Don’t if you can help it…it’s slow, depressing and a lot of the folk have no road sense and even less manners!!! 
Dom.:
skinhead:
The units got a towing hitch on the back, the steel will be ballast to get some weight on the drive axle.Why? Is he worried the tractor will tip forward onto his windscreen when he brakes?
I’ve never seen it before. A big lump of steel STRAPPED doesn’t inspire confidence, but should I assume then that it has a kingpin / that it’s specially designed?
So the ballast is left in the yard in case he goes out without a trailer… wha’s he do with it when he picks up a trailer then?
Image here: goo.gl/9ZaeN
Looks like Ballast to me, probably originally from some sort or plant machinery like has been said before with a pin and a couple of things for a fork lift to put it on and off added to it.
I used to work for a company that delivered new Trailers, we had a large lump of concrete that could be attached to the fifth wheel so we could deliver drawbar trailers using a tractor unit.
In my experience the thought of driving in London has always been worse than the reality. Just got to get on with it really.