Thousands of people lined up for up to three hours or more in Toronto on Monday to take a train that normally struggles to fill more than 10 per cent of its seats: the Union Pearson Express (UPX).

They took advantage of the opportunity to ride the train for free on Family Day weekend, courtesy of Metrolinx. And according to the regional transit agency, many of them said they're doing it just to try it out.

Metrolinx spokesperson Anne-Marie Aikins told CBC News that Metrolinx made the move to show people how easy the train is to get to and how quick it is to make the trip between Union Station and Pearson airport, and she said Torontonians have responding in record numbers. 

"We have more than met our goal. We couldn't be more excited about the number of people that have come out," Aikins said.

However, while it was a free-for-all on the UPX, Metrolinx officials ensured that travellers actually trying to catch a flight at Pearson Airport were given priority. 

Aikins said the line at Union Station for people trying out the train was about a three-hour wait, but there is no wait for those with a flight or for airport staff.

The free rides began Saturday, and Metrolinx said more than 10,000 people rode the train that day. Aikins estimated that as many as 15,000 people had taken the train on Monday by the middle of the afternoon. ​

Aikins acknowledged that the main reason the numbers were so high was because the service was free. 

Ridership for the UPX has been very low since it opened last year with most trains operating 90 per cent empty.

One of the main issues with the service has been the price: it costs $27.50 for a one-way adult ticket, and $19 with a Presto fare card.

Emily Jane, one of the passengers who waited hours in line to take the train with her young family, told CBC News $27.50 is too steep a price for her.

"A $10 price range is a bit more reasonable, I think." she said. 

"I think it's a great concept, I really do, and it's long overdue," said Gerald Silveri, who had also been waiting for two hours to get on the UPX. "But it's too expensive ... I think I should be able to get on it with my Metropass."

Last week, after a meeting of the Metrolinx board, Transportation Minister Del Duca said the province would take a 'real, hard look' at UPX fares. 

"We have been hearing that people would prefer a much more accessible price," Aikins told CBC News.

"We are taking that very seriously and putting our heads down and developing a new strategy that will come out in the next couple of weeks."