Major sections of I-95 north of downtown Philly will be rebuilt and repaired starting May 17. This is a 2 year project. See full story at...
inq.philly.com/content/inquirer/2001/05/04/front_page/PREVIVE04.htm
PennDOT's has a site for construction updates
www.95revive.com.
Watch out for snarled traffic South-bound from Trenton into Philly in the mornings, and the other way in the evenings. There was a fire underneath the highway a few years back that forced lane closures for a long time, and traffic was a nightmare during that time.
To go from PHL to points North of Philly like Princeton and Trenton, I'd suggest crossing over to New Jersey on the Walt Whitmam Bridge and using I-295 North.