Learn Farsi: شاید او خواب‌آلود پشت فرمان چرت می‌زده باشد! - Maybe he is dozing off behind the wheel while drowsy!

Because the action of dozing off is seen as an ongoing process happening right at this moment. The word shâyad requires a subjunctive form to show uncertainty. If we used the present subjunctive chort bezanad, it would mean maybe he will doze off in the future. The continuous form emphasizes that he might be dozing off right now, built with mi- plus the past participle zade plus bâshad.

How does the word khâb-âlud work in this sentence, and what does its suffix mean?

It acts as an adverb describing his physical state while driving, translating to while drowsy. The noun khâb means sleep, and the suffix -âlud means tainted with or full of. You will also see this useful suffix in other descriptive words like gard-âlud (dusty) or khun-âlud (bloody).

Does the continuous subjunctive conjugation apply to both parts of the compound verb chort zadan?

No, in Persian compound verbs, only the light verb is conjugated. The non-verbal portion, chort (a nap or doze), remains completely unchanged at the front. The continuous subjunctive only changes the light verb zadan into mi-zade bâshad, resulting in the final phrase chort mi-zade bâshad.

Is posht-e farmân a direct translation of the English idiom behind the wheel?

Yes! The word means steering wheel in the context of vehicles, though it can also mean a command or order. Just like in English, (literally behind the steering wheel) is the natural, everyday way to express that someone is actively driving a car.