Complex sentence: In 1933, London's underground railways, tramway and bus operators were merged to form the London Passenger Transport Board, which became known as London Transport, and Harry Beck's diagrammatic tube map appeared for the first time.
Split into simpler sentences: In 1933, London's underground railways, tramway and bus operators were merged to form the London Passenger Transport Board, this becoming known as London Transport. In the same year Harry Beck's diagrammatic tube map appeared for the first time.