Example sentence: "Cars were expected to stay under the speed limit."
Is "expected" used there as an action verb (combined with "were" as a helping verb) or as an adjective (combined with "were" as a being verb)?
Example sentence: "Cars were expected to stay under the speed limit."
Is "expected" used there as an action verb (combined with "were" as a helping verb) or as an adjective (combined with "were" as a being verb)?
It's a verb used in a passive construction. If it were an adjective, it would be possible to switch are for other verbs that allow complex-intransitive constructions such as seem, look, appear, prove, etc.
*Cars seem expected to stay under the speed limit.
*Cars look expected to stay under the speed limit.
*Cars appear expected to stay under the speed limit.
*Cars prove expected to stay under the speed limit.
Use in complex-transitives would also be possible.
Bob made [the cars] [easy to drive].
*Bob made [the cars] [expected to stay under the speed limit].
Use of degree modifiers very, pretty should be possible if it were an adjective.
*Cars were very expected to stay under the speed limit.
Expected can take degree modifiers that work for verbs.
Cars were somewhat expected to stay under the speed limit.
Cars were very much expected to stay under the speed limit.