(CBS) — CTA bus ridership is down and the transit agency is offering a lot of reasons why.

CTA, Metra and Pace all say the polar vortex drove away riders for much of the winter. But CTA Vice President/Finance Tom McKone said a variety of other reasons contributed to the 3.1 percent year-to-date decrease — the drop in the price of gas, slower traffic on city streets, the emergence of the Uber and Lyft ride-sharing services, last year’s free Red Line South construction bus shuttles and reduced-fare South Side CTA bus service, and a decrease by 10 in the number of school days, because of days made up in the spring of 2013 because of the 2012 teachers’ strike.

“We know that on school days we actually experience quite a bit more ridership than on non-school days,” he said.

McKone said CTA’s experience — including the clogged streets — is consistent with national trends, and that the agency sees a shift from bus to rail. Ridership on the ‘L’ has been up by more than 4 percent; in fact, he said rail ridership is expected to be the highest since modern CTA record keeping began in 1961.

Pace ridership has dipped so far this year by 1.2 percent.

While CTA and Pace expect that trend to reverse itself, with modest gains in 2015, Metra expects a temporary 1 percent dip when its fares increase in February. But Metra Chief Financial Officer Tom Farmer said that after a few months, the riders always come back.