I had no idea such a limit existed. But there it was. Last Friday afternoon, I was heading to the Ontario-Michigan border with that plan to hit up nearby a shop or two for at least three cases of various craft beers when, whammo, traffic stopped. Almost two miles from the border, everything stood still. For ten minutes not a tap on the gas, not a hint that something was in motion up ahead. The border information radio station gave the wait as one hour. My quick math gave me a result of over twice that and about as much to return later after spending less than one hour in the USA.
It didn't help that the van was making this squeeling noise like a bearing about to explode or that the news all day was about how the Canadian dollar had dropped about 4.5% against the greenback. So, after a quarter hour or so, I slipped down the side of the road and hit exit 2 turning north and then north-east along southern shore of Lake Huron back to where I started.