Скачать или смотреть Truck with trailer skirts

Originally I posted this as to find out the true purpose of the skirts. I've been told by a couple users that these are for better fuel economy. Now I'm going to leave this here for educational purposes, should anyone else want to see or know about these trailer skirts. Please feel free to add any additional comments on these if you have more info or an opinion on the usefulness of these skirts.

If you are wondering... this was my original description/question:

Anyone out there know the true purpose of these "skirts?" I noticed in the southern US many trucks had these, and I was wondering if it's for better fuel economy? or is it prevent vehicles (idiots in 4 wheelers) from getting under the trailer during an accident?

Either way, it reminds me of European trucks. I thought it was different so I filmed it, I've never seen them before. I think I saw some on a van trailer too.

I've only driven garbage trucks, so cut me some slack... lol :)