Complex sentence: Thus, moving the B to the Brighton Line meant it would only need to be operated on weekdays, while the D could now provide 24-hour service to both the Concourse Line in the Bronx and the West End Line in Brooklyn.
Split into simpler sentences: Thus, moving the B to the Brighton Line meant it would only need to be operated on weekdays. In contrast, the D could now provide 24-hour service to both the Concourse Line in the Bronx and the West End Line in Brooklyn.