Car washes obviously have a significant amount of water. Many of the newer car wash tunnels are long and flat. A central trench drain run the length of the wash bay is an obvious solution to collecting this water.
In some cases, other utilities such as water lines, soap, and mechanical movers are also run inside this drainage / utility trench making it a multi-purpose trench. The trench can also be used as a place to remove sediment by using sand traps or catch basins with baffles.
A trench drain at a car wash rarely ever sees any traffic at all. Usually the worst traffic is pedestrian traffic, so almost any frame and non skid trench grate will work. The exception to this would be any drains that are located at the entrances and exits that receive vehicular traffic.