Can someone explain this for me?

Port for extra set of axles.

 

I hauled containers for a few years and I've never seen one like that. I'm kinda curious myself ha

 

I'm guessing but you've never seen a ten axle truck?
I doubt all the axles are run through one set of lines..but I could be wrong.

 

The extra glad hand is used to release the suspension pins on stretch frame chassis. It makes a chassis frame capable of loading a 20,40 or 45ft container.
You disconnect your red line from tractor, put it onto the extra glad hand, apply air then pins release. Stretch or compress the chassis to correct length, then remove the gladhand and pins pop back into place. Rehook your glad hand to the normal red one, add air and away you go.

 

We have a CN tri-axle like that in Marion. It can go from 40' to 53'.

 

That's how our 20'-40' chassis work.....

 

You're wrong. One set runs them all. Just plug and play at the back where you pin them on.