EN57 (manufacturer's designation: Pafawag 5B/6B) is an electric multiple unit used by the Polish railway operator (PKP). It was built for suburban and long-distance services. Presently it is used by Przewozy Regionalne (Polregio), Łódzka Kolej Aglomeracyjna, SKM Trójmiasto, Koleje Dolnośląskie, Koleje Śląskie and Koleje Mazowieckie companies in Poland. History Designed for regional transport, class EN57 was based on the earlier class EW55 units. EW55 were the first electrical multiple units built in Poland with 100% domestic components. They were built by Pafawag works in Wrocław. Production started in 1962 and ended in 1993 with 1452 trainsets produced, many of which are still in operation. This class is believed to have had the longest production period in the world for electric multiple units. The first-generation units had first-class compartments, but units numbered 602 and upwards were produced with only second class. Due to very long production period, the series varies between specific production spans. Units up to number 1113 have corrugated sides and three windscreens, units numbered 1114 to 1825 (second-generation) have flat sides and three windscreens, whilst units from number 1900 up to 1953 (third-generation) have flat sides and two windscreens, resembling class EW58 units. Classes EN71, ED72, and ED73 units were based on class EN57. SKM Trójmiasto which operates service in the Tricity area uses these units and has also modernised them, mostly to the interior. As a result of several fires and accidents, units numbered 201 to 206 were assembled from surviving cars of previously destroyed units. Since 2006, many EN57 units have been modernised with funding from the European Union. The changes affect the appearance of the units, with the ends being redesigned. The interior was also changed, and air-conditioning retrofit was done on many of said modernisations. Mechanical and electric devices remain mostly unchanged. Modified units are being renumbered from 2001 upwards. Technical data EN57 is a three-car electric multiple unit with traction motors located in the middle car. The unit has four LK450 motors, each with power of 145 kW. The outer two cars are both driving trailers and do not have motors. Trailers are distinguished with letters a and b, with part a including compressor and part b including the batteries. Each part of the unit consists of three compartments, divided by corridors. In the trailers only two compartments are for passenger accommodation, while the third was thought to be luggage compartment. In the