Toyota PRIUS 50 2020 Series Owner's Manual page 311

The Rear Cross Traffic Alert function detection areas
The areas that vehicles can be detected in are outlined below.
To give the driver a more consistent time to react, the buzzer can alert
for faster vehicles from farther away.
Example:
Approaching vehicle
Fast
Slow
■
The Rear Cross Traffic Alert function is operational when
●
The BSM system is set to on. (P. 126)
●
The shift position is in R.
●
Vehicle speed is less than approximately 8 km/h (5 mph).
●
Approaching vehicle speed is between approximately 8 km/h (5 mph) and
28 km/h (18 mph).
4-5. Using the driving support systems
Speed
28 km/h (18 mph)
8 km/h (5 mph)
309
1 Approximate
alert distance
20 m (65 ft.)
5.5 m (18 ft.)
4