According to the passage, why winter driving is dangerous?

Winter driving is dangerous because it is so difficult to know what is going to happen and accidents take place so easily. Ice might be hiding beneath the melting snow, waiting to send you off the road. The car coming towards you may suddenly slide across the road.
    Rule Number One for driving on icy roads is to drive smoothly. Uneven movements can suddenly make a car very difficult to control. So every time you turn the wheel, touch the brakes or increase your speed, you must be as gentle and slow as possible. Imagine you are driving with a full cup of hot coffee on the seat next to you. Drive so that you would not spill it.
    Rule Number Two is to pay attention to what might happen. The more ice there is, the farther down the road you have to look. Test how long it takes to stop by gently braking. Remember that you may be driving more quickly than you think.
    In general, double your normal stopping distance when the road is wet, three times this distance on snow, and even more on ice. Try to stay in control of your car at all times and you will avoid trouble.