SAN FRANCISCO — EVERYBODY who knows me knows that I love cycling and that I’m also completely freaked out by it. I got into the sport for middle-aged reasons: fat; creaky knees; the delusional vanity of tight shorts. Registering for a triathlon, I took my first ride in decades. Wind in my hair, smile on my face, I decided instantly that I would bike everywhere like all those beautiful hipster kids on fixies. Within minutes, however, I watched an S.U.V. hit another cyclist, and then I got my own front wheel stuck in a streetcar track, sending me to the pavement.
I made it home alive and bought a stationary bike trainer and workout DVDs with the ex-pro Robbie Ventura guiding virtual rides on Wisconsin farm roads, so that I could sweat safely in my California basement. Then I called my buddy Russ, one of 13,500 daily bike commuters in Washington, D.C. Russ swore cycling was harmless but confessed to awakening recently in a Level 4 trauma center, having been hit by a car he could not remember. Still, Russ insisted I could avoid harm by assuming that every driver was “a mouth-breathing drug addict with a murderous hatred for cyclists.”