(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.

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

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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.

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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.