To cross the Delaware River, fewer commuters are driving and more are taking the train.

PATCO rail ridership reached an 11-year high last year, while vehicle traffic fell to an 11-year low on the four toll bridges operated by the Delaware River Port Authority.

Higher bridge tolls, rising gasoline prices, and a depressed economy all helped account for the shift, transportation experts said.

The increase in mass transit use also has been felt by SEPTA, where ridership is at its highest since 1989.

Last year, PATCO trains carried 10.5 million passengers between South Jersey and Philadelphia, the most since 2000, despite a 10 percent fare increase last year.

Meanwhile, vehicle traffic dropped to the lowest level in 11 years on DRPA bridges. Last year, 48.9 million vehicles went through the toll plazas on the Ben Franklin, Walt Whitman, Betsy Ross, and Commodore Barry Bridges, down from 50.4 million in 2010 and off the all-time high of 55.1 million in 2007.

Bridge traffic had been rising each year since 2000 until tolls were increased from $1 for cars in September 2008 to $4.

Tolls rose again July 1, to $5.

DRPA chief executive officer John Matheussen said the toll increases were partly responsible for the decrease in bridge traffic, but he said rising gasoline prices, and higher parking and insurance costs were also factors.

And he said younger commuters seem more amenable to taking transit instead of driving.

PATCO trains are increasingly popular for recreational trips, too, he said.

"It's not just work . . . people are going to events in Philadelphia, shopping, eating, going to sports events, and using PATCO to get there," he said.

PATCO's busiest year since opening in 1969 was the bicentennial year of 1976, when ridership reached 11.5 million. PATCO ridership has not been over 11 million since 1994.

"The recent toll hikes are driving motorists away from the DRPA's bridges," said Jenny Robinson, spokeswoman for the AAA Mid-Atlantic motor club. "In these tough times with many people still struggling financially, $5 is a lot to pay, and it's especially frustrating that the Port Authority has spent so much of the public's money on its economic development program, which AAA Mid-Atlantic has opposed."

Robinson said it was unfortunate that the DRPA "was not able to use its unspent development funds to reduce the toll hikes and maintain the DRPA's bridges."

Tony DeSantis, president of the Delaware Valley Association of Rail Passengers, said commuters were turning to PATCO and the Tacony-Palmyra Bridge, operated by the Burlington County Bridge Commission because of the higher bridge tolls.

"It's $2 to use the Burlington County bridges and $5 to use the DRPA bridges," he said. "It's cheaper to use PATCO or the alternative."

Matheussen said early indications were that last year's trends would continue in 2012. He said January's PATCO numbers were up from a year earlier, while bridge traffic appears to be "flat, if not slightly depressed."

Contact staff writer Paul Nussbaum at 215-854-4587 or pnussbaum@phillynews.com.