What should you assume when passing a vehicle, pedestrian, or bicycle?

Vehicles may be partly hidden by blind intersections or alleys. If you only can see the rear or front end of a vehicle but not the driver, then he or she cannot see you. Be alert because they may back out or enter into your lane. Always be prepared to stop. Walkers, joggers, and bicyclists may be on the road with their back to the traffic, so they cannot see you. Sometimes they wear portable stereos with headsets, so they cannot hear you either. This can be dangerous. On rainy days, pedestrians may not see you because of hats or umbrellas. They may be hurrying out of the rain and may not pay attention to the traffic. [California Commercial Driver Handbook]