Some of my former co-workers at med center used to drive from Kingwood, depending on what time you drive in, it can be as little as 20-30 minutes. I'm not kidding! It might be worth it to commute or to use a Park and Ride system, but it didn't seem like they didnt had to travel far to get down to the med center and they love it there. You just have to figure out what peak traffic times in Houston are and just go around that. In Houston rush hour usually runs from 6am -10 am and 3pm - 6:30pm which is great because all the hospitals in the med center are 12 hour shifts.
Good luck with your decisions!