I don't think paying somebody to vote is a crime. Telling them to vote for a particular person is, though.
https://www.law.cornell.edu/uscode/text/18/597
As a sibling to your comment points out, the discount isn't in exchange for voting.
If voting is such a burden that offering discount on rides improves our voting turnout - sounds to me like that's fixing a problem as opposed to fixing an election.
Voting is key to the democratic process. The fact that one party prefers to tell people NOT to vote is more worrying to me than increasing turnout.