 Since the mid-1960s, the ER2 has been the most widely used type of suburban train in the Soviet Union and its successor states.Electric multiple units were first used in the Soviet Union in 1926 on the Baku-Sabuncu segment of the Baku mainline.These consisted of 2-car or 3-car sections, each of which had 1 power car and 1 or 2 trailer cars (a similar consist to that still used today).