What is it?

A plastic barrel of "slippery stuff" to spray on the rail head for testing wheel slip/adhesion control systems. Not that there is only one unit behind the leading test unit, and that trailing unit is most likely in full dynamic brake mode for loading down the lead test unit.  

Of course it must be a recycling bin.  It is a "green" engine isn't it?

Ron

Moonshine?

Porta-potty?

Boy, you'd have to have good aim for that!  

The beginnings of a Thomas the Tank Engine paint scheme. Will it never end?

So's not to pollute, contaminating the area, used batteries are thrown in the pretty blue barrel, from the locomotive!!!
Ralph 

I thought it's where they kept the spare electrons...

Rusty

could be a nose to - kinda makes the front look like a robot face;

eyes are windshields

nose is the blue thing

mouth is the plow

Its a water barrel.

Green, and wet behind the ears, when it grows up, it wants to be a Great Northern steam train.

like Great Grandpa

Next week your going to want to know what the rake on the roof is for

 That would be a tribute to the favorite Great Grandpa, a Canadian!  

(GG-1, Brunswick!)  

neutron walked into a bar and ordered a drink.

he asked how much?

the bar tender said

"for you, no charge"!

Yet another "neutron" joke.  Do you know how many neutrons will need therapy after this onslaught?  Well, I, for one, think it's pitiful, how some feel it's completely fine to make jokes at another's expense.  And, I will not remain neutral in this matter, despite the fact that neutrons have none to speak of.  

Caution!:Don't put your lips on it!...