OVERGROUND 1970. Northern Heights Underground History. Photographs of the abandoned 'Northern Heights' railway. This railway ran from Finsbury Park via Stroud Green and Crouch End to Highgate, with a branch from Highgate via Cranley Gardens and Muswell Hill to Alexandra Palace. The gradient of the line caused problems for locomotives from the outset, resulting in unreliability. London Transport had planned to take over the line, running tube trains along it instead of steam engines, but although these works were advanced, they were disrupted by the second world war and ultimately abandoned.