Apart from being cheap to make, what’s the point of celebrity travelogues? Stars on free holidays that we’re supposed to find fascinating. But don’t.

It’s Michael Palin’s fault, of course. He invented a genre and did it so well that imagination-free TV channels have been desperately trying to copy him ever since.

Steven Fry driving round the USA in a London taxi. Why? Sue Perkins does the Mekong River. Eh? Fast Show duo John Thomson and Simon Day go gaucho in Argentina. Ludicrous.

But every now and then along comes a programme that almost makes all the bad ones worthwhile. Like ITV’s highly watchable Billy Connolly’s Tracks Across America.

Chronicling the Scottish comic’s epic 6000-mile train journey through 26 states, this is a thoroughly enjoyable three-part series.

Fans will be sadly aware that the Big Yin has had his troubles lately. But, as always, he can see the funny side.

“As you probably know,” he giggled. “I’ve got Parkinson’s Disease. People with Parkinson’s Disease shouldn’t have showers on a train. In much the same way Vietnam veterans shouldn’t go to firework displays in swamps. I nearly broke my neck!”

Setting off on his odyssey, Billy climbed aboard at Chicago and headed for Minnesota, its 27million acres of corn and its legendary State Fair, which dates back to 1859.

Sometimes factsheets can be fun. Take it away Mr C: “Two million people gather to eat 27miles of foot long hot dogs, 20million cookies and all manner of meatballs.” Still riding high in the deadly sins charts… gluttony.

Next stop North Dakota where self-confessed hippy Billy visited a forlorn oil town that’s gone bust and worried about fracking.

And after bonding with an obsessive Elvis fan in the familiar sounding Montana town of Glasgow the delighted host stood listening to a yodelling cowboy as a massive freight train trundled by right on cue. Stunning footage.

“That really happened,” he declared. “Me, a cowboy yodeller and a train in Montana. Someone up there must like me.”

Deeply moved by Seattle’s tent city for the homeless, the idealist funnyman was rather too determined to insist he’d found heaven on earth.

No matter how many times he was told otherwise, he hailed this canvas community to be a nirvana-like triumph. “Human beings at their very best,” he gushed. If so, I’d hate to see them at their very worst.

But hey, it’s his show and he’s doing it his way. Traversing God’s own land by rail is an inspired idea. You don’t find much out about a country when it’s 30,000ft below you.