What was the name of a short story about aliens thinking cars are the dominant life form and the humans inside are their internal organs? I read it in the UK in the 1980s in English in a science fiction omnibus. That was the only story I remember.
I think you're recalling the Hitchhiker's Guide to the Galaxy.
In the past, Ford arrived on Earth thinking that cars were the dominant lifeform. Upon arriving, Ford stood in the middle of the road trying to greet a car, not aware that he was going to be killed in an accident.
He was then saved by a random passerby, Arthur Dent. This is how their friendship started.
When Arthur finally understands that Ford is an alien, they discuss the weird circumstances of how they met each other. This is how the topic is initially brought up, since the story of H2G2 begins when Ford has already been on the planet for a considerable amount of time (and is already best friends with Arthur)
Ford: Didn't you think it was strange I was trying to shake hands with a car?
Arthur: I assumed you were drunk.
Ford: I thought cars were the dominant lifeform. I was trying to introduce myself.
In the H2G2 movie, there is a scene where Ford's greeting of the car and Arthur's rescue are shown. Link to video
I'm not sure if the Hitchhiker's Guide series of books counts as an omnibus specifically, but it is a collection of stories.
It sounds like the poem "Southbound on the Freeway" by May Swenson. I remember reading this poem in high school in the early 90's.
Here's the text of the poem:
May Swenson - Southbound On The Freeway
A tourist came in from Orbitville,
parked in the air, and said:
The creatures of this star
are made of metal and glass.
Through the transparent parts
you can see their guts.
Their feet are round and roll
on diagrams--or long
with white lines.
They have four eyes.
The two in the back are red.
Sometimes you can see a 5-eyed
one, with a red eye turning
on the top of his head.
He must be special-
the others respect him,
and go slow,
when he passes, winding
among them from behind.
They all hiss as they glide,
like inches, down the marked
tapes. Those soft shapes,
the hard bodies--are they
their guts or their brains?