Although the Joban Line and the Keihanshin Local Line were taken into account in designing type 103 cars, it was generally believed that some amendments might be required when they were actually put into service.
103系電車を設計した時には常磐線や京阪神緩行線は想定線区に入っていたが、実際に投入するに際しては何らかの手直し等が必要との認識をしていた。