A computer includes a processor and a memory, the memory storing instructions executable by the processor to detect an actual steering column torque and an actual steering wheel angle, predict a steering wheel torque with a state-estimation algorithm that outputs a plurality of vehicle states including the predicted steering wheel torque, adjust the plurality of vehicle states based on an algorithm noise that is based on a steering wheel angular speed to generate estimated vehicle states, output the estimated vehicle states including an estimated user-applied steering wheel torque, and transition from an autonomous mode to a manual mode when the estimated steering wheel torque exceeds a threshold. The state-estimation algorithm accepts input including the actual steering column torque and the actual steering wheel angle and outputs the plurality of vehicle states.