Transportation facilities are well-improved.
Is this a correct sentence?
I don't know if the word well-improved can be used in this sentence.
If something can be improved, it can be improved to a degree, and it stands to reason that it can be "well improved" as well.
That said, it sounds a bit awkward to use that formulation in English, except perhaps in specific circumstances where the verb improve had already been established and probably repeated. In most cases you can get by simply with improved. To advance beyond that degree you might have to say the thing had been "greatly improved" (or similar) to sound natural.