SEPTA changed its railroad ticketing policy this week to counter people gaming the system to get cheaper rides, the transit authority reported.

Tickets for passengers leaving Temple, Jefferson, Suburban, 30th Street and University City stations during the evening rush hours will be checked before passengers get to the platforms, as happens now, but the riders are getting those tickets back, and they are being checked again by conductors, SEPTA reported. The change went into effect Monday.

Last August, SEPTA shifted evening ticket checking from conductors to workers stationed above the platforms at the Center City stops to cope with a serious railcar failure last summer. Freeing conductors from checking tickets allowed them to board and clear trains more quickly, but it also allowed passengers to get on trains with the cheapest possible tickets and ride unchecked into more expensive travel zones.

SEPTA is not certain how much revenue was lost due to the ticketing policy, said Carla Showell-Lee, an authority spokeswoman. Estimating is difficult because SEPTA's services have had disruptions in the last year, most significant being the failure of a third of its rail fleet last summer and a strike on the city transit lines in November.

"We suspect that many commuters may have changed their method of travel to save money," Showell-Lee said.

The authority anticipated having a better idea of the revenue loss at the end of July.

The Delaware Valley Association of Rail Passengers, an advocacy group, has lobbied SEPTA to adjust its ticketing policy to make it harder for people to evade fares or underpay for rides. This week's change will bring in more revenue, said Matt Mitchell, the organization's vice president.

"They're going to temporarily, at least, reduce the shrinkage," he said.

This solution may be temporary, though, because SEPTA's smart-fare card, SEPTA Key, is expected to be introduced to the Regional Rail, the 13 train routes that link Philadelphia to its surrounding communities for about 65,000 daily riders. That transition is expected to happen this fall, SEPTA has said, and Showell-Lee called it "a game changer."

Riders will be able to tap card readers at platforms with their cards when they board and depart trains in the suburbs, and will have to pass through turnstiles at the Center City stations when they get on or off trains there.

Rail experts, though, are concerned that Key cards will bring new headaches. The Key card system will automatically charge a rider the highest fare if the person fails to tap the card when getting off a train, said rail expert Michael Noda, who has blogged about SEPTA's fare collection, preventing the kind of gaming SEPTA is now facing. SEPTA's decision to not install fare card machines at all its stops, something the authority says is cost prohibitive, will mean conductors could continue to be in the business of checking and selling fares, potentially creating delays and opportunities to hitch a free ride for those not getting on or off in Center City, roughly 5 percent of the Regional Rail's ridership.

"It's very hard to strictly enforce intermediate fares going from an outer station to an outer station," Noda said. "It's going to be really hard for the conductors to intercept everybody who's getting on at a non-Center City station."