There are no speed restrictions. I've run trains at 60 smph over it. It is an 8' two track semicircle 3' high at it's tallest point. There are 23,000 nbw castings attached to it. The brass rods on the bridges are actually threaded with 00-90 treads w/ matching nuts. The bents are made in 6" tall sections, stacked and glued. I made jigs for each section, then jigs to stack the completed sections. It was built upside down and took 4 people 5-1/2 hours to flip it and put it in place. There are 1,100 trestle ties with 6,600 spikes. It took 3 years to finish. I had a friend who was helping me design the layout because it was the first I've ever done. I told him I wanted a trestle and asked him how big I should make it. He said make as big as possible so I did. He had a cad drawing of a bent that he blew up to actual size and I used that as the guide. Where I worked I had access to a Bridgeport mill and I used that to mill out pieces of acrylic for the jigs to make sure the jigs were perfectly parallel top to bottom. If I had known what I was getting into I would have made it a lot smaller. lol. It is very sturdy. Every upright post has a screw on top and bottom. I never actually counted them but it was between 3 and 4 thousand.
I can say with certainty that I'll never have anything like that on my layout, I probably won't live long enough to get it built! 
