LAWRENCE, Mass. — Dionisia Ramos gets on the 37 bus twice a day, rooting through her handbag to dig out the fare and drop it into the slot, so it came as a shock several months ago when the bus driver reached out his hand to stop her.

“You don’t have to pay,” he said. “It’s free for the next two years.”

Ms. Ramos had never heard of anything like this: Someone was paying her bus fare? At 55, she lives on a monthly unemployment check for $235. So saving $2.40 a day, for her trip to and from community college, past the hulking mills of Lawrence’s industrial past — that meant something.

Since a pilot program began in September, use of the buses has grown by 24 percent, and the only criticism Ms. Ramos has of the Massachusetts city’s experiment with fare-free transit is that it is not permanent.