In America, traffic police help keep people safe. It is their job. They direct( 管理) traffic around schools, events, and accidents. But, sometimes, people don't like police when they give them tickets for speeding. The speed limits (限速) are lower(低的) around schools, in the downtown areas of a city. Speed limits help drivers and walkers. To keep people safe, police must make sure that people follow the speed limits on streets. When people get tickets for speeding, they must pay a fine. Police hope that paying the fine will make the drivers slow( 慢的) down and obey the speed limit. So how does a police know that a driver is moving too fast? Can they tell by just looking at a moving car? In fact, police use a special tool(工具) to help them find drivers who are moving too fast. The tool is radar guns (雷达枪). Police put radar guns in their cars. They point the gun at passing cars and the gun shows the speed of each car.
