A car manufacturer wants to change the content of a certain automobile to have less steel in order to get better gas mileage. One hundred standard cars and 100 cars of the new content are built and test driven across country to determine the overall gas mileage. This study is an

I would say that this study is an experiment.

The car manufacturer wants to test some changes that he wants to implement in his cars, which is why he has two control groups (standard cars and cars with the new content) to test those changes out. This is a typical experiment and not an observation as he is not really observing much.