TRAX ticket-vending machines are moody.
With a smooth technique and a bit of finesse, you can often induce one to accept dollar bills in exchange for a $2 one-way adult fare. If the machine doesn’t like your looks, however, it rejects your currency with dismissive alacrity and, if you don’t leave it alone, it confiscates your lunch money and goes into Sulk Mode. At that point, there’s nothing any layperson can do; only a member of the orange-vested priesthood caste knows the proper incantations and supplications required to restore its good graces.
Some riders have discovered UTA’s magical tokens, which not only almost always work, but can be purchased in bulk at discount prices. Starting Sept. 1, however, TRAX machines will no longer accept these. (Turns out, unscrupulous riders in Sandy have discovered the machines work just fine with cheap arcade tokens—better, apparently, than with actual money—and have been stealing $10,000/month in fares.)
Pocket change still greatly pleases the ticket-machine gods, as long as you drop coins in very slowly. So be sure and show up in plenty of time, and be prepared to jingle merrily throughout the day.