A patient transport apparatus transports a patient over a surface. The patient transport apparatus comprises a support structure comprising a base, a patient support surface, and a reference sensor arranged to sense inclination of the support structure. A drive system is coupled to the support structure and operable to propel the patient transport apparatus. A handle assembly is operable by a user to control operation of the drive system. The handle assembly comprises a handle movable relative to the base and a position sensor arranged to sense positioning of the handle. A controller is coupled to the reference sensor and the position sensor, and is adapted to control the drive system in response to signals received from the reference sensor and the position sensor.