Complex sentence: All the platforms are split into two sections, a and b, allowing two services to occupy a platform at the same time however platforms 1 and 4 are rarely used in this manner except when a train divides.
Split into simpler sentences: All the platforms are split into two sections, a and b, allowing two services to occupy a platform at the same time. Platforms 1 and 4 are, however, rarely used in this manner except when a train divides.