May 1958. In March 2015, a electrified siding was laid adjacent to the Tees Valley Line, just south of Heighington. This allows low-speed testing of the trains manufactured at the nearby Hitachi Rail plant at Newton Aycliffe, including TOPS classes 800, 801, 805, 807, 810 and 385. Least-used stations Prior to the suspension of services to Redcar British Steel in 2019, the Tees Valley Line was home to two of the country's least-used rail stations. Redcar British Steel In 2017-18, Redcar British Steel was the least-used station in Britain, with an estimated 40 passenger journeys made. Prior to service suspension in December 2019, Redcar British Steel was served by two trains during the morning peak (07:57 to Bishop Auckland & 08:25 to Saltburn), and two during the evening peak (16:58 to Middlesbrough & 18:17 to Saltburn). Teesside Airport In 2012–13 and 2013–14, Teesside Airport was the least-used station in the country, with just 8 passenger journeys made per year, in both periods. As of the December 2019 timetable change, Teesside Airport is currently served by a once-weekly parliamentary service. Currently, the single Sunday service, commencing at Hartlepool, is timetabled to call at Teesside Airport at 14:54, before continuing through to Darlington. Stations References External links GenMaps - Maps of Durham, Yorkshire 1885 NPEMaps - Maps of area circa 1950 Network Rail maps of Route 9 - North East Routes North Eastern Railway Tour 2000 Communigate - Grangetown streets and buildings The Bishop Line Railway lines in North East England Rail transport in County Durham Rail transport in North Yorkshire Transport in Middlesbrough Community railway lines in England