Breakdown of Seitdem der Unfall passiert ist, ist die Straße gesperrt worden.
sein
to be
passieren
to happen
der Unfall
the accident
die Straße
the street
Questions & Answers about Seitdem der Unfall passiert ist, ist die Straße gesperrt worden.
Why does the second half of the sentence use ist ... gesperrt worden?
This is the passive voice in the Perfekt (present perfect) tense. You form it with a conjugated form of sein (here, ist), the past participle of the main verb (gesperrt), and worden. It translates to 'has been closed off.'
Why do we use worden here instead of geworden?
worden is the past participle of werden. Normally, the past participle is geworden. But when it is used as a helping verb to form the passive voice in the Perfekt tense, it drops the ge- prefix and becomes just worden.
Why are there two ist verbs right next to each other across the comma?
This is due to German word order. Seitdem (since) starts a subordinate clause, pushing its verb (passiert ist) to the end before the comma. That whole first clause counts as 'position one' for the overall sentence. The main clause must put its verb in 'position two', so it starts immediately with ist right after the comma.
Why does passieren use sein (passiert ist) instead of haben?