When a person is driving a car and hearing Qur'an (audiocassette/ Radio), he might come across Aayat-e-Sajda. Is it an obligation to perform Sujood?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If a person recites a verse of prostration while he is riding a car or on an animal, or hears it from someone else, and the reciter performs the prostration, then if he wants to perform the prostration of the recitation of the Quran, he may perform only by making gesture if he is on a journey. If he is riding in a car while he is in city and he wants to make the prostration, then it should be performed on the ground. This prostration is comparable to voluntary prayers.

Allah knows best.