The right jolly driver is surrounded by his right jolly mates. (That's mates in the British sense.) And they have every reason to be jolly.
Why, they have a road, a means of hauling and being hauled, and they have Agricon, "the only conference dedicated to those working within the Agricultural, Foods, Tipping, Milk and Livestock sectors of today’s road transport industry."
Naturally, the ebullient sow has pride of place (she gets the passenger seat instead of steerage), but all of the animals are, you know, haulage. Cargo. Goods. Stuff. Just this side of inanimate. Don't let the smiles fool you—these things are barely alive.
And that's what they're smiling about!
You see, in a strict, class-based society like England's, there's a certain comfort in knowing one's place. It offers some a security denied them by too much potential. The Road Haulage Association provides the livestock all the lack-of-potential they could ever wish for.