I have two artificial plates in my head from a bicycling accident in 1991 when I was an undergraduate. I am fine now, but I lost a year out of school (still graduated in four years anyway, then on to a Ph.D., etc)
Years later, I loved riding my bike through Pacific Spirit Park on my daily commute to UBC when I was a postdoc in Vancouver years ago, and I miss it. Still, despite all the fanatical devotion to biking around here I would NOT ride my bike ANYWHERE within 250 miles of the irredeemable hellhole of SoCal, where I currently live. SoCal is NOT the place to be on a bike. Drivers are distracted and stupid everywhere, but--as with EVERYTHING else--it's worse, much worse in SoCal.
Helmet or not, you are no match for a SUX 6000 SUV driven by suburban soccer mom, checking the facebook, drinking the latte, catching Pokemon, petting the dog on her lap, screaming at the kids, etc.
I don't care how much money it would save me (is not practical for my route, profession, or the HOT weather here anyway), it is NOT worth the risk. One slight miscalculation on the part of some retard driver and you're dead...So much for FIRE