Keep Left...

I've sat here all day and night long,
Telling everyone right from wrong,
I know what's in and what's out,
You can tell from my whereabouts,

I'd been sitting alone for a while,
Then this truck came along with smile,
With his big white bulk,
I'll make him sulk,
As I send him into single file.

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Big nod to he who inspired this and whom from clues picked up, is aiming to do something similar.