There are a number of reasons why it is dangerous to drive after rain or to drive in the rain. When you drive after rain, you should be aware that the surface of the road is covered in a thin film of water, oil, and grease which can reduce your traction and cause your car to skid. While driving in the rain, you also have to contend with poor visibility. By driving slowly and staying focused, you will prevent accidents which may cause damages, injuries, or loss of life. It is also very important to keep your tires well maintained for the best possible traction.
Rain makes for slippery roads, especially when it has not rained in a long time. This is because greasy substances like lubricants and oil drip from cars as people drive, and these substances accumulate on the surface of the road until they are washed away. The first rain can loosen these greasy materials, creating an oily slick on the surface of the road which can make driving very dangerous. If you drive after rain, you need to be aware that this slick can interfere with your ability to drive, especially at high speeds.
A long, hard rain can also cause deep puddles on the surface of the road which may cause your car to hydroplane, essentially skimming across the water. Poorly drained roads can be covered in huge pools of water which may not seem deep or serious until you drive on them and your car spins out of control. You should avoid puddles whenever possible when you drive after rain, and you should drive slowly through puddles if you cannot go around them to avoid hydroplaning.
In the rain, poor visibility is a major threat to driving safety, as you may be less aware of oncoming cars, pedestrians, and hazards in the road. It is important to have good windshield wipers, and it helps to leave your lights on and drive slowly in the rain so that you are better prepared for unexpected hazards. This is especially important in stormy weather, when you may have to contend with falling tree branches, downed power lines, or mudslides during your drive. If you can avoid it, do not drive in hazardous weather conditions.
If you do end up in a skid when you drive after rain, the most important thing to do is stay calm. Steer gently into the skid and stop accelerating, allowing the car to find the road again. If you have antilock brakes, depress them firmly as you are coming out of the skid to bring your car to a stop; if you do not have antilock brakes, pump your brakes once the car has found the road again. You may also want to flash your lights or turn your hazards on, to alert other cars in the road to the fact that you are having a problem.