Road friction and wheel slippage assessment for autonomous vehicles

A method of controlling a vehicle operating in an autonomous driving mode in response to wheel slippage, the method comprising:

• receiving, by one or more processors of an autonomous driving computing system, a measured rotational wheel speed of each wheel of a plurality of wheels of the vehicle while operating in the autonomous driving mode;
• for each wheel of the plurality of wheels, determining, by the one or more processors of the autonomous driving computing system, an expected rotational wheel speed for that wheel, wherein the expected rotational wheel speed is determined based on actuation commands sent by the one or more processors to one or more systems of the vehicle;
• for each wheel of the plurality of wheels, comparing, by the one or more processors of the autonomous driving computing system, the measured rotational wheel speed for that wheel to the expected rotational wheel speed for that wheel to determine a difference between the measured rotational wheel speed for that wheel and the expected rotational wheel speed for that wheel;
• and
• when the difference for one or more wheels of the plurality of wheels meets a threshold, controlling, by the one or more processors of the autonomous driving system, the vehicle in the autonomous driving mode to change trajectory along a route to a destination.