In an episode (supposedly) devoted to the environment, Jeremy Clarkson investigates the controversial M4 bus lane while Richard Hammond reviews the Saab 9-3 from the least environmentally friendly place imaginable — a traffic jam. Elsewhere, Jeremy discovers how to drive a Lotus Elise 111S properly, Richard launches the search for Britain's fastest faith, and Jason Dawe visits a school to settle the important question of which supercar children love most. Rick Parfitt is the Star in a Reasonably Priced Car.