Are you talking about Chicago? An express train sounds great, they should absolutely build one, but I think you're being a little harsh on the existing train. By America's (very low) standards it is quite convenient. It is already much faster and cheaper than driving, I have never even considered taking an Uber and I'm not sure it would be worth paying much more for an express train.
Correct, Chicago. The city's even already bored the station downtown as part of another project, so there's a massive underground cavern in the middle of downtown currently going unused.
The last time I took the Blue Line to the airport it was indeed fast and convenient - but dealing with luggage was kind of annoying, and there was a guy smoking weed on the train. If I were traveling for business there's no way I would use the Blue Line unless it was peak rush hour, and indeed most business travelers don't. Getting weed smoke on your work clothes is a less than ideal way to start a trip, nor is getting sweaty in your work clothes from hauling luggage around the station.
Thus the case for an express train - it would capture those price insensitive business travelers. You could charge $20 a ticket and it would still be a significant savings over Uber. Heathrow Express in London is like this and it seems to work well.
