This is an issue only for the Luddites. For the rest who use their Smartphone to buy and display tickets, one buys the appropriate ticket just before boarding the train. I can't remember the last time I used a paper ticket on any of the NY area Commuter Services.
CHI-MKE service is Amtrak service with ticketing available through the Amtrak App, so just buy the ticket just before boarding the train.
So, here's the scenario I have in mind....
One travels to Milwaukee (or Chicago) for a day trip, expecting to return that evening. For ease, you purchase a return ticket (let's say it's an eticket, off your phone) at the same time, on your expected train. But, you stay in town late...maybe even overnight, skipping the original booking. So, you don't bother to cancel and rebook. After all, you already have a good ticket in pdf. Just use it on whatever train you do take home. But, if you paid a couple bucks more for the rush hour return, or if the next train is peak service and your ticket wasn't....
Obviously, the easy answer is "Cancel and rebook." But, what if one doesn't think to do so, and simply boards? Now what?
As a practical matter, I'm considering organizing a group trip upon which travelers may wish to return at different times, depending on whether they are interested in getting home faster or spending some time in Milwaukee. The easiest thing to do would be to offer them each a personal ticket for the next trip back to Chicago, note the return trip times, and let them choose, individually, to get on whatever train they want. Some (most) are likely unfamiliar with Amtrak procedures, however, so it isn't as straightforward as it might be for a regular commuter.
