Based on statistics collected by the National Highway Traffic Safety Administration, in the United States alone there are approximately 6 million auto accidents each year. These accidents result in nearly 33,000 fatalities and billions of dollars in damages from both property damage, medical expenses and lost productivity One half or about 3 million of these accidents result in some type of bodily injury. Of these 6 million accidents, about 1/3 or 2,000,000 are rear end collisions that occur when a driver does not see a slower or stopped vehicle in front of them in time to stop or take evasive action. (Source - National Highway Traffic Safety Administration - 2016)
In other words, for various reasons, the vehicle was not visible to the approaching driver in time to prevent a collision. And because of this thousands of people lose their life each year.
The scenario is similar but worse for commercial vehicles. Based on a study by the US Department of Transportation there are about 400,000 accidents each year that involve large trucks with a gross vehicle weight of over 10,000 each. Out of these 400,000 accidents, 5,000 resulted in fatalities, 109,000 resulted in bodily injury, and all resulted in some type of property damage. Source -
(Note - Fatalities for large truck accidents are 2.5 times higher on average than vehicle accidents as a whole.)
Overall, vehicle accidents in the US alone cost $871 billion dollars each year. The vast majority of vehicle accidents are avoidable. Careless driving, speeding, drunk driving, distracted driving, dangerous road conditions, and fatigue kill thousands of people each year on Americas highways.