well being a trucker and one that has hauled just about every trailer you can think of. I can attest that many lowboy trailers often are only about 6"-12" of the ground (center of the trailer) trailer hight can depend on if the truck has spring or air ride suspension, machine is pushing the max hight restriction(13'-6") or is hauling a heavy load and is bending the center of the trailer. you can compensate the trailer hight with alot of newer trailers but many older ones you stuck with where it sits. I have come across many RR crossings that have no signs warning of a steep grade to and after the tracks. This has always been a problem and only truckers that know the aera will know what the trailer can or cant clear. being a good trucker i can scope out what will work, might work and what wont. 8 years ago I was dragged to a stop over a set of RR tracks. I was hauling a cat 963 track loader( about 90k gross truck weight) I came up to a intersection that parralled the tracks. I was making a right turn, went up over the tracks and I had to make another right just after the tracks. I had gone over this set of tracks many times with lighter machines and a simmilar model low boy trailer. So I thought it was safe with the 963. well as soon as my tractor went over the crossing the middle of the trailer slid across the pavment and I was dragged to a stop. knowing that I could change the hight of the trailer with the hyd system. I put the PTO in, got out and raised the deck a little relying on the hyd rams to hold the trailer up a few inches more to get over the hump. as soon as I was clear I got back out to lower the deck and let it rest metal to metal on the gooseneck. if a guy is in a hurry and does not know some simple tricks lowboys can get you stuck crawling over something as small as a large curb.
