The Hertford loop line (also known colloquially as the Hertford Loop) is a branch of the East Coast Main Line, part of the Northern City Line commuter route to London for Hertford and other Hertfordshire towns and an occasional diversion route for the main line. The line is part of the Network Rail Strategic Route 8, SRS 08.03 and is classified as a London and South East Commuter line.

History

The line was opened in three stages between 1871 and 1924. The first section called the Enfield Branch Railway was developed by the London and York Railway and went from Wood Green to Enfield. In 1898, a plan was approved to extend the line north to Hertford and Stevenage, in order to relieve congestion on the main line without having to widen the Welwyn Viaduct. Work started in 1905 and Cuffley was reached on 4 April 1910. The construction of two major viaducts and the Ponsbourne Tunnel (at 2684 yd, the longest in the eastern counties of England and the last to be built by traditional methods), combined with World War I shortages of men and materials, delayed the opening of the route to Stevenage until 4 March 1918. Then it was single track and for goods services only. The line finally opened to passengers on 2 June 1924 when a new station at Hertford North was opened. The line was electrified in 1977. The line was also used frequently during the Second World War as the Welwyn/Digswell Viaduct was at high risk from bombs.

Route and settlements served

The Hertford Line leaves the East Coast Main Line at Langley Junction, just south of Stevenage. It rejoins the East Coast Main Line at Wood Green South Junction, north of Alexandra Palace.

Operations

Great Northern operates suburban services along the Hertford Line between London King's Cross or Moorgate, and Stevenage, Watton-at-Stone or Hertford North. Occasionally, London North Eastern Railway, Hull Trains, Grand Central, Lumo, Thameslink and other faster Great Northern services operate non-stop along the route when diverted off the main section of the East Coast Main Line, due to incidents or planned engineering work. There is a reversing siding to the north of Bowes Park which is occasionally used to reverse London North Eastern Railway trains heading for Bounds Green Depot. There are also bay platforms at Hertford North, Stevenage, and Gordon Hill, the latter acting as a terminus during peak hours and night only.

Infrastructure

The line is about 24 mi long, is double track throughout and is electrified at 25 kV AC using overhead line equipment. It has a loading gauge of W9 and a maximum line speed of 75 mph. Grade-separated junctions connect each end of the northbound track with the main line. All stations are long enough to accept two three-car (20m) EMUs. Not all stations are long enough for newly introduced 6-car EMUs, but their walk-through design allows for access.

Tunnels and viaducts

Major civil engineering structures on the Hertford Line include the following.

ERTMS trials on the Hertford loop line

Network Rail used Beacon Rail owned Class 313 unit 313121 as a test vehicle for ERTMS on the Hertford Line. The plan involved resignalling a 5+1/2 mi section of the double track route to allow existing passenger and freight services to work bi-directionally over the up Hertford loop line, freeing the down line for ERTMS tests and evaluation.