I guess it depends on who you hold by. From a summary I found:
“An important question arises whether driving in a car is considered Yichud. Rav Moshe (Teshuvot Igrot Moshe 4:65:3) rules that one should do his best to avoid driving a car alone with another woman even during the day on well-traveled roads. He reasons that although one is not secluded when driving, he can readily find a relatively private place alongside the road. Thus, since one has such easy access to sin when driving a car, Rav Moshe rues that driving alone with a woman in a car should be avoided except in case of great need. Rav Shlomo Zalman Auerbach appears to adopt the same approach in his Teshuvot Minchat Shlomo 1:91:21.
However, this makes dating in most circumstances quite difficult if not impossible. In fact, many Poskim disagree with Rav Moshe and rule that traveling alone in a car with another woman does not constitute Yichud unless one is driving in a very remote area or at a time when there are very few cars on the road. These authorities include Rav Mordechai Eliyahu (the former Sephardic chief rabbi of Israel who is a highly regarded Posek in many circles in Israel, cited in Techumin 10:311), Rav Aharon Lichtenstein (in a Shiur delivered to students of Yeshivat Har Etzion), and Rav Mordechai Willig (in a Shiur delivered at Yeshiva University).