Complex sentence: IRT Division trains would have an unacceptably large gap between the platform and train if they were allowed in the BMT/IND Division, and BMT/IND trains would not fit in the IRT tunnels and stations.
Split into simpler sentences: IRT Division trains would have an unacceptably large gap between the platform and train if they were allowed in the BMT/IND Division. Likewise, BMT/IND trains would not fit in the IRT tunnels and stations.