Many fixtures have flat load ratings, but we have an actual DOT rated fixture, which is the 9360DO. (DO stands for drive-over)
Used at border stations, etc. Tested by independent laboratories. The static load stuff is okay for pneumatic tires, golf carts, etc, but we wouldn’t recommend it for driveways, etc. 9360OD has a big brass grate.
Spec sheets: http://www.acuitybrands.com/products/detail/47109/hydrel/9360-do/well-light/spec-sheets