Due to the electrification of the A line and the resulting vehicle shortage since December 2014 again series 420 trainsets are used. These are 15 units taken over from the S-Bahn Stuttgart, but due to the lack of regular train traffic, they can not run on the main line during rush hours. They therefore take over exclusively the amplifier services on the S 2 between Dachau and Altomünster as well as amplifier rides on the west branch of the S 4 line and the S 20 line. Currently planning the S-Bahn Munich and the Bavarian railway company, 20 to 30 other units from Stuttgart to Munich to match the rising numbers of passengers. These are to be equipped with the existing units with the Linienzugbeeinflussung in order to be able to drive in the trunk tunnel.