There was an overturned tandem tractor trailer this morning in north St. Louis. This incident has nothing to do with traffic jams or some such, but I've seen these double trailer trucks on the highway and honestly, they're scary. Trucks are big enough as it is these days, too tall, too long, too wide. When one of the huge trucks with only a single trailer passes you it seems like it's a city block long. But with two of these hooked together they sway side to side until all you want to do when nearby is get away from it.
The most common company using the tandem tractor trailers that I've noticed is FedEx and they move the fastest on the interstates compared to other freight hauling trucks. They zoom.