No railway would be complete without coaches and trucks, and those appearing in the children's television series Thomas the Tank Engine and Friends are no exception. Coaches carry passengers, and trucks carry freight. In many episodes, coaches and/or trucks are key to the episode's plot line. The engines prefer coaches, which are smooth-running and well-behaved. The trucks, on the other hand, are nothing but trouble. In the words of Rev. W. Awdry: – from the story Thomas and the Trucks (The Railway Series, book 2: Thomas the Tank Engine).