T ridership is at its highest rates since March 2020, when the coronavirus pandemic lockdowns began, thanks to a post-Labor Day boom in riders. But there have been some bumps in the road.

The T says the increase in riders is due in part to students and workers returning to work and classes in person.

“We're seeing the most recovery on the bus and the Blue Line, and then it decreases from there to the next highest is the Green Line, then the Red Line and then at the bottom of the barrel is the Orange Line,” said Chris Friend, a board member at Transit Matters whose work includes transit advocacy and analyzing transit data.

When Friend compared current ridership levels to their pre-pandemic counterparts, he found buses now have about 75% of the ridership they used to. The Blue Line is at about 70% its pre-pandemic ridership; Green Line just over the 60%; Red Line in the mid-50s and the Orange Line just over 40%.

The Orange Line’s low rebound is likely caused by the complete shutdown of the line for 30 days in August and September. Before the shutdown, Orange Line ridership levels were closer to pre-pandemic levels than the Red Line.

“When you have a month when you don't use it, I think a lot of people find a different way to travel,” Friend said. “I think these travel modes are sticky. Maybe you saw a lot of people who used to take the Orange Line and now take commuter rail or bike or drive or do something else.”

Ridership levels depend on who uses the line and how reliant they are on public transit.

“Part of it is definitely the transit dependency of the populations,” Friend said. “And I think we've seen this throughout the entire [COVID] shutdown, that the Blue Line and buses had higher ridership than the other lines because people who use them need them more, and don't have as many other options as people may ride the Orange Line or the Red Line.”

What's worth noting, Friend said, is that even on the Blue Line, which has retained ridership more than other lines, the number of people is still down significantly. He attributed that to the fact that earlier this year, the T cut service on the Blue, Red and Orange Lines because of staffing and safety issues that prompted a federal probe into the agency.

“The biggest thing right now, and I think the biggest thing you see people complain about, is the time between trains, or the headways and how long people have to sit in the station and wait,” Friend said. “I think as soon as possible, you've got to reverse those service cuts from the summer and bring those service levels back to and above what we were doing.”

Until services are bumped up, the T is probably not going to see ridership back at what it once was. But there's an interesting ripple to all of this, Friend said. The bus routes that have rebounded the most in ridership all saw either boosted service on the route, or were part of Boston’s fare-free pilot program. City officials used American Rescue Plan Act funds to make routes 23, 28 and 29, which travel through Mattapan, Dorchester and Roxbury, free to ride until 2024.

But for now, a free T across the board is just a pipe dream. The city of Boston doesn't have jurisdiction over the T and the T relies on fares for funding.