The MTA can help passengers get to and from LaGuardia Airport more efficiently without costing straphangers by creating a free shuttle bus service, a transportation advocacy group said Monday.

The Riders Alliance released a report saying only 12.5% of the airport travelers use public transportation, even with several bus options including the Q70, which stops at the terminals, the Woodside LIRR station and the Jackson Heights, Roosevelt Ave./74th Street Broadway subway stations on the No. 7 line.

John Raskin, the nonprofit's executive director, said about 80% of that Q70's riders transfer from the subway, and thus don't contribute any revenue to the MTA. The group proposed that the Q70 become the free shuttle bus instead.

"You shouldn't have to memorize the Queens Bus map to get to LaGuardia," Raskin said at a news conference outside MTA headquarters.

The report, which surveyed 700 Q70 riders and analyzed Port Authority statistics, said the shuttle bus would bring an additional 213,000 LaGuardia travelers to public transportation. It has the support of the Global Gateway Alliance, an airport advocacy group, the Regional Plan Association and the Straphangers Campaign.

The MTA, however, wasn't too keen on the proposal. The agency's spokesman, Kevin Ortiz, said that if ridership were to grow on the bus line, they'd have to add more service which would raise costs.

"At the end of the day, there is simply zero evidence that making it a free shuttle would increase ridership on subways to the point it would make the shuttle self-sustaining," he said in a statement.