Besig is an adjective meaning ‘busy’. When you describe something as busy, you pair the verb is with the adjective:
Die kruising is besig = ‘The intersection is busy.’
It is not a separate verb; it’s the be + adjective construction.
Time adverbials like in die oggend, in die middag, in die aand usually appear at the end of a neutral Afrikaans sentence. If you want to emphasize the time, you can front it, triggering the V2 word order:
In die oggend is die kruising voor die brug besig.
Replace the definite die with the indefinite ’n before kruising:
’n kruising voor die brug is besig in die oggend.
(The apostrophe marks the dropped vowel in the indefinite article.)