Rain - do you know how to change tires/flats/etc? If you take a maintenance course of some sort, you might be more confident in your ability to ride by yourself... I ride by myself most of the time on sort of random routes - but I do carry spare innertubes and tools with me, enough that I'm pretty sure I could get myself home if I had to... otherwise, I have my cell phone and can phone for help.. even if I might have to wait a couple hours before someone could get to me.

Otherwise you could maybe plot out some routes that go around metro stations... so you know that if something went wrong, you could just take the metro and get out of there.