2 is better than 3 as the active voice version of 1 because "They" in 3 has no antecedent.
Both 5 and 6 are passives for 4 since there is no "by ___" in 4.
Since 4 is in past tense, either present perfect or past perfect will make sense in 5 and 6.
1. The street is closed for construction.
2. The city has closed the street for construction.
3. They have closed the street for construction.
(What is the suitable active voice of #1?)
4. The door was shut.
5. He had shut the door.
6. They had shut the door.
(Which one is the passive voice of #4? Which subject is suitable as the subject in the active voice? Do we have to use the structure "had p.p." here?)
3 answers
Numbers one and four are not in active voice; they are passive. The subject is the road or the door. It just is whatever it is, closed or shut. In active voice, it is the city or "they" or "he" who did the action in closing the street or the door.
Reed is right. Sentences 5 and 6 are the active voice versions of 4.