A number of causes can contribute to California cycling accidents. Cyclists often share the road with other vehicles and pedestrians, which presents the opportunity for collisions and accidents. Sometimes cyclists ride in large groups, which can lead to accidents involving other bicyclists. Each year, hundreds of bicyclists are killed in accidents that are caused by negligent automobile drivers who are distracted or do not see them. Many bicycle accidents also happen when a cyclist loses control of his bike and crashes into a stationary object such as a pole, curb or median. Injuries can also be caused by defective bicycle parts or unsafe riding conditions.