Originally Posted by
sonofzeus
Pops can take a city cab (metered), suburban cab (cheaper fixed price, reserved ahead only) or
this.
A suburban cab can't legally do that route, both ends are in the city.
OP, you probably have some idea of whether your dad will be comfortable in the city and with public transit or not. If he will be and can do the stairs, walking to the train is fine. Ignore the post about him getting mugged to save a few bucks, it's rush hour, it won't happen. If the stairs are not good, but the train is, cab to Jackson/Dearborn or Clark/Lake (handicap-accessible does mean elevators).
If he won't be comfortable or has mobility issues, then either cab or Airport Express is a fine option.
The other thing to mention is that he has time to sightsee (thought of this due to the threads we get here asking if X is enough of a layover at ORD to go into the city). I'd allow 75 mins to get to the airport plus whatever time he needs at the airport (ie 90 if checking bags, 120 if int'l, etc). So, if the train is on time, that 5 hours gives him a little time to wander around if he so desires.