The English term "car" has two definitions:
1 a vehicle with four wheels and an engine, that can carry a small number of passengers. In this meaning, "car" = 汽车。We say 一辆汽车,not 一节汽车。
2 (used in American English) a train carriage. In this meaning, "car" = 车厢。We say 一节车厢,not 一辆车厢。