Supported on the long edges. https://files.engineering.com/getfile.aspx?folder=008e9c80-b8fa-4248-bda0-9ad5ff42ae3b&file=C96259EB-4EBB-4BE7-916A-CEABBA5F21CE.jpeg
I'm sorry, I'm pretty new to all this. This 1/4" thick, 12" wide by 60" long plate would be supported on the edges as it's intended on being a ramp for an aggressive curb (just about a 90° angle). So the load would be rolling from the bottom to top.