Determining Alert Severity

Aircraft alert severity is determined based on the following parameters

  • Aircraft distance to the driver
  • Aircraft altitude
  • Aircraft speed \(V\)
    if less than 50 m/s (~100 kt), use 50 m/s instead
  • Kill zone angle \(\alpha\)
    Determined by the sensitivity preference – the values are 60°, 50°, 40°, 30°, 20°, 15°, 10°
  • Kill zone extension time \(E\)
    Determined by the sensitivity preference – the values are 0s, 10s, 20s, 30s, 45s, 1m, 2m

Defining A Kill Zone

Kill zone is an air space above your location from where we consider an enforcement aircraft can clock the vehicle.

Highway Radar considers the kill zone as a spherical sector with a tip at the driver position, extending upward, having a radius of 2000 meters (6562 ft), and a half cone angle \(\phi = 90° - \alpha\).

Severity estimation

Computing Severity

Aircraft alert severity in Highway Radar is computed from the time required by the aircraft to reach the kill zone.

  • 5 dots mean that the aircraft is inside the kill zone
  • 4 dots mean that the aircraft need 0-30 seconds to reach the kill zone
  • 3 dots mean that the aircraft need 30-60 seconds to reach the kill zone
  • 2 dots mean that the aircraft need 60-90 seconds to reach the kill zone
  • 1 dot means that the aircraft need 90-120 seconds to reach the kill zone
  • If the alert is inactive, then the aircraft needs more than 2 minutes to reach the kill zone

Once the kill zone is defined, the following rules apply to find out alert severity.

  • If the aircraft is inside the kill zone, set the maximum possible severity (5).
  • Otherwise, considering the aircraft speed \(V\), and assuming its ability of climbing and descending at a rate of up to 5 m/s (~1000 ft/min), compute time to kill zone \(T\) - the minimum possible time for the aircraft to reach the kill zone if it follows the optimal path.
  • Then compute the adjusted time to kill zone \(T' = T - E\)
  • If \(T' \le 0\), then set the maximum possible severity (5)
  • Otherwise, compute the raw severity value \(S = 5 - \lceil \frac{T'}{30s} \rceil\)
  • If \(S \le 0\), then mark alert inactive, as the aircraft isn't in proximity
  • Otherwise, consider the alert active and set its severity to \(S\)

Please note that the algorithm above doesn't take the driver's speed and location into account – it doesn't adjust the severity values depending on whether the driver is approaching or receding from the aircraft.