1 is a true statement, conditional on the Post Office maintaining it
2 is not a statement. It's a command, an imperative, a "bossy" type sentence that does not make a statement about any facts. There may not be any oncoming traffic and you the reader may not even drive.
3 is a false statement, unconditionally false. It's a contradiction. A disjunctive where both disjuncts are always false Unless you're using some different number system.
4 is a true statement, but conditional on which Millard Fillmore you mean. there may be other Millard Fillmores that were never a US president.
