tractor with 2 5th wheels

I can't see the pic but I'm assuming it's a daycab and probably Yellow. There is a system that allows a truck to connect the dolly to the rear of the truck frame and run it as part of the truck. The first fifth wheel slides up to be out of the way while running it in this conficguration. When you pull doubles you unhook the dolly and slide the first fifth wheel back into place.

 

What caught my eye was the tread, or lack of, on the rear tires.

 

Is this the one, RT?

http://www.thetruckersreport.com/truckingindustryforum/yrc/68860-jiffing-101-for-yellow-guys.html

 

You know I never understood why companies would pay extra for that either unless they use the extra axle on the tractor to haul hevier trailers when not pulling doubles.

 

we use these dollies still, the frame is narrow, it has two heavy alignment pins, and are air ride. I dont like them because you cant see them behind the front trailer when backing them to hook the set.

 

Yup, thats what its for and how its done.