Originally designed for the Munich S-Bahn, the Class 420 was judged in the mid-1970s to be unsuitable for the network[citation needed], mainly due to being uncomfortable and lacking on-board toilets.

[citation needed] Constructing an improved version of the 420 with the tentative designation Class 422 was discussed, but in 1978 the Deutsche Bundesbahn commissioned a batch of coaches from Duewag and MBB.

Among the design elements inherited from the recent LHB prototype carriages were the bogies with disc brakes and rubber airbag shock absorbers that also included automated level control, ensuring level boarding from S-Bahn platforms with a standard height of 96 cm regardless of varying passenger loading.

They had been designed for long-haul Intercity and limited-stop commuter train services with a maximum speed of 160 km/h (99 mph) and were not an ideal fit for rapid transit duty.

The Cologne S-Bahn section went into full operation in 2002 in conjunction with the opening of the Cologne-Frankfurt high speed line.

Starting in 2008, 84 units of Class 422 were introduced in the Ruhr area section and around Düsseldorf, replacing the x-Wagen loco-hauled trains.

These Alstom Coradia trains are operated by DB Regio NRW and offer on-board toilet facilities.

All trains of Rhine-Ruhr S-Bahn ran with the red DB livery except for the S7 and S28 trainsets which are painted in the colours of their respective operators.

Starting in December 2019, there will be major changes in the Ruhr area section of the network: The standard service pattern will be altered from a 20-minute to a 30-minute or 15-minute headway.

A number of tunnel sections were added to extend the S-Bahn to new high-density housing estates (e. g. Cologne-Chorweiler), to suburbs that had historically been villages (e. g. Dortmund-Lütgendortmund station) or the Dortmund university founded in 1968.