Tees Valley line

The section of line between Bishop Auckland and Albert Hill Junction, Darlington (prior to joining the East Coast Main Line), as well as the section between Oak Tree Junction, Dinsdale (near Middleton St. George) and Eaglescliffe, follow the original route of the Stockton and Darlington Railway (S&DR), which dates back to 1825. The 1825 S&DR route is rejoined north of Eaglescliffe and runs as far as Bowesfield Junction, Stockton.

The S&DR line from Bowesfield to Watson's Wharf on the Tees near Middlesbrough opened in 1830, and this was extended to Redcar in 1846. The extension to Saltburn opened in 1861 and the line towards Brotton and Loftus opened in 1872. The line beyond Loftus (now the freight-only line to Boulby Mine) was part of the Whitby, Redcar & Middlesbrough Union Railway, opened in 1883; it closed on 5 May 1958.

In March 2015, a 0.62 miles (1 km) 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.

Services on the Tees Valley Line are operated by three train operating companies:

• Northern Trains, with a half hourly service from Saltburn to Darlington, of which one train every hour extends to all stations on the Bishop Line through to Bishop Auckland. Additional services operate along the Tees Valley Line during the morning peak, with some journeys between Saltburn and Newcastle running along the East Coast Main Line, rather than the Durham Coast Line.
• TransPennine Express also operates along part of the Tees Valley Line, with hourly services from Redcar Central to Manchester Airport calling at Middlesbrough, Thornaby, Eaglescliffe, Yarm, Northallerton, York, Leeds, and Manchester Airport. Eaglescliffe was added as a call for the first time during the December 2024 timetable change. Three trains a day extend to/from Redcar Central to Saltburn.
• London North Eastern Railway operates a weekday return service from Middlesbrough to London King's Cross.

Predominantly, rolling stock on the Tees Valley Line consists of:

• Northern Trains operates Class 156 and Class 158 diesel multiple units (DMUs)
• TransPennine Express uses Class 185 DMUs
• London North Eastern Railway operates Class 800 bi-mode multiple units

Between 2019 and 2021, Class 156 and 158 units operating on the Tees Valley Line were refurbished, introducing free WiFi, power sockets, on-board passenger information displays and an interior refresh.

Class 185 units were refurbished as part of a £32 million investment, with the work being completed in 2018.

Class 142 Pacer DMUs formerly served the line on Northern services, until the early 2020s when they were withdrawn from passenger service.

The combined Bishop/Tees Valley Line route serves the following stations:

Least-used stations

In 2019, the Tees Valley Line was home to two of the country's least-used railway stations.

Redcar British Steel

In 2017-18, Redcar British Steel was the least-used station in Great Britain, with an estimated 40 passenger journeys made.

Prior to service suspension in December 2019, it was served by two trains during the morning peak and two during the evening peak.

Teesside Airport

In 2012-13 and 2013-14, Teesside Airport was the least-used station in the country, with just eight passenger journeys made in both periods.

It is currently served by a once-weekly parliamentary service; a Sunday service, commencing at Hartlepool, calls here before continuing through to Darlington.

In 2020/21, due to decreased travel throughout the COVID-19 pandemic, the station saw only two passenger journeys made. While remaining officially open, the station has seen its service suspended since May 2022, with the one operational platform condemned as unsafe. As a result, there were only 2 passengers in the year beginning April 2022.