A drive-over tire tread depth measurement system is configured with environmental protection components for preventing or impeding environmental contaminates from falling through openings in a vehicle support surface or cover plate onto underlying components such as sensor optical windows and adjacent surfaces. The environmental protection components may include air discharge assemblies, movable shields, guards, wipers or deflectors such as drip edges, water-accumulating textured surfaces, flow diverters, and selectively placed flanges or fixed guards which operate cooperatively to displace accumulated contaminates, debris, or liquids from the optical windows and adjacent sensor surfaces. A portion of the vehicle support surface or cover plate is removable to permit access to underlying components.