In the early twentieth century, the line between Manchester London Road (now called Piccadilly station) and Stockport became unable to cope with the increasing traffic. To solve the problem, a new route avoiding Stockport was constructed by the London and North Western Railway; it ran from Slade Lane Junction, located in Longsight, to Wilmslow through what was then mainly a rural area. The primary purpose was to provide a bypass for express trains, but a few wooden stations were built on the line to encourage suburban development. In practice, very few expresses latterly used the line, as it was necessary for most trains to serve the important station at Stockport. The line opened in 1909 and, from 1923, was operated by the London Midland and Scottish Railway.

In the 1950s, as part of British Rail's Modernisation Plan, the British Transport Commission identified the Styal line as a suitable test track to prove its new electrification scheme; the line was electrified in 1959. Some of the stations were rebuilt using the Mod-X system at this time.^[5] Following the Styal line tests, it was decided to adopt the 25 kV system across the electrified Great Britain rail network, outside the Southern Region.^[6] There was a half-hourly electric service (Monday - Saturday) between Manchester Oxford Road and Alderley Edge, operated by Class 304 EMUs.^[7] Services were extended to Altrincham when the MSJAR was re-electrified at 25 kV AC in 1971 and operated in this way until the line between Altrincham and Manchester was transferred to Manchester Metrolink in 1990.

In the 1970s, the Styal line was included in a proposal to create an underground railway across Manchester City Centre. The Picc-Vic tunnel was planned to connect the two major mainline railway termini, Manchester Piccadilly and Manchester Victoria; it would have enabled Styal line trains to run directly across the city to Bolton and Bury. The Picc-Vic scheme was abandoned in 1977, due to funding difficulties.^[8]

In 1993, a short spur line to Manchester Airport was opened, branching away the Styal line between Heald Green and Styal. Initially, services ran via Heald Green only, until a triangular junction was added a few years later which provided a link towards Styal.^[9] Many services were then diesel powered until 2014. The introduction of Class 350s by First TransPennine Express on the Edinburgh-Manchester Airport line in December 2013 and Class 319s by Northern Rail in early 2015 curtailed the use of diesel trains on the line; this allowed for a 100 mph service compared with 75 mph limit for many diesel trains, such as the Class 156 and the now-retired Class 142 Pacer trains.^{[citation needed]}

In 2006, the platforms at Mauldeth Road, Burnage, East Didsbury and Gatley stations were all reconstructed, as well as access improvements at Heald Green; patronage on the line increased after this investment. At the time, most platforms were future-proofed and extended to allow six carriage operation; however, it was not until 2019, with the arrival of the Class 195 and Class 331 units, that this platform capacity was fully utilised on Northern routes to Liverpool (Mauldeth Road) and Blackpool North (Burnage, East Didsbury and Gatley) which operate with six coaches.^{[citation needed]}

In recent years, usage of the line has surged with growing commuter patronage, along with non-stopping services which use the line between Manchester Piccadilly and Manchester Airport. Nowadays, most services on the line operate via the airport. There are a couple of services each day (mainly long-distance trains) which take the direct route from Styal to Heald Green; that is to say, from Heald Green South Junction to Heald Green North Junction, for train crew route knowledge retention purposes northbound. However, the only services on the junction southbound are either freight or a Transport for Wales service which doesn't stop at either station and only operates on Sundays. This route can also be used for diversions if the Stockport route is closed for engineering work or is blocked due to an operational incident.^{[citation needed]}

Stopping services edit

All stations on the line are served by two stopping services per hour operated by Northern Trains: one runs between Liverpool Lime Street and Manchester Airport and the other runs between Manchester Piccadilly and Crewe. On Sundays, this is reduced to one train per hour which runs between Liverpool Lime Street and Wilmslow. These services are usually operated by a Class 323 electric multiple unit (EMU).

The busier stations (East Didsbury, Gatley and Heald Green) are served by an additional third express train every hour. Early morning, late evening and peak services sometimes make additional stops to provide additional services; for example, Gatley is served by a Blackpool North train at 07:43 on Sunday mornings.

Mauldeth Road, Burnage and Heald Green are served exclusively by Northern Trains.

East Didsbury is also served by Transport for Wales Rail and Gatley is also served by TransPennine Express services.^[11]

Express services edit

TransPennine Express run through services, via Manchester Piccadilly, from across the north of England; these include to Saltburn, via York and Leeds. Their trains also operate from Glasgow Central/Edinburgh Waverley (both two-hourly) via Preston and Manchester Piccadilly.^[12] These were operated by Class 185 diesel multiple units until December 2013, when they were replaced with Class 350 EMUs.^[13] which were transferred to London Northwestern Railway in 2020, following replacement by Class 397 EMUs.

Transport for Wales Rail run a limited weekday service from the Airport to Chester, as an extension of their route between North Wales and Manchester Piccadilly, using Class 175 units.^{[citation needed]}

• Airport Line (Manchester Metrolink); Metrolink tram line also serving Manchester Airport.

• Haywood, Russ (2009). Railways, Urban Development and Town Planning in Britain: 1948-2008. Ashgate Publishing, Ltd. ISBN 9780754673927. Retrieved 19 June 2018.

• Greater Manchester Strategic Rail Study Final Report June 2001