What instrument is used to determine the speeds of approaching vehicles in the field?

• A. Radar
• B. Stopwatch
• C. Speed Gun
• D. Lidar

Answer: (A)

Measuring the speed of moving vehicles in the field relies on detecting how waves change when they bounce off a moving target. Radar does this by emitting radio waves, which bounce off the vehicle and return to the instrument. The device detects a Doppler shift in the reflected waves, and from that shift it computes the vehicle’s speed relative to the observer. This gives an immediate, distance-based reading without needing to time how long a car travels a measured distance or rely on the operator’s reaction time. A stopwatch would require precise timing over a known distance, which is impractical in real traffic, and while lidar can also measure speed using laser light, radar is the standard field instrument for determining speeds quickly and reliably.