In some countries (for example, United States), aircraft may be used for aerial speed enforcement. This way of enforcement is also known as aircraft VASCAR speed enforcement. A police aircraft may have speed-measuring equipment onboard. Then, when flying over a highway, an officer in the aircraft clocks vehicles on the highway. If they find a violator, they direct a ground unit to the vehicle over the radio so that an officer can issue a ticket.
Highway Radar has a built-in mechanism for alerting drivers on proximity aircraft, which may potentially do speed enforcement. Highway Radar connects to ADS-B exchange networks (what is ADS-B?), then attempts to detect which nearby aircraft can do speed enforcement, and displays them to the user. The aircraft alerting mechanism doesn't require any configuration and works out of the box.
It is essential to understand that Highway Radar tries to filter out aircraft which can't do speed enforcement (e.g., not alerting on passenger Boeings or flight school-owned aircraft). If the application didn't do that and alerted on every aircraft above, it would have become unusable. Because of the filtering, sometimes it may seem the aircraft alerts aren't working – especially if you see an airplane with your eyes but don't see it in the app. There is a way to make Highway Radar display all aircraft (
Settings > Aircraft alerts > Choose which aircraft to show > All aircraft, including safe). However, we don't recommend using the application with all aircraft enabled. The all aircraft mode is only suggested to verify that the application is pulling the aircraft data.