Abstract: A descending grade condition detecting system which can accurately detect a descending grade such as a snow-packed road or the like where slippage is likely determines whether permission has been granted to perform descending grade determination. If so, it determines whether established vehicle body deceleration is 0.3 G or less. If so, the system determines whether a road surface at each of the wheels is low .mu. corresponding to a snow-packed road or the like. If estimated vehicle body deceleration is small and of comparatively high .mu., descending grade condition flags KF are set for the respective wheels for which determination thereof has been made to indicate that a condition of a road being traveled is a condition of a low .mu. descending grade of a snow-packed road or the like.

Abstract: The wheel speed of each wheel of a vehicle is calculated based on wheel speed signals from wheel speed sensors. The wheel acceleration of each wheel is calculated based on the wheel speed. High frequency components of the wheel acceleration of each wheel are filtered using a high-pass filter to obtain the frequency components of the wheel acceleration which are due only to the road surface condition. Then, a variance of the filtered wheel acceleration is calculated, and a bad road condition determination is executed using the calculated variance. Anti-skid control is carried out based on the bad road condition determination result to provide improved braking control in off-road conditions.