Complex sentence: They also allow for crossover between uptown and downtown trains on side platforms or a pair of island platforms, which is very useful when local tracks are closed for construction.Inside mezzanine's are fare control areas, where passengers physically pay their fare to enter the subway system.
Split into simpler sentences: They also allow for crossover between uptown and downtown trains on side platforms or a pair of island platforms, which is very useful when local tracks are closed for construction. Within the mezzanines are fare control areas, where passengers physically pay their fare to enter the subway system.