Offering free fares on Utah Transit Authority routes on the Friday before Christmas packed trains with an estimated 23,000 extra passengers — but bus ridership stayed flat.

But UTA spokesman Carl Arky says it all depends on how one looks at it.

He says bus ridership usually falls by about 5 percent on the last workday before Christmas, as many people take off to shop or stay home instead.

Because bus ridership remained essentially the same, “it’s like having a 5 percent increase.” He added, “As I drove around a bit that day, the freeways were pretty empty. A lot of normal commuters took that day off.”

The agency said the single-day ridership on FrontRunner commuter trains was up by 66 percent for a total of 30,016 boardings. (A boarding is anytime someone enters a train — and a single trip may have several boardings depending on transfers).

Ridership on the TRAX light rail was up by 32 percent, for a total of 79,825 boardings.

Bus ridership increased by only 278 boardings, Arky said, for less than a 1 percent increase for its total of 61,735 boardings that day.

Overall on all trains, buses and streetcars, UTA figures ridership increased by 31,732 boardings — up 23 percent compared with the average of the five preceding weekdays. It estimated that translated into an extra 22,829 riders that day.

The agency figures that removed 17,560 cars from the road that day, preventing 3 tons of pollutants and 200 tons of greenhouse gases.

The Salt Lake City Council, the Salt Lake County mayor’s office and UTA teamed up to offer the free-fare day by chipping in the $70,000 that covers the average weekday take on cash fares.

“It’s encouraging to see that so many people embraced Free Fare Friday,” said former Salt Lake City Council Chairman Stan Penfold, who led efforts to sponsor the event.

He said that shows residents “will respond positively to common-sense ideas that make a difference on the big issues we all care deeply about, like improving our poor air quality.” He adds that it may help motivate continuing exploration of “innovative approaches that can clean our air and increase transit ridership.”

But UTA said in a news release that only limited opportunity exists for more free-fare days.

It said, for example, offering free fares on all poor air-quality days “isn’t feasible, as UTA requires fare revenue to operate.” Also, the agency said the system has limited capacity “and can’t accommodate thousands of extra riders when universities are in session.”

Still, UTA said it “will continue to look for innovative ways to encourage public-transit use and improve air quality.”

County Mayor Ben McAdams said, “Free Fare Friday was a fun and easy way for me and my family to get better acquainted with public transportation options. … We can all do our part to help clean the air and when we do — based on this promotion — the improvement is significant.”

City Creek Center General Manager Linda Wardell said the free fares seemed to help her mall.

“The size of the crowds streaming off TRAX trains and into the center throughout the day and evening were amazing. Shops were packed and some of our restaurants stayed open late to serve hungry shoppers and visitors,” she said.