Not be a nitpick but even if a crossover is put there, trains can't run on the Bway line since the stop arm is on the opposite side of the truck, a recipe for disaster.
Also, the originan part of the subway (Lower Lex, Upper 7 Av/Bway) can't handle them since the turns would be too sharp. The 42 St , maybe cuz that part is straight for the most part, except the TS end