Toyota PRIUS Manual page 366

2-4. Using other driving systems
Dynamic radar cruise control can be set when

 The shift position is in D.
 Vehicle speed is above approximately 50 km/h (30 mph).
 Accelerating after setting the vehicle speed
The vehicle can accelerate normally. After acceleration, the set speed
resumes. However, during vehicle-to-vehicle distance control mode, the
vehicle speed may decrease below the set speed in order to maintain the
distance to the vehicle ahead.
 Set speed
The set speed may be unsustainable depending on driving circumstances.
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PRIUS PHV_OM_OM47831E_(EE)
If the "POWER" switch is turned
off and then turned to ON mode
again, the vehicle will automati-
cally return to vehicle-to-vehicle
distance control mode.
Adjusting the speed setting:
P. 359
Canceling and resuming
speed setting: P. 361
the