I have a four hour layover in Philadelphia in late September. I'm flying on to Italy afterward.

I'd really love to get into the city and see a little bit of it (quickly). Do you think this is possible with the time that I have? How long does it take to get from the airport to the city via taxi?

Thank you!

You're supposed to check in at least 2 hours before your international flight.
The Philly airport is way south of the city. A cab ride might get you to Center City in 30 minutes if traffic's light, but that's an hour round trip.
If ANYTHING went wrong, you could miss your flight.
Not worth it IMO.

The Philadelphia Airport is 8 miles south of downtown. A cab would take about 20 minutes. There is a flat rate of $20 between downtown and the airport.

I agree with Ted that it might be cutting it close for your flight if you leave the airport. It all depends when you are arriving. If it's during rush hour 7-9 AM or 3-7 PM I would just stay at the airport. There are lots of shops and restaurants there to keep you occupied. You could even go to the Airport Marriot, which is connected to the terminal building, for lunch and to relax.

You could take the train from the airport, which is shorter time wise but since security takes so long, I wouldn't chance missing my Italy flight, unless its late.

But couldn't Erin74 check in when she arrives, check all luggage, and get boarding pass(es).