Speed ​​detection is one of the most well-known functions of our local and state police. How do they know how fast we're going? Speed ​​determination is done in two basic ways. First, the least sophisticated method depends on the officer's ability to guess your speed. Second, some electronic method using radar or laser instrumentation authenticates the officer's hypothesis. As you'll see, their guesses are usually right. What does this mean for you? Usually a speeding fine or, if the offense is not a flagrant safety violation, a friendly warning. Speed ​​is the distance traveled divided by the total time taken to go from the starting point to the ending point, or:s =(Dx)/(Dt)How does the speedometer work?Your vehicle's speedometer determines your speed by examining the speed angular(v) of your axle (the speed at which the axle turns) and multiplying it by the manufacturer's recommended circumference for the circumference of your vehicle tires. (This is why using oversized tires will cause the speedometer to register a lower speed than the actual travel speed: the circumference of oversized tires is larger than that of recommended tires, while the angular speed remains the same) So, in the application: s = v*2prWhy should we limit our speed? Speed ​​limits are established for roads based on road characteristics such as geometry and capacity, and traffic characteristics such as overall volume, hourly volume, and traffic density. Speed ​​limits are designed to regulate traffic in the most effective and safe way. There are several methods of manually tracking speed, but they all rely on obtaining a known distance and comparing it to the time it takes to travel that distance. Officers who have been observing traffic for a long time tend to have a very good understanding of how fast vehicles are traveling. Shown below is a table showing an officer's assumptions along with an inexperienced observer's assumptions and radar results. Keep in mind that Officer Keeler's guesses are all within 3 mph of actual speed. My guesses tend to have a greater deviation and have sometimes been influenced by Agent Keeler's guesses if he had spoken first. The other methods include using a stopwatch and timing a vehicle over a known distance, from the ground or in an aircraft, and pacing a vehicle's pace. Pacing a vehicle involves matching speeds to the vehicle and checking the speedometer or finding distinct markings and counting so you can divide the distance by the time again to get a speed.