MBTA bus drivers will have their day in court next month in their bid to win what could be millions of dollars from the transit agency for the time they spend traveling between bus assignments.

In the federal lawsuit that is set to go to trial in January in U.S. District Court in Boston, 10 members of the Carmen’s Union Local 589 will argue they should have been paid for the time it took them to travel from the end of one bus assignment to another. MBTA bus drivers routinely work part of their shift driving one bus route, but switch to another route midway through their shift. That can often mean traveling from the end of one route to the beginning of another in a different part of the city.

Getting from route to route can take as long as 50 minutes, union lawyer Douglas Taylor said. Full-time employees who begin work at one location and then report to drive a different route the same day are paid for 20 minutes.

Last year, Judge Douglas Woodlock said case law is clear that required travel during a two-part shift should be paid. “Travel time during split shifts is compensable,” he wrote.

But Woodlock declined to rule on the individual plaintiffs’ claims, citing a need to see detailed work and travel records. During the trial, the plaintiffs will need to show exactly how often they traveled between routes and how long it took.

By law, damages must be awarded individually based on how much unpaid travel each driver took. To make the process more manageable, the judge ordered the cases to be separated, with several hundred drivers in each case.

The eventual payout could be in the millions, Taylor said, but he added there is no way to know for sure because the MBTA has so far refused to do required payroll and work database searches that would reveal the true amount of the unpaid travel. An MBTA spokesman declined to comment on the case.

MBTA bus drivers make more than $35 an hour, the highest hourly rate in the country.

“Nobody’s going to get rich over this,” Taylor said. “The union is much more concerned in making sure the T follows the law than we are in getting a lot of money.”

Recently, the T has taken aggressive cost-cutting steps, including privatizing the problem-plagued money room. Officials have also said they are considering outsourcing other parts of maintenance and operations, including bus drivers. The agency expects to have a $126 million deficit this fiscal year.