Learn Farsi: بزرگراه‌ها به دلیل طوفان بسته شده است. - The highways have been closed due to the storm.

It uses the past participle of the main verb, بسته (closed), followed by the present perfect form of شدن (to become). The present perfect of شدن is its past participle شده plus the "to be" verb است. Together, بسته شده است literally means "is become closed," which translates to "has been closed."

Why does the verb بسته شده است end with است instead of a plural ending, since "highways" (بزرگراه‌ها) is plural?

In Farsi, inanimate plural subjects (things that are not alive, like highways) usually take a singular verb. So even though بزرگراه‌ها is plural, the verb uses the third-person singular ending است rather than the plural اند (which would make it بسته شده‌اند).

Can I just say بسته است instead of بسته شده است? What is the difference?

You can, but the meaning changes slightly. بسته است means "is closed" (simply describing the current state of the road). بسته شده است uses the passive voice to mean "has been closed" (emphasizing the action that recently happened to the road, causing its current state).

Does به دلیل طوفان require an ezafe (the short "e" connector)?

Yes, it is pronounced be dalil-e toufan. The phrase به دلیل means "for the reason of" or "due to," and it needs the to connect "reason" () to "storm" ().