The three-month pilot program beginning Wednesday will waive the $2 fare on the Massachusetts Bay Transportation Authority's Silver Line buses that take passengers from the airport, the 19th busiest in the U.S., to South Station in central Boston.

"Logan has tried various ways to curb parking demand and wean passengers from driving to the airport," said David Mackey, interim chief executive officer of Massport, the state agency that operates the airport. "Logan cannot build new garages to meet demand."

The airport, located on a marshy spit of land across Boston Harbor from downtown Boston, has seen annual passenger traffic rise from 15.1 million in 1980 to 28.9 million last year. The airport is barred from building new parking garages by environmental laws.

In March, transport officials raised airport parking fees to as much as $27 per day while cutting fees to $7 a day at suburban lots that provide direct bus service to the airport as part of the effort to cut car trips to Logan.

"We don't know of any other place where you can travel for free on the transit system coming from the airport to downtown," said Virginia Miller, a spokeswoman for the American Public Transportation Association.

(Reporting by Jason McLure; editing by Carol Bishopric and Sandra Maler)

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