A computer for, e.g., a mass market passenger vehicle operable by a virtual driver in autonomous and/or semi-autonomous mode, is programmed to determine that a current vehicle braking capacity exceeds each of a first braking target and a mitigation threshold at a current vehicle speed. The computer is further programmed to compare the current vehicle speed to an engine breaking threshold and generate a transmission control message providing data to operate a vehicle transmission. Where the current vehicle speed is above the engine braking threshold, the transmission control message provides data to operate the vehicle transmission to inhibit transfer of an input torque through the vehicle transmission. Additionally, where the current vehicle speed is below a wheel lock threshold, the transmission control message further provides data to operate the vehicle transmission to inhibit rotation of an output shaft of the vehicle transmission.