This line operated the S-series electric multiple units (S standing for "Severnye Zheleznye Dorogi", or "Northern Railroad").

After World War II, the entire production was transferred to the Riga Railroad Machinery Plant, which continued producing these trainsets until 1958.

All of these had one common design flaw: the traction motors were mounted directly on the axles to simplify manufacture, which in turn limited maximum speed to 85 km/h.

In 1954, the Riga Railroad Machinery Plant built several prototype 3-car electric multiple units designated SN ("Severnaya Novaya", or "Northern New").

As stated in the previous section, there were many busy suburban railroads in the Soviet Union which required a faster and more powerful replacement for the obsolete S units, but also one which was compatible with the low passenger platforms used on these lines (which the ER1 could not accommodate).

The cars are coupled together with the SA3 coupler, which is standard on Soviet rolling stock and allows vertical movement of up to 100 mm.

To maximize passenger accommodation, almost all electrical equipment is mounted either on the roof (pantograph) or under the car floors (starting resistors, compressors, etc.)

All underfloor equipment is enclosed in cabinets with removable spring-latched access panels to protect it from blowing dust and snow.

Specifications (for a standard 10-car train): Overall length: 201.81 m Empty weight: 470-484 t Number of seats: up to 1050 Traction motor 1-hour rating: 4000 kW Tractive effort: up to 26,350 kilograms-force Maximum speed: 130 km/h (130 km/h (81 mph)) Acceleration up to 60 km/h (37 mph): 0.6-0.7 m/s2 (0.6–0.7 m/s2 (2.0–2.3 ft/s2)) Most of the cars' interior space is taken up by the passenger salon.

The majority of the floor space is occupied by bench seats, above which are mounted luggage shelves and coat hooks.

The automatic couplers and their shock absorbers are mounted on short spine beams at each end of the car.

The doors and wire conduits are made of aluminum, which helped to keep the weight down and resulted in the cars being only slightly heavier than those of the ER1.

The truck frame's longitudinal beams are reinforced in the middle to take the car's weight via the bolster and suspension springs.

The transverse beams have a complex shape to accommodate the traction motors (which are mounted entirely on the truck frame).

The leading truck of the driving trailer has brackets for mounting the cab signal receiver coils.

The latter had the following design changes: the springs were softer; the bolster was attached to the frame by means of 2 swing links with rubber/metallic elements; the weight of the car body was borne by the bolster only via the skid pads (on the earlier type, part of the weight was also borne by the central pivot).

The gearbox casing is mounted on the axle by means of a sealed roller bearing, and is also attached to the truck frame via a special suspension.

The first such joint was fitted to an ER2 in 1964 as an experiment; in late 1965, five more prototypes with rubber couplings were built, and from 1966 onward these became standard on all new ER2s.

The wheels of the trailer cars are smaller in size (only 95 cm in diameter), solid, have shorter hubs and a thinner axle.

To coast, the engineer moves the controller handle to 0; this opens the line contactors, thereby shutting off all power to the traction motors, and moves the controller into starting notch #1 (therefore if the traction motors are turned on again, they are connected in series and all the starting resistances are in the circuit).

The traction motors are mounted on the truck frames (see above), which protects them from impact when rolling over rail joints and reduces the train's unsprung weight.

In the 1960s, the Riga Electric Machinery Plant developed a new type of traction motor, the URT-110, which had similar performance to the DK-106B.

Electricity from the overhead contact wire is picked up by the train through pantographs mounted on the roofs of the power cars.

In 1965 due to installation of more stable pantograph isolators (made of plexi glass AG-4), the relay system developed by N. A. Lapin was excluded from trains' construction.

In 1966-1975 period the railcar manufacturing plant of Riga continued the release of ER2 suburban electric trainsets, for 3000 V DC.

The body is supported on beam over the amortizers, equipped by rubber dowel, through edge sliders; while ____ serves only for transmitting horizontal forces.

Traction engine rotor is connected with a gear train through the rigid clutch (rubber cord shell).

In case of automatic starting controller's shaft is turned to a next position, and the current in electric engine is brought down to 170 to 180 amperes.

They consist of bicollector voltage divider (dynamotor) for EK-7A motor compressors which need 1500 V, and current generator for control circuits, lighting, etc.

They were intended to improve interior, exterior outlook, as well as passengers' and crew's comfort, particularly, the shape of engineer's cab, the installation of other pantographs, as well as some other machinery.