Single Electrified BG = up & down[bi-directional] trains plying with e-loco though 1 line only. Eg:- UJN-INDB, ANGL-CTC line .
Double Electrified BG = separate tracks for up & down[unidirectional] trains plying with e-loco through 2 lines. Eg:- DHN-MGS Grand Chord.
Single Diesel BG = up & down[bi-directional] trains plying with diesel-loco though 1 line only. Eg:- GHY-DBRT/DBRG line.
Double Diesel BG =separate tracks...
more... for up & down[unidirectional] trains plying with diesel-loco though 2 line. Eg:- MLDT-NJP