I live in south Jersey, too, and volunteered at CHOP for awhile. (I'm still a student.) There's no easy way to say it. The commute is brutal, and the time of day hardly has any effect on it. It's almost ALWAYS bad. It's that darn Schulkyll (sp?) Expressway, which seriously needs to be re-worked. The part I hated the most was leaving a shift and having to merge onto that horrible expressway into the LEFT (fast) lane of traffic, with cars coming at you at about 80 mph.
However, I'd hardly let that deter you from accepting a job at Penn! That's fabulous! Good for you! What a prestigious place to work. Seriously. I'd love to work at Penn or CHOP one day...but if I did, I would seriously consider using public transportation, depending on where in SJ you live. Almost any time I go into Philly, I take the PATCO trains. They don't go all the way to the university area up there, but there is a pretty busy bus/train (?) stop about a block from the hospital. If you look into something like this, you kill two birds with one stone: no driving traffic, and no parking hassles. I don't know much about parking at the complex down there, but traffic is a total nightmare, even on campus, and they provided free parking for volunteers, but I think employees have to pay to park at any number of parking garages on the campus. Of course trains, busses, etc. will add commute time to your already long day, but as someone who has used public transportation to get to work before, it can be nice and relaxing "down" time.
So what unit will you be on if you take the job? Would love to hear all about it, and how you landed such a great opportunity. Good luck in making this decision. Personally, I'd go for it! Keep us posted!