Toyota 2015 Prius Owner's Manual page 315

Operating conditions for each function
Lane departure warning function
■
● When the vehicle speed is approximately 30 mph (48 km/h) or
more
● When the lane width is more than approximately 9.1 ft. (2.8 m)
● When driving on a straight road or through a curve with a radius
of more than approximately 394 ft. (120 m)
Lane keeping assist function
■
● When the vehicle speed is between approximately 45 and 112
mph (72 and 180 km/h)
● When the vehicle-to-vehicle distance mode of the radar cruise
control is on, and the set vehicle speed is approximately 45 mph
(72 km/h) or more (the function will not operate when the radar
cruise control is in set speed mode)
● When the lane width is between approximately 9.1 and 13.1 ft.
(2.8 and 4.0 m)
● When driving on a straight road or through a curve with a radius
of more than approximately 656 ft. (200 m)
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2-4. Using other driving systems
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