I have built free standing inclined subroadbed ramps and upper level roadbeds out of thin 5.5mm Meranti plywood and made tapered rising walls out of bendable plywood which can conform to any curve(s).
Very light weight but you can stand any where on the incline section. Lots of rigid structural integrity and can be lifted up at will without flexing. One 4X8 sheet of Meranti and one 4X8 sheet of bendable plywood would more than do the track pan shown in the photos.
Additionally, using the bendable plywood to form the ramp profile allows you to gently form the vertical curves at the bottom and top of the ramp. Real slick finished product, no abrupt vertical angles.
It is not necessarily the thickness of the plywood but more so the construction techniques used that develops the strength and rigidity.
