Railway, Hull Trains, Grand Central 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 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 the 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 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 . 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 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. References Hornby, Frank (1995) London Commuter Lines. Volume 1: Main lines north of the Thames. Kettering: Silver Link Publishing Ltd. Rail transport in Hertfordshire Railway lines opened in 1871 Railway lines in London Railway loop lines Railway lines in the East of England Standard gauge railways in England Transport in the London Borough of Enfield Transport in the London Borough of Haringey