1. A system for counting riders positioned in a vehicle having an open top for exposing heads of the riders from above the vehicle, the system comprising: a light source structured to provide a focused light beam over the open top of the vehicle; at least one camera; and a computer having a processor configured to: receive, from the at least one camera, video data corresponding to a scan of the vehicle including the riders through the open top of the vehicle exposing the heads of the riders from above the vehicle, as the vehicle passes through the focused light beam; convert the video data into a 3D height map; and analyze the 3D height map to determine a number of the riders in the vehicle by counting the number of heads shown as being exposed through the open top of the vehicle in the 3D height map.