If the Cardinal and Hoosier State were split, I would imagine the Cardinal's daily ridership would plummet without passengers traveling between CHI-IND only.
You are dead wrong, PhillyAmtrakFan, because you haven't analyzed the way the market for train service actually works.
When you have *two* daily trains, as long as they're on substantially different schedules and both in the daytime, people take one out and the other back.
A daily Hoosier State on a schedule to leave IND in the morning and arrive IND in the evening would BENEFIT the Cardinal (which leaves IND in the evening and arrives in the morning). If the schedules were tweaked appropriately and made somewhat faster, people would take one train out and the other train back.
Make the Cardinal daily (by itself), you get 7/3 as much ridership, minimum: that's 2.3 times as much. This isn't disputable, this change is documented from previous 'experiments' Amtrak has done; it's usually more than that..
Then add a Hoosier State on the 'opposite' schedule from Indianapolis to Chicago. Joint Hoosier State-Cardinal ridership on the Indianapolis-Chicago corridor would likely be 2x as high as for one train a day, meaning that the Cardinal would have the same number of riders. Even if ridership was only 1.5 times as high for two trains a day as for one train a day (and this is the minimum improvement which has ever been seen when this change was made), that is only a reduction of 25% on the Cardinal's IND-CHI ridership (only), and that's relative to the new (2.3x as high) baseline.
Think about it. If there were a morning train and an evening train from Indianpolis to Chicago each way, the ridership on *both* trains benefits.
The benefits of a more frequent schedule are that they cause people to take the train who would not have considered it because of scheduling. Going from less-than-daily to daily adds a huge number of potential passengers, and going from daily to twice-daily adds a very large number of potential passengers. Going to higher frequencies continues to add more passengers, though the returns diminish.
Another way to look at this: a daily Cardinal will mean 7/3 as much ridership on the IND-NYP section, while a twice-daily Cardinal and Hoosier State will mean 1.5x-2x as much ridership on the shared IND-CHI section. Costs increase by one trainset for the Cardinal, and none at all (more hours but no more trainsets) for the Hoosier State. This is a win-win.