There are many differences between America and China. The biggest difference is traffic rules. In America there are too much more cars than in China. But there are much fewer traffic jams and accidents in America than in China. We hardly see traffic police in the street, but all cars obey strictly traffic rules, and people hardly find that a car does not obey traffic rules in the street. About American traffic rules, there are many better terms, such as: 1. Stop line: There are stop lines in all crossing without traffic light (some have two stop lines and others have four stop lines). All cars must stop while meeting the stop line. 2. Traffic light: There is traffic light in the crossing of the road. Cars may almost turn every direction. The traffic light can give signal step by step including u-turn. There is a kind of middle lane of turning left. When a car wants to turn left in the road, he may enter into the middle lane of turning left and give a signal of turning left. When he thinks being safe, he may turn left. In many conditions the order of passing is also given very specifically. If people want to change lane or turn, they must look behind and think being safe. Only so, they may do it. 3. Specific item: Such as parking, there are three kinds of lines (their colors are white, blue or red) in the roadside. Every line may park different kinds of cars. There are many streets in some residential areas  , and there is a kind of rule that any car cannot park at any time or any period time. In every parking, there are some special positions for invalid   people. 4. About the priority of passenger and car: At any case, passengers have the priority to cars. And only after passengers have passed the road and got the top of sidestep, cars may go ahead. In general, traffic rules of America are very specific, convenient, safe and humanizing. Why is there a middle lane of turning left on the road?
It is designed for the cars that want to turn left. It is very safe to drive there. It is very convenient for the traffic police to find the cars that break the rules. The cars that want to turn left can easily give a signal of turning left.