Toyota 2014 Sienna Manual page 352

2-4. Using other driving systems
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
352
SIENNA_OM_OM45483U_(U)
Speed
18 mph (28 km/h)
5 mph (8 km/h)
Approximate
alert distance
65 ft. (20 m)
18 ft (5.5 m)