Step-by-step explanation:
The grammatical name of the expression "which the driver have not dipped" is a relative clause. It functions as an adjective to modify the noun "headlights." The clause introduces additional information about the headlights and specifies that the driver has not dipped them. Specifically, the relative pronoun "which" refers back to the noun "headlights," and the verb phrase "have not dipped" describes the action that the driver has not taken. The overall function of the relative clause is to provide more detailed information about the noun it modifies.