I had occasion to ride the Red Line a couple of months ago and encountered a few of annoyances. The first was that the ticket machine didn't give real change. Instead, it gave me some kind of "Change Ticket" that I could use towards the purchase of future fares, except that it expired in like a week or two, well before I'd have a chance to use it again.
I boarded the train in the front car, but the blaring safety horn was loud and nerve-wracking. So when the train stopped I moved to the rear car, but then I was overcome with the stench of diesel. There are only two cars, so you have to put up with the blaring horn or the horrible diesel smell.
I had a better experience on trains in India.
I found it, it's an "Electronic Change Card", good for only 15 days after issue, and usable only at ticket vending machines (not on the bus), non-transferrable, and non-redeemable, even at the CapMetro office.
I guess I was spoiled by my time in Los Angeles, where the ticket machines give actual change.