What's the name of the highway entrance where you are?
"What's the name of the highway entrance where you are?"(あなたがいる高速道路の入り口の名前は何ですか?)と尋ねると良いでしょう。「highway entrance」は高速道路の入り口を表します。
他にも以下のような表現が使えます:
Can you tell me which highway entry point you're near?
What does the sign for the freeway on-ramp say?