In an urban setting I would be happier with a medium sized crowbar and good pocket knife rather than just a big knife. Ideally my DF and a crowbar. Breaking glass, prying doors off hinges...none of this stuff is what knives are really good at. And if you're stuck in the land of concrete and glass this is what I would expect to be doing. The knife might be needed for cutting your way out of conduit and fallen cables and I would really prefer a rubber handled knife for that.

A crowbar can be a pretty intimidating weapon if you found yourself in a bad situation. A pistol still trumps a crowbar though for self-defense.