You'd be forgiven if you didn't know that the Massachusetts Bay Transportation Authority was undertaking an experiment.

The operator of the MBTA's commuter rail, Keolis, is offering a new discounted weekend fare that it hopes will drastically increase ridership.

"We're looking to test to see if we can can get more riders on weekend trains by lowering the price. So it's 10 dollars to ride the commuter rail all day on Saturdays and Sundays," said Keolis Public Affairs Director Tory Mazzola. "[And] children 11 and under are free, so for a family this is a really affordable option to go in and out of Boston or go around the community see all that we have to offer."

Mazzola said there has been a comprehensive marketing campaign for the summer weekend fare, but a visitor to South Station would have no idea the summer fare existed. There aren't signs or advertisements anywhere.

And in a random sampling of passengers at the Attleboro commuter rail stop, riders like Ashley Carter and Raphael Nunez of Attleboro hadn't heard of it at all.

Passengers in Attleboro who were using the reduced ticket fare didn't find out about it through media. Passenger Nick O'Brien said his friend told him about it ... but he doesn't know how his friend knew. And passenger Brian Mixta said the conductor on board his train told him about it, and gave him a discount when he paid his usual Saturday fare. But he hadn't seen or heard any publicity about it either.

Tory Mazzola said Keolis isn't targeting those riders.

"Our main audience is new riders," he said, "which is why our digital marketing and other advertising, including direct mail and other channels, focus on people throughout the greater Boston area planning to go to events, see shows, etc. — people who don’t typically think of commuter rail as a transit option."

Mazzola maintained that the folks I met in Attleboro are likely already regular riders, who will, as was the case with Brian Mixta, learn about the fare from a conductor. "To give you an example, many of our weekday riders are monthly pass holders, which they buy for work on weekdays, and this pass includes weekend travel," he said.

And although I didn't see any evidence of them either at South Station or in Attleboro, Mazzola said, "our marketing and advertising program includes in-station signs [the digital boards/monitors the MBTA operates.] Our crews make in-station and on-board announcements. We’ve also had MBTA and Keolis staff at the major stations during the launch of the program, handing out flyers to promote the service during mid-week rush hour."

Since the special summer weekend fare has only been offered for one month, Mazzola said, it's premature to know how much ridership is increasing, if at all. But those who have taken advantage of the weekend fare, like Chris Dempsey who runs the advocacy group Transportation for Massachusetts, thinks it's a great idea.

"I went up to the North Shore, and went to Ipswich, to Cranes beach, then I had a beer at the Ipswich Brewery, and just had a great opportunity to explore a part of the state I don't get to enough," Dempsey said. "And that only happened because of that discounted fare; that's the only reason I made the trip."

While I couldn't find any publicity about the weekend commuter rail fares, posters advertising the Cape Flyer weekend service to Cape Cod were prominently displayed in South Station. Cape Cod Regional Transit Administrator Tom Cahir said marketing — especially using social media to attract visitors to special events — has been a key factor in that train line's success over the past six years.

"We monitor how many likes we get for various things," he said, "and I think it's contributed greatly to the success we've enjoyed."

That success sees the Cape Flyer turn a profit every year, steadily growing its ridership by about 3 percent annually. It now carries 15,000 passengers per season. Cahir says it takes time and intensive promotion to make the service work.

Tory Mazzola said that this is the first time Keolis has tried a pilot program on this scale, and he admitted there is always something to learn. Since what happens with this summer's weekend fare could set a precedent for future reduced fare service, getting as many people as possible to ride this summer might be critical.