On subway networks, they have also become more common, as evidenced by the Nuremberg U-Bahn whose 1970s first generation VAG Class DT1 do not have them but whose VAG Class DT3 of the 2000s and 2010s and VAG Class G1 of the 2020s come equipped with automatic gap fillers.
Subway networks are increasingly incorporating automatic gap fillers, exemplified by the Nuremberg U-Bahn's evolution of train cars. The early DT1 models (1970s) lacked these features, while later generations like the DT3 (2000s/2010s) and G1 (2020s) have automatic gap fillers.