A bicycle is a small, light, unprotected frame. A car (or a truck or a bus) is a massive and often unpredictable object. In any confrontation, the bike will lose, so a cyclist must ride as if his life depended on it. It does.
A cyclist should assume that all drivers are antisocial, taxi-drivers in particular, and that Metrobus drivers invest in cemeteries and funeral homes. No matter how beautiful the day, the scenery or the pedestrians, self-defense must be where your mind is.
Several things can lower your chances of sudden extinction. The bike should be kept in top condition. A helmet is a must, especially for commuters; ditto cycling gloves. Clothes should neither be so loose that they get in the way nor so tight that they restrict movement. Use trouser clips so cuffs don't get tangled in the chain. Use bike racks or panniers; backpacks can throw you off balance. Never carry anything in your hands while riding.
Plan your route. Is it hilly, heavily traveled, narrow, slow, fast, smooth, pot-holed? These all determine how to ride; as a general rule, stick to less-crowded streets and learn their potholes. If the weather's bad, take the bus.
If you can't keep within 10 mph of the traffic pace, you shouldn't be on that road. Most one- and three-speed bikes should steer clear of heavily traveled thoroughfares, since a cyclist must be able to keep up with traffic and still work up quick bursts of speed to get out of harm's way -- for instance, when passing a stopped bus that suddenly pulls out into traffic. How important is it to keep up speed? Consider this: A car traveling at 30 mph overtakes a cyclist traveling at 20 mph. Their relative velocity difference is 10 mph. If the bike is going only 10 mph, the velocity difference is 20 mph, so the two vehicles are closing in twice as fast, cutting potential reaction time in half. Biking in traffic is no joyride. For fun, ride in the park where nobody cares if you poke along.
Obey stopsigns, stoplights and one-way signs. Always respect others' right of way.
Some cyclists weave from lane to lane, tailgate, challenge drivers for traffic space and insult taxi drivers. These are people who haven't grown up and aren't likely to grow old. Always signal and look before changing lanes. Cyclists have the same rights of way as other vehicles, but, most of the time, a bicycle doesn't require an entire lane. There are times, however, when it's in the cyclist's interests to claim the whole lane, to avoid squeeze plays.
Even the most experienced or careful rider is sometimes no match for the careless or reckless driver. Of course, drivers (excluding diplomats) are liable for everything they do behind the wheel, and drivers (including diplomats) are liable to do anything once they get behind the wheel. Any experienced rider has tales to tell of being cut off, knocked down and run off the road, usually by carelessness, not malice. It happens every day. You live to tell your stories by dumb luck or quick reactions, but you can help your chances by foresight and careful attention to traffic.
Get to know traffic patterns on frequently traveled routes and find out where trouble is most likely to happen. Then stay away from there.