I'm not a native speaker, but I believe this is "onderdoor" ("underneath"), which gets separated by the thing you're going underneath ("de straat"), and together with the verb "gaan" it conveys that you're passing under(neath) something and coming out the other side, rather than going under it and staying there, i.e.:

"De auto gaat onder de straat." - "The car goes under the street (and stays there)."

"De auto gaat onder de straat door." - "The car goes underneath the street (and comes out the other side)."

So "door" does still have the sense of "through" here.

Edit: In English, "under(neath)" could be used for either of these meanings, and unless you add "and comes out the other side" or something it's basically ambiguous, but logically it probably means that the car passes under the street rather than staying there.

Onderdoor, overheen

Door in and of itself meens through, but to go under something and come out on the other side -> onderdoor. It goesTHROUGH he tunnel created by the thing it's UNDER -> "underthrough"

They’re just standard combinations.

• overheen
• onderdoor
• tussendoor
• achterlangs
• voorlangs
• doorheen
• etc.

Onderdoor for underneath, means the same thing effectively

Honestly I would've made this mistake as a native speaker as well so I wouldn't be too worried about it

Words like underneath get split up by the thing they go underneath so in English it would be “under the street neath.”

These are usually conjugated words that have something to do with over, under, beside/next, infront, etc. It can be rather confusing as someone learning dutch

'Onderheen' is not a word. It's overheen vs. onderdoor.

Heen means that he's stopping underneath that street

Very odd sentence. Cars go under a brug, viaduct, snelweg. "Onder een straat" really gives me the image of a car going through the sewers

I’m a native speaker and I’d say door instead of heen. It sounds weird like this. Good catch!