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 $$\phi = 90° - \alpha$$.

### 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.