Off-topic, but while Marquisse is gone, shh! - aren't there workplace safety rules against truckers clearing their trailer tops of ice? It's above the height limit where you need to be tied off, and there is no place to tie off to. At least that's what I've heard.
Hey now, that's not very nice, Squishy.
There is a serious hazard to it because there is no way to safely do so. They have to get up and chisel the ice, which can get thick, off the top of the trailer. Employment legislation prohibits workers from climbing without approved safety equipment.
My friend and her hubby have owned a trucking company for 16 years (was her hubby's Dad's) and the ice falling is treated much the same way as debris falling from the truck, unless someone is seriously hurt or killed, or major calamity such as multi-vehicle accidents occurs, and the discretion lies with the officer to broadly interpret legislation. In those cases, charges are often laid. There are currently no laws on the books relating directly to this, except for Quebec. Private members' bills have shown up often only to die off, and usually happen when such a calamity happens as a result of falling ice. It's a vastly under-appreciated hazard, largely ignored by both the commercial trucking industry and the government. Some of these ice sheets can weight in the tonnes.