The motor vehicle has killed and disabled more people in its brief history than any bomb or weapon ever invented. Much of the blood on the street flows essentially from uncivil behavior of drivers who refuse to respect the legal and moral rights of others. So the massacre   on the road may be regarded as a social problem . In fact, the enemies of society on wheels are rather harmless people just ordinary people acting carelessly, you might say. But it is a principle both of law and common morality that carelessness is no excuse when one's actions could bring death or damage to others. A minority of the killers go even beyond carelessness to total negligence  . Researchers have pointed out that as many as 80 percent of all automobile accidents can result from the psychological condition of the driver. Emotional upsets can affect drivers' reactions, slow their judgment, and blind them to dangers that might otherwise be clear. The experts warn that it is important for every driver to make a conscious effort to keep one's emotion under control. Yet the irresponsibility that accounts for much of the problem is not only caused by drivers. Street walkers regularly go against traffic rules, they are to blame in most vehicle walker accidents , and many cyclists even believe that they don't obey the basic rules of the road. Significant legal advances have been made towards safer driving in the past few years. Safety standards for vehicle have been raised both at the point of manufacture   and through regular road-worthiness inspections  . In addition, speed limits have been lowered. Due to these measures, the accident rate has decreased. But the accident experts still worry because there has been little or no improvement in the way drivers behave. The only real and lasting solution, say the experts, is to convince people that driving is a skilled task requiring constant care and concentration. Those who fail to do all these things present a threat to those with whom they share the road. What is the author's main purpose in writing this passage?
To show that the motor vehicle is a very dangerous invention. To promote understanding between careless drivers and street walkers. To discuss traffic problems and suggest possible solutions. To warn drivers of the importance of safe driving.