PORTLAND — The Zoom commuter bus, which connects Portland with Biddeford and Saco, should increase service and expand to Kennebunk, Wells, Lewiston-Auburn and Augusta, advocates for alternative transportation said today.

The Maine Turnpike Authority, which helps to fund Zoom through a $115,000-a-year matching subsidy, should contribute $7 million from toll revenue to make it happen, they said.

The proposals are in a report, “A Turnpike for the 21st Century,” prepared by the Maine Alliance for Sustainable Transportation. Its goals include taking cars off the road, helping workers get to jobs and reducing the need for highway projects around Portland. They are part of a wider strategy by environmental and alternative transportation advocates to find ways to reduce traffic congestion, other than building new roads and widening existing ones.

The group plans to draft legislation for next year that it hopes will pressure the turnpike authority to share more of its revenue for expanded bus service.

“The turnpike authority should manage its infrastructure more efficiently, to make better use of the existing pavement,” said Christian MilNeil, a member of the alliance’s steering committee.

Expanding Zoom makes sense, MilNeil said, because it’s a successful service that has more than doubled ridership in the past five years and receives no state or local subsidies. Compared with passenger rail, it’s fairly quick and inexpensive to put more buses on the road, he said.

MilNeil said his group has had initial discussions with the staff of the turnpike authority, but the authority said Thursday that it disputes some of the alliance’s central conclusions.

Zoom ridership is down this year by 18 percent, said the turnpike authority, which has put off and scaled back plans to widen the highway through Portland. Also, it doesn’t have money to put toward expanding bus service, said Scott Tompkins, a turnpike authority spokesman.

“It’s not within our long-range budget,” said Tompkins. “We don’t have the money to subsidize them like that, and we don’t perceive the need.”

Zoom’s director, Al Schutz, said he just started his job and doesn’t have the background yet to comment.

Zoom is a 12-year-old express bus service. It now runs 10 daily trips on the Maine Turnpike between Biddeford and Portland. It leaves from turnpike park-and-ride lots. A one-way ticket costs $5; monthly cards cost $80.

According to turnpike authority figures, annual ridership peaked at 46,000 in 2008, a period of record gasoline prices.

The service costs more than $332,000 a year to operate. Fares and advertising cover about $97,000.

The services receives $110,000 a year in federal highway funds that flow through the Maine Department of Transportation. The turnpike authority contributes $115,000 a year. This year, it also contributed $60,000 in matching funds to help buy two new buses, Tompkins said.

The proposal by the Maine Alliance for Sustainable Transportation would add four new buses for a total of 30 round-trips, including 20 to downtown Biddeford-Saco, which would serve residents and business at newly renovated mills. Service also would expand to park-and-ride lots in Kennebunk and Wells.

The alliance also wants a rush-hour service to downtown Lewiston and Auburn, with 16 round-trips daily. That line would tap into development activity in Lewiston’s mill district.

The success of existing van pools between Portland and Augusta shows that demand exists for rush-hour commuter bus service to the capital, the alliance says.

The expansion of service would cost $7 million, to buy 10 new buses, improve bus stops and cover other expenses. Adding 86 hours a day to operations would cost an extra $2.6 million per year. That’s much less than the $150 million that the alliance says the turnpike authority has been planning to spend on the highway west of Portland.

But Tompkins said that’s a flawed comparison. The authority put off widening the highway from Scarborough to Falmouth last year, in the face of declining traffic projections. It has since cut back the scope of any project, and no work will be done before 2018.

“Widening is not on our radar,” Tompkins said.

He also questioned the need to expand bus service to Lewiston and Auburn when a pending Department of Transportation study of transit needs north of Portland has identified bus service to Bath-Brunswick as a higher priority.

MilNeil said census data indicates that there are enough residents and workers to make bus service between Lewiston-Auburn and Portland viable.