Pacer trains are railbuses built by British Rail between 1080 and 1987. There are several classes of them: 140, 141, 142, 143 and 144. They are diesel multiple unit trains, meaning each carriage has its own diesel engine. Pacers were built as a stopgap because British Rail did not have enough normal trains at the time and could not get new ones quickly enough. They were not supposed to be used for more than 20 years, but it actually took nearly 35 years to replace them.