Complex sentence: Most stations are of a modular design dating back to the initial system, extended and improved with two side platforms, each with separate access from the street, and platform canopies, although few examples remain of the original, distinctive rounded roof design.
Split into simpler sentences: Most stations are of a modular design dating back to the initial system, extended and improved. This design has two side platforms, each with separate access from the street, and platform canopies, although few examples remain of the original, distinctive rounded roof design.