TOYOTA 2010 Sienna - Manual (Page 228)

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2-4. Using other driving systems
Driving in vehicle-to-vehicle distance control mode
This mode employs a laser radar sensor to detect the presence of
vehicles within 400 ft. (120 m) ahead and to judge the distance
between your vehicle and those vehicles.
Note that vehicle-to-vehicle distance will close when traveling on long
downhill slopes.
Example of constant speed cruising (when there are no vehicles
ahead):
When set to 62 mph (100 km/h)
The vehicle travels at the speed set by the driver. The desired vehicle-to-
vehicle distance can also be set by operating the vehicle-to-vehicle dis-
tance switch.
Example of deceleration cruising (when the vehicle ahead is driv-
ing slower than the set speed):
When fixed speed cruising is set at 62 mph (100 km/h) and the
vehicle ahead is driving at 50 mph (80 km/h)
When a vehicle is detected running ahead of you, in the same lane, the
system automatically decelerates your vehicle. When a greater reduction
in vehicle speed is necessary, the system applies the brakes. A warning
tone warns you when the system cannot decelerate sufficiently to prevent
your vehicle from closing on the vehicle ahead.