s existing rail network.

MARTA has long planned to build a rail line along the corridor. But that plan has been thwarted by the reluctance of the CSX railroad to allow passenger rail along its right of way in the area.

But the railroad has recently had a change of heart, and MARTA plans to build the new transit line mostly in the CSX right of way. That would make construction easier and less expensive.

But MARTA is also reconsidering its plans for rail along the corridor. The agency has embraced bus rapid transit as a cheaper alternative to rail.

Though it does not yet exist in metro Atlanta, bus rapid transit is proliferating across the United States. It’s designed to mimic rail lines — passengers board at stations, pay in advance and get real-time information on arrivals. Rapid bus lines also operate mostly in exclusive lanes, which means they travel much faster than regular local bus routes.

In July MARTA said it would take 20 to 30 minutes for rapid buses to travel the Clifton route, compared with 15 to 26 minutes for rail. But bus rapid transit would cost substantially less than rail (up to $860 million vs. up to $3.1 billion), and it could be built faster (five to seven years, compared with eight to 10 years).

Last summer MARTA unveiled 10 possible combinations of routes and transit types for the Clifton Corridor. On Tuesday, it narrowed the options to three.

Two of the remaining options are bus rapid transit. Both would connect Lindbergh to Avondale, though one would add an “arterial rapid transit” route to Decatur. MARTA Project Manager Bryan Hobbs said the Decatur spur would operate in regular traffic on Clairemont Avenue, but it would still be faster and offer more amenities than regular bus service.

The light rail line would connect Lindbergh to Avondale.

Hobbs said extending the main transit line to Avondale instead of Decatur made sense because of residents’ concerns about traffic on Clairemont, the loss of trees and other impacts of the Decatur route. He said an arterial rapid transit line would have fewer impacts but would still provide enhanced transit service to Decatur.

MARTA wants feedback on its three proposed options. After making a final selection, it will begin more detailed design work and eventually apply for federal funding.

If all goes well, the line could open as soon as 2036.

MARTA’s Clifton Corridor

MARTA will discuss its plans for the Clifton Corridor transit line at 6:30 p.m. Thursday on Zoom: https://tinyurl.com/43yst32n. Dial-in Number: 301-715-8592. Meeting ID: 835 3599 3231. Passcode: 074658.