Buick RIVIERA 1993 Manual page 80

1 (First Gear)
Parking Brake
This position gives
you
even more power (but lower
fuel economy) than "2." You can use it on very steep
hills, or in deep snow or mud. If the selector lever is
put in "1," the transaxle won't shift into first gear
until the vehicle is going slowly enough.
The parking brakes uses the brakes on the rear wheels.
To set the parking brake:
Hold the regular brake pedal down with your right foot.
Push down the parking brake pedal with your left foot.
If the ignition is on, the brake system warning light will
come on.