A handlebar assembly for steering a vehicle includes a handlebar, a grip positioned on the handlebar at a first end of the handlebar assembly, and a hand control assembly positioned adjacent the grip. The hand control assembly includes an optical sensor. The optical sensor has a housing with a light transmissive section, a light source configured to emit light, and a light sensor configured to detect light. The light source and the light sensor are positioned at least partially within the housing. The optical sensor is operable to detect movement of a vehicle operator along the light transmissive section of the housing by detecting reflected light from the light source with the light sensor.