Learn Dutch: De mist was hevig, zodat wij de weg niet konden zien. - The fog was severe, so that we couldn't see the road.

The word zodat (so that) is a subordinating conjunction. Just like the word tenzij (unless) from this lesson, it introduces a subclause. In Dutch subclauses, all verbs are sent to the very end.

Since the verbs are at the end, how do I know whether to write konden zien or zien konden?

When you have a helper verb (like the past tense modal konden, meaning could) and an infinitive (zien, meaning to see) grouped at the end of a sentence, the conjugated helper verb usually comes first. While you might occasionally see them swapped in written Dutch, konden zien is the standard and safest order to learn.

Why is niet placed after de weg but before the verbs?

The word niet negates the action of seeing the road, and the rule is that niet comes after a specific direct object (like de weg). Because the subclause pushed all the verbs to the end of the sentence, niet stays in its normal position, which ends up being right in front of the verbs.

Is hevig the most common word to describe bad fog?