Beginning in October, the Brunswick Explorer bus service will have to raise an additional $40,000 in local matching funds to keep the wheels on the buses turning round and round.

Ridership has increased more than 75 percent since 2010, according to Lee Karker, executive director of Coastal Trans, the Rocklandbased company that operates the local bus service. But federal economic stimulus funds — which paid for 84 percent of the bus route’s operations expenses during that same period — are set to expire, leaving the service to come up with $90,000 in local contributions rather than $50,000.

Funding originally came from the federal government as part of its Congestion Mitigation and Air Quality Improvement program, which paid 80 percent of the Brunswick Explorer’s administrative costs and 50 percent of its operating expenses.

But after three years, the funding lapses into a Rural Transportation Subsidy, which dropped its funding to only 50 percent, leaving the service to ask its six benefactors — Brunswick, Bowdoin College, Brunswick Housing Authority, Mid Coast Hospital, Sweetser and United Way of Midcoast Maine — to make up the difference.

The town’s share is set to increase by $3,500, from $16,500 to $20,000. Other potential new resources are on the list for funding requests, too, Karker said.

“We have raised about half of the increase so far, but we’ve still got a ways to go,” Karker said.

“We expect to have some matching funds left over at the end of the year that we can aply to it, and we’ll find the rest from somewhere, somehow. I can’t see us not running the bus after September. It’s too important, and too many people rely on it.”

About 17,000 people rode the buses in 2010; since then, ridership increased by 50 percent in 2011 and by another 25 percent last year. The most recent figures available put 2013’s use rates at about 33,000 for the year.

Two buses run in a circuit Monday through Friday, from 7 a.m. until 7 p.m., and they currently average about 120 riders each day.

Lincoln Street resident Greg Barlag rides the bus about three times each week to get from People Plus to Shaw’s at Merrymeeting Plaza. Likewise, Darlene Mattocks, who lives in the Creekside Village senior housing development on Baribeau Drive, rides the bus daily.

Roseanna Rogers, too, is a frequent rider. She lives off Water Street and cannot drive anymore. Her illness limits her mobility and forces her to use a walker.

She rides the bus every day, sometimes for two or three trips.

“I go to Hannaford and to Mid Coast Hospital. I also take it to Wal-Mart to shop,” Rogers said. “It’s not far from town, but when you have a walker you need some help, and (it’s) nice to have the bus. My friends and family all work, so it makes it hard to hook up with them for a ride.”

The bus fare is $1.

“You can’t beat that,” Rogers added. “A taxi costs me $8 or $10 one-way, and on a fixed income I can’t afford that very often.”