[op00to]

American Airlines also shows busses as flights from EWR to PHL. :)

[jeffbee]

Now there's a route where I would certainly choose Amtrak over air.

[op00to]

As far as I can tell, you clear security the normal way at your origin airport, and enter inside security at the intermediate hop. Not a terrible way to travel, I think. With taxi time and delays at EWR, it might not even be that much slower!