 With this in mind, in 1957 the Riga Railroad Machinery Plant and the Dynamo Plant made a drastic redesign of the SN multiple units, producing 5 service prototypes of what would ultimately be known as the ER1 trainset.These were 10-car trains consisting of 5 2-car sections (each comprising 1 power car and 1 trailer), which were permanently coupled together.This greatly improved the power-to-weight ratio (hence improving acceleration) and simplified production; the disadvantage was that train length could no longer be adjusted for traffic conditions.