# North Downs Line

The North Downs Line is a railway line in South East England. It runs for 45 miles 40 chains (73.2 km) from Reading in Berkshire to Redhill in Surrey. It is named after the North Downs, a range of chalk hills that runs parallel to the eastern part of the route. The name was introduced in 1989 by Network SouthEast, the then operator. The North Downs Line serves the settlements in the Blackwater Valley as well as the towns of Guildford, Dorking and Reigate. It acts as an orbital route around the south-west of London and has direct connections to the Great Western Main Line at Reading, the Waterloo–Reading line at Wokingham, the Alton line at Ash, the Portsmouth Direct line at Guildford and the Brighton Main Line at Redhill.
Three different operators run passenger services on the North Downs Line. Great Western Railway runs services along the entire length of the line from Reading to Redhill, the majority of which continue along the Brighton Main Line to Gatwick Airport. Southern trains between Reigate and London Victoria use a 1 mi 67 ch (3.0 km) section west of Redhill. South Western Railway services between the capital and Reading use the line west of Wokingham and the same company operates between Guildford and Ash en route to Aldershot.
The majority of the North Downs Line was constructed by the independent Reading, Reigate and Guildford Railway company (RG&RR), although the section between Guildford and Ash Junction was built by the London and South Western Railway. The line opened in 1849 and services were run from the outset by the South Eastern Railway, which took over the RG&RR in 1852. Three sections of the line were electrified by the Southern Railway in the 1930s although around 29 route miles (47 km) remain unelectrified. In the early 21st century, infrastructure works to increase the capacity of the line were undertaken, including the provision of new platforms at Reading and Redhill.

## Route
### Overview

The North Downs Line is a 45-mile-40-chain (73.2 km) railway line in South East England. It links Reading railway station on the Great Western Main Line in Berkshire to Redhill on the Brighton Main Line in Surrey. It serves the settlements in the Blackwater Valley on the borders of Hampshire, Surrey and Berkshire, as well as the Surrey towns of Guildford, Dorking and Reigate. It acts as an orbital route bypassing the south-west of London and has direct connections to the Waterloo–Reading line at Wokingham, the Alton line at Ash and the Portsmouth Direct line at Guildford. The 2015 "Surrey Rail Strategy" noted that 56% of passengers on the route connect to services on other railway lines and that a quarter of journeys either start or end at Reading. Around 13% of passengers travel to or from Gatwick Airport.
The name "North Downs Line" was first used in 1989 by Network SouthEast, the then operator of the line. Between Redhill and Ash, the line runs roughly parallel with the North Downs, a range of chalk hills that runs from Farnham to the White Cliffs of Dover. Between Ash and Reading, the line crosses the sands, gravels and clays of the London Basin. The steepest gradients, 1 in 96, and the summit of the line are near Gomshall, where the route crosses the watershed between the Rivers Mole and Wey in Surrey. The distances along the line between Redhill (22 miles 40 chains) and Shalford Junction (41 mi 60 ch), and between Ash Junction (48 mi 34 ch) and Reading (68 mi 68 ch) are measured from Charing Cross station in London.
The North Downs Line is double track for the entirety of its 45 mi 40 ch (73.2 km) length and has a maximum operational line speed of 70 mph (110 km/h) for passenger trains. Three sections of the line, Redhill–Reigate, Guildford–Aldershot South Junction and Wokingham–Reading, are electrified using the 750 V DC third-rail system. Two sections, Reigate–Shalford Junction and Aldershot South Junction–Wokingham, together totalling 29 route miles (47 km), are unelectrified. The line has a W6 loading gauge, and overnight engineering possessions of up to 4+1⁄2 hours are available. In 2006, Network Rail classified the North Downs Line as "congested", but, following the construction of new infrastructure, this status was revoked in 2023.

### Reading to Guildford

The Reading to Guildford section of the North Downs Line is 25 mi 41 ch (41.1 km) in length and has 13 stations in total. Reading and Guildford stations are managed by Network Rail and have 15 and 7 operational platforms respectively. The other 11 stations have two platforms each. Earley, Winnersh Triangle, Winnersh, Wokingham, Ash and Wanborough stations are managed by South Western Railway (SWR). Crowthorne, Sandhurst, Blackwater, Farnborough North and North Camp stations are managed by Great Western Railway (GWR). The passenger train services that use this section of the North Downs Line are:
* Reading to Redhill and Gatwick Airport, operated by GWR using Class 165 and Class 166 units
* Reading to London Waterloo, operated by SWR using Class 458 and Class 455 units
* Farnham and Aldershot to Guildford, operated by SWR using Class 450 units
West of Wokingham Junction and east of Aldershot South Junction, this part of the line is electrified using the 750 V DC third-rail system, leaving an 11 mi 71 ch (19.1 km) unelectrified central section. Most services on the North Downs Line use platforms 4, 5 and 6 at Reading station, but access to other platforms is possible. The Reading station area is controlled from Thames Valley rail operating centre, the line from Earley to North Camp is controlled by Basingstoke rail operating centre, and the section from North Camp is controlled by Guildford signal box. The majority of this section has a line speed of 70 mph (110 km/h) with the exception of the approaches to Reading, Wokingham and Guildford stations, and a 40 mph (64 km/h) restriction at Ash Junction where the line curves sharply. The steepest gradient, to the west of Guildford, is 1 in 100.
The Waterloo–Reading line diverges from this part of the North Downs Line at Wokingham Junction, and a spur to the Alton line joins at Aldershot South Junction. In addition, the line passes beneath the South Western Main Line at Farnborough, but there is no longer a junction between the two. This section passes over two navigable waterways, the River Kennet and the Basingstoke Canal, as well as the unnavigable River Loddon and its tributary, the Blackwater.
Stations between Reading and Guildford (ordered from west to east) :
| Station | Mileage | Number of platforms | Managing company | Trains operated by | Opening date | Original name |
| Reading | 68 mi 68 ch (110.8 km) from Charing Cross via Redhill | 15 | Network Rail | GWR SWR CrossCountry Elizabeth line | 30 March 1840 | |
| Earley | 66 mi 1 ch (106.2 km) from Charing Cross via Redhill | 2 | SWR | SWR | 1 November 1863 | |
| Winnersh Triangle | 64 mi 72 ch (104.4 km) from Charing Cross via Redhill | 2 | SWR | SWR | 12 May 1986 | |
| Winnersh | 64 mi 10 ch (103.2 km) from Charing Cross via Redhill | 2 | SWR | SWR GWR | 1 January 1910 | Sindlesham and Hurst |
| Wokingham | 62 mi 13 ch (100.0 km) from Charing Cross via Redhill | 2 | SWR | SWR GWR | 4 July 1849 | |
| Crowthorne | 58 mi 66 ch (94.7 km) from Charing Cross via Redhill | 2 | GWR | GWR | 29 January 1859 | Wellington College |
| Sandhurst | 57 mi 22 ch (92.2 km) from Charing Cross via Redhill | 2 | GWR | GWR | 4 May 1852 | |
| Blackwater | 55 mi 58 ch (89.7 km) from Charing Cross via Redhill | 2 | GWR | GWR | 4 July 1849 | |
| Farnborough North | 53 mi 16 ch (85.6 km) from Charing Cross via Redhill | 2 | GWR | GWR | 4 July 1849 | Farnborough |
| North Camp | 51 mi 18 ch (82.4 km) from Charing Cross via Redhill | 2 | GWR | GWR | August 1857 | |
| Ash | 49 mi 18 ch (79.2 km) from Charing Cross via Redhill | 2 | SWR | SWR GWR | 20 August 1849 | |
| Wanborough | 34 mi 29 ch (55.3 km) from London Waterloo via Woking | 2 | SWR | SWR GWR | 1 September 1891 | |
| Guildford | 30 mi 27 ch (48.8 km) from London Waterloo via Woking | 7 | Network Rail | SWR GWR | 5 May 1845 | |

### Shalford Junction to Redhill

Between Guildford and Shalford Junction, GWR trains use the Portsmouth Direct line to travel between the two parts of the North Downs Line. The route passes through two tunnels, Guildford Chalk Tunnel and St Catherine's Tunnel. Reversible working is available on the down line on this section of track.
The Shalford Junction to Redhill section of the North Downs Line is 19 mi 79 ch (32.2 km) long and has eight stations in total. Reigate and Redhill stations are managed by Southern, but the remaining six stations (Shalford, Chilworth, Gomshall, Dorking West, Dorking Deepdene and Betchworth) are managed by GWR. Redhill has four platforms, but the other seven stations have two each. The passenger train services that use this section of the North Downs Line are:
* Reading to Redhill and Gatwick Airport, operated by GWR
* Reigate to London Victoria via Redhill, operated by Southern
Much of this part of the North Downs Line runs immediately to the south of the North Downs escarpment, although the route deviates to the south between Chilworth and Gomshall to avoid Albury Park. Only the 1 mi 67 ch (3.0 km) section between Reigate and Redhill is electrified. Between Shalford Junction and Gomshall, the line is controlled from Guildford signal box and the majority of the route to the east is controlled by Reigate signal box. Redhill railway station and its approaches are controlled by Three Bridges rail operations centre. The maximum speed on this part of the North Downs Line is 70 mph (110 km/h).
The route crosses the Mole Valley Line immediately to the east of Dorking Deepdene, but there is no longer a junction between the two. The navigable River Wey is crossed at Shalford via a steel truss bridge, which replaced the original wooden bridge in 1902. The North Downs Line crosses the River Mole on a five-arch, brick viaduct, built when the line was constructed in the late 1840s. The A24 dual carriageway at Dorking is crossed on a steel bridge, installed in 1964.
Stations between Shalford Junction and Redhill (ordered from west to east) :
| Station | Mileage from Charing Cross via Redhill | Number of platforms | Managing company | Trains operated by | Opening date | Original name |
| Shalford | 41 mi 2 ch (66.0 km) | 2 | GWR | GWR | 20 August 1849 | |
| Chilworth | 39 mi 15 ch (63.1 km) | 2 | GWR | GWR | 20 August 1849 | |
| Gomshall | 35 mi 21 ch (56.7 km) | 2 | GWR | GWR | 20 August 1849 | |
| Dorking West | 30 mi 42 ch (49.1 km) | 2 | GWR | GWR | 4 July 1849 | Dorking |
| Dorking Deepdene | 29 mi 65 ch (48.0 km) | 2 | GWR | GWR | February 1851 | Box Hill and Leatherhead Road |
| Betchworth | 27 mi 17 ch (43.8 km) | 2 | GWR | GWR | 4 July 1849 | |
| Reigate | 24 mi 27 ch (39.2 km) | 2 | Southern | Southern GWR | 4 July 1849 | |
| Redhill | 22 mi 40 ch (36.2 km) | 4 | Southern | Southern Thameslink GWR | 26 May 1842 (relocated 15 April 1844) | Reigate |

## History
### Proposal and authorisation

The Reading, Guildford and Reigate Railway company (RG&RR) was formed in August 1845. It was led initially by Frederick Mangles, a banker from Guildford, and most of the board members were businessmen from London and Surrey. The company's stated objective was to build a line linking the three towns in its name to "secure through traffic passing between the West, North and Midlands and the Channel Ports avoiding the congestion of London and thus saving time, distance and expense."
The engineer, Francis Giles, was commissioned to survey the line. His route, presented to the board in January 1846, had an estimated cost of £710,000 (equivalent to £86.85 million in 2023) and was to be double track throughout. It would run from the Great Western Main Line at Reading to the Brighton Main Line at Reigate Junction (later Redhill). Between Dorking and Gomshall, Giles's route required the use of the proposed London & Portsmouth Direct Atmospheric Railway. The approaches to Guildford would use part of the London and South Western Railway (LSWR) lines to Godalming and Alton.
Negotiations with other railway companies began at the start of 1846. By mid-January, the RG&RR had bought out the rival Reading and Reigate Company, promoted by David Mocatta, which had proposed a line with similar aims. That March, it agreed terms to run over the LSWR tracks from Shalford Junction to Guildford. In the same month, the South Eastern Railway (SER), which had wanted to build its own short branch from Reigate Junction to Dorking, offered to operate the line. A bill was prepared for Parliament and the RG&RR was authorised on 16 July 1846, the same day that the LSWR's line from Guildford to Alton was approved. The act gave the RG&RR the powers to construct the section of the line from Dorking to Gomshall, if it was not built in time by the London & Portsmouth Direct Atmospheric Railway Company.

### Route alterations and construction

Francis Giles died in March 1847 and his position as surveyor and engineer was taken, on a temporary basis, by Robert Stephenson. Stephenson began to make changes to Giles's scheme, primarily to reduce costs. Around £3000 was to be saved by simplifying the link to the South Western Main Line at Farnborough, eliminating the north–west curve, leaving only the north–east curve to be built. At Reading, Giles had proposed running alongside the Great Western Main Line on a widened embankment, but Stephenson argued that the RG&RR should build a separate station (later known as Reading Southern) instead of sharing the Great Western Railway (GWR) facilities. Minor alterations were also made to the route in the Gomshall, Albury and Ash areas. A deviations bill was submitted to Parliament and was given royal assent on 22 July 1847.
A formal ceremony to mark the start of construction took place near Betchworth on 20 August 1847. Contracts were awarded to George Wythes and William Jackson for the construction of the Reigate Junction-Dorking and Farnborough-Reading sections. In mid-1848, the plans for the London & Portsmouth Direct Atmospheric Railway were abandoned and the contract to build the Dorking-Shalford Junction section of the RG&RR was awarded to Charles Henfrey that May. The SER was responsible for constructing the stations on the eastern half of the line, for which it was paid £25,000.
Peter Barlow was appointed engineer in late 1847, although the exact date is uncertain. He disagreed strongly with Stephenson's alterations to the station arrangement at Reading but was unable to persuade the RG&RR board to reinstate Giles's original scheme. Barlow made some minor alterations to reduce costs, including reducing the span of the bridge over the Basingstoke Canal from 40 ft (12 m) to 24 ft (7.3 m). He also suggested building the Dorking to Farnborough section as single track, but the board decided to continue with Giles's plans for a fully double-tracked railway. Following the conclusion of negotiations with the LSWR, a bill authorising the curve linking the RG&RR to the South West Main Line at Farnborough was granted royal assent on 26 June 1849.

### Opening

Two sections of the line, from Farnborough to Reading and from Reigate Junction to Dorking, opened on 4 July 1849. Locomotives and rolling stock were delivered to the western section via the single-track link to the South West Main Line. From the outset, the line was worked by the SER. The initial timetable was four trains in each direction per day between Farnborough and Reading. There were seven trains from Dorking to London on weekdays and one fewer in the opposite direction.
The sections from Dorking to Shalford and from Guildford to Farnborough opened in August 1849. The collapse of St Catherine's Tunnel delayed the completion of the LSWR-constructed Shalford Junction to Guildford section, which finally opened on 15 October 1849. The initial daily full-line timetable included six trains from London to Reading, with five in the opposite direction, supplemented with an early morning departure from Guildford to the capital and an equivalent mid-evening return.
During the construction of the line, the RG&RR was unsure how best to serve the villages of Shere and Gomshall. When passenger services on the section between Dorking and Shalford began in August 1849, two temporary stations opened – one for each village. The Shere Heath station was closed the following year, and a permanent station was built at Gomshall to replace the temporary platforms there. In 1851, a platform was opened at the point where the line crosses the Dorking-London road. Initially called Box Hill and now known as Dorking Deepdene, the new station was intended to cater to passengers from the Leatherhead area.
The first freight trains began running on the line in September 1850. Goods sheds opened at Gomshall and Betchworth the following year, and a shed was provided at Ash from 1856. The yard at Dorking, equipped with an 8-ton crane and cattle pens, served both the town and the Denbies estate.

### Purchase by the SER and late 19th century

In October 1851, the SER applied to Parliament to take over the RG&RR. The purchase took effect in March 1852, although the authorising act was not given royal assent until 17 June 1852. Over the first few years of SER ownership, the financial performance of the line was poor. In 1855, the company stated that the line was losing £15,377 per annum (equivalent to £1.8 million in 2023), but the following year, the Railway Times estimated that the annual loss was around £30,000. Through trains from the GWR at Reading were introduced on 1 July 1863 with a daily Birkenhead to Dover return working, but disappointing passenger numbers resulted in the service being withdrawn in October 1868. In January 1869, there were five daily return services between Charing Cross and Reading, ten between Dorking and the capital, and one from Guildford. Passenger numbers from Dorking fell after the opening of the Leatherhead to Horsham line in 1867.
In the mid-1850s, Aldershot Military Town was established for the British Army in northeast Hampshire. In 1858, the SER opened North Camp station to serve the new camps. A goods yard was constructed at the station in 1859-60.
Several connections between the North Downs Line and other lines were created in the second half of the 19th century. The first was a 300 m (330 yd) single-track link running into the GWR station at Reading, which opened on 30 August 1855. The Staines, Wokingham and Woking Junction Railway (SW&WR), which had been granted running powers over the Wokingham-Reading section in 1853, opened its line from Ascot on 9 July 1856. A second link at Reading, which passed under the Great Western Main Line and which was owned by the GWR and SW&WR, was opened to goods services on 1 December 1858 and to passenger trains on 17 January the following year. At Dorking, a single-track west-to-south spur joining the Leatherhead-Horsham line, was opened on 1 May 1867 but closed around the end of the century. The fourth link, a tight curve to the Alton line allowing SER trains from Ash to run into Aldershot station, was completed in 1879.
The construction of the railway line from Godalming to Havant was completed in late 1858, although the first passenger services did not start running until January the following year. Since the line had been built on a speculative basis by the independent Portsmouth Railway (PR) company, it was unclear whether the LSWR would allow its trains to run over its line via Guildford and Woking to reach London. In July 1854, the PR gained authorisation to extend its line northwards from Godalming to Shalford, where it could join the North Downs Line. New embankments and a wooden trestle bridge across the River Wey were constructed by the SER to create a triangular junction at Shalford, providing an alternative route to the capital. However, before the link could be completed, the LSWR decided to allow PR trains to use its line, eliminating the immediate need for the connection. It is unclear whether track was ever laid over the spur, but the SER decided not to continue its work, fearing that completion would violate its long-standing agreement with the London, Brighton and South Coast Railway not to compete for traffic to Portsmouth.

### 20th century

As a result of the Railways Act 1921, the North Downs Line became part of the Southern Railway in 1923. Three parts of the line were electrified in the 1930s using the third-rail system. The 1.9 mi (3.1 km) section between Redhill and Reigate was electrified under the Brighton Main Line electrification programme. Electric trains began running in public service on 17 July 1932, with trains to and from Reigate splitting and joining at Redhill with trains to and from Three Bridges. The electrification of the Wokingham–Reading and Guildford–Ash sections was completed on 1 January 1939. One further development to take place in the 1930s was the withdrawal of the passenger service on the former LSWR line between Ash Junction and Farnham via Tongham on 4 July 1937. Freight services on this route continued until final closure in 1961.
During the Second World War, the North Downs Line was fortified with additional earthworks, tank traps and pillboxes. A nine-road marshalling yard was built at Shalford and the link to the Dorking–Horsham line at Dorking was reinstated. The North Downs Line played a major role in the transport of troops evacuated from Dunkirk in May and June 1940.
The first Beeching report, published in 1963, recommended shutting all stations between Shalford and Betchworth inclusive. Instead of the proposed partial closure, steam-hauled passenger trains were replaced by diesel multiple units in January 1965, although steam-hauled freight continued until the end of the decade. The final through services between London and Reading via Redhill (one train in each direction per day) were withdrawn at the same time. On 4 January that year, Class 206 units, nicknamed Tadpoles and officially designated 3R, began operating an hourly stopping service between Tonbridge and Reading, calling at all stations except Winnersh and Earley. The second Beeching report, which was published in February 1965, recommended that the whole of the North Downs Line should be developed as a trunk route for freight services.
Reading Southern station closed on 6 September 1965 and all North Downs Line services were diverted to platform 4a at the main Reading station thereafter. Platform 4b at Reading opened in May 1975. In November 1967, full-time staff were removed from all stations on the line, with the exception of Redhill, Guildford and Reading. The change was made possible with the introduction of conductor-guards, with the ability to sell tickets, on all trains. An express service between Gatwick Airport and Reading began in May 1980, calling at North Camp, Guildford and Redhill. These trains began stopping at Dorking Deepdene in May 1986.
From 1982, the North Downs Line came under the control of Network SouthEast, one of the five business sectors of British Rail. In 1989, groups of lines in the sector were given names and identities; the Reading–Tonbridge and Reading–Gatwick airport services were branded the "North Downs Line" and the crest of the former Tonbridge Urban District Council was applied to the trains. In 1993, the Class 165 and 166 units were introduced. The reaction to the new trains was positive and, over the following 12 months, a 46% increase in passenger numbers was recorded for North Camp. Tonbridge remained the easternmost terminus for the North Downs Line services until the electrification of the Redhill–Tonbridge line in 1994, when the stopping services were cut back to Redhill.

### 21st century

As the result of the privatisation of British Rail, the North Downs Line was included in the Thames Trains franchise, won by the Go-Ahead Group in 1996. The franchise was awarded to FirstGroup in 2003 and trains were branded "First Great Western Link" for the next two years. In 2006, the former Thames Trains operations became part of the Greater Western franchise, won by FirstGroup.
In the 2010s, additional platforms were opened at Reading, Redhill and Gatwick Airport stations, to increase capacity for trains using the North Downs Line and other passenger services. A major project to renew the signals in the Wokingham area and to transfer control of the northwestern part of the line to the Basingstoke rail operations centre was completed in February 2024.

## Passenger services and rolling stock
### Current

The main services on the North Downs Line are provided by GWR using Class 165 and Class 166 Networker Turbo diesel multiple units. There is a half-hourly service between Reading and Gatwick Airport via Guildford, with alternate services running semi-fast either side of Guildford. At Redhill, the Gatwick Airport services reverse to head south along the Brighton Main Line. A total of seven diesel multiple units is required to run the GWR Reading–Gatwick Airport service.
Services on the North Downs Line are provided by South Western Railway between Reading and Wokingham (trains to/from London Waterloo, operated by Class 458 and Class 455 units), and between Ash and Guildford (trains to/from Aldershot and Farnham operated by Class 450 units). Class 701 units are expected to start operating services between Waterloo and Reading in June 2025.
Southern operates frequent services using four-car electric multiple units between Reigate and London Victoria. These trains use the North Downs Line between Reigate and Redhill, where they join the Brighton Main Line.

### Former

The earliest locomotives to be used on the North Downs Line are thought to have been SER 2-4-0 engines, designed by James Cudworth. A Nasmyth and Gaskell 0-6-0 and a Hick 2-4-0 are known to have worked the line in the mid-1850s. E class 2-4-0 locomotives were introduced in the early 1860s and hauled passenger services until the end of the 19th century. James Stirling, who was appointed locomotive superintendent at the SER in 1878, introduced F class 4-4-0 engines to the line in 1897. From 1902, Q class 0-4-4T tank engines were used and are known to have worked the Ash-Aldershot shuttle services.
Traffic increased during the First World War, with additional trains serving the army camps at Aldershot. GWR 3300 class "Bulldogs" and 3252 class "Dukes" were deployed to the line, supplemented by 15 Great Northern Railway 2-4-0 locomotives. In 1924, Maunsell N class steam engines began hauling passenger trains, and P Class 0-6-0 tank engines took over the Ash-Aldershot shuttle at around the same time. In the 1930s, the majority of services were worked by F1 and D class 4-4-0s, and H class 0-4-4Ts. In 1938, ex-GWR 2-6-0 and 4-6-0 engines moved to the North Downs Line and continued to haul trains until the 1960s.
Traffic increased again during the Second World War. Between 27 May and 4 June 1940, troops evacuated from Dunkirk were transported via the line and civilian services were suspended to allow these trains to run. In the same year a new cross-country service between Newcastle and Ashford, Kent, primarily for military personnel, was introduced on the line. It ran until the end of 1944, when the southern terminus was changed to Southampton Docks.
In the 1950s, the majority of passenger trains were hauled by Maunsell N and U class locomotives, supplemented towards the end of the decade by Standard Class 4 tender and tank engines. From 1959 onwards, electrification schemes in Kent allowed LSWR N15 class "King Arthurs" and SR V class "Schools" steam engines to be transferred to the line. Class 33 diesel-electric locomotives began hauling trains in 1962. The final, scheduled, steam-hauled passenger service on the North Downs Line departed Reading Southern for Guildford on the evening of 3 January 1965, although a few steam-hauled freight services continued until the end of steam operation on the Southern Region in July 1967.
A new timetable was introduced on 4 January 1965, with 3R (Class 206) diesel-electric multiple units operating an hourly, all-stations service between Reading and Tonbridge. The new trains consisted of two 6S (Class 201) coaches from the Hastings Line coupled to an adapted 2-EPB driving trailer coach. As a result of the visible difference in width between the narrow Hastings Line stock and the standard-width trailer, the units were nicknamed Tadpoles. The Class 33 diesel locomotives, introduced to the line in 1962, continued to haul peak hour services until May 1977.
Three-car Class 119 units were introduced to the North Downs Line in April 1979 enabling the withdrawal of the Tadpoles in May 1981. The express service from Reading to Gatwick Airport was launched on 12 May 1980. The Class 119 units were especially modified for this service, and the buffet counter in the centre coach was removed to create extra luggage space. Initially the service called at North Camp, Guildford and Redhill, but it began stopping at Dorking Deepdene in May 1986. Three-car Class 101 units were later used on the route as well. The Class 119 and 101 units were replaced by Class 165 and 166 units in 1993.
Class 456 units were introduced to the North Downs Line on 23 March 2014, when they began operating between Ascot and Guildford via Aldershot. They were withdrawn from passenger service by SWR on 15 January 2022. In 2018, GWR announced that it would lease Class 769 hybrid multiple units for use on the North Downs Line and on other services in the Thames Valley. In 2022, the company decided not to pursue plans to introduce the Class 769 fleet and stated that all units were to be returned to the lessor.

## Freight services

The first goods trains began running on the North Downs Line in September 1850 and facilities for handling freight were provided at most stations. Goods sheds opened at Gomshall and Betchworth the following year, and a shed was provided at Ash from 1856. The yard at Dorking, equipped with an 8-ton crane and cattle pens, served both the town and the Denbies estate. The permanent goods yard at Reading Southern opened on 1 December 1858, replacing a temporary facility to the east that had opened with the line in 1849. The yard was used for goods services in February 1970. Most of the station yards on the line closed in the 1960s.
There were four major narrow-gauge railway systems linked to the line. The Chilworth gunpowder and cordite works, active until the end of the First World War, had an 800 mm (2 ft 7+1⁄2 in) railway. At Dorking West station, there was a British Timber Works narrow gauge railway, active between the 1910s and 1930s. Brockham Limeworks and Brickworks, to the east of Dorking, was connected to the North Downs Line by a standard-gauge siding but also had a small 2 ft (610 mm) system. Betchworth quarry and limeworks, which operated between 1865 and 1963, had an extensive system with four different track gauges.
The travelling post office train from Dover to Manchester Piccadilly via Tonbridge, Redhill, Guildford and Reading was routed along the line from May 1988 until 1996, when a new road and rail postal hub opened at Willesden. The Network Rail 2008 Strategic Business Plan recommended an enhancement project to enable freight traffic from the Channel Tunnel to use the line. In 2023, there were no regular scheduled freight services on the North Downs Line.

## Future

Three sections of the North Downs Line were electrified by the Southern Railway in the 1930s, but around 29 mi (47 km) remains unelectrified. There have been several proposals to either extend the electrified sections or to completely electrify the remainder. A study for Surrey County Council, published in two parts in 1995 and 1996, recommended that the Dorking–Reigate section be electrified and a north–east link from the Mole Valley Line be built, to enable a loop service to operate via Epsom, Redhill and East Croydon.
The "Surrey Rail Strategy", published in 2015, noted that infill electrification of the remaining unelectrified sections using the DC third-rail system would reduce the journey time between Reading and Gatwick Airport by 2+1⁄2 minutes for fast services and by 7 minutes for stopping trains. Overhead electrification of the line would reduce the journey time by 5 minutes for fast services and by 11 minutes for stopping trains. The following year, Surrey County Council suggested that electrification of the full length of the North Downs Line would create around 8,000 jobs and would stimulate £1.9 billion of economic growth, based on research by four local enterprise partnerships.
The "North Downs Line Traction Decarbonisation Strategy", published by Network Rail in 2024, evaluated the costs and benefits of completely electrifying the route. It noted that third-rail infill offered poor value for money and proposed that battery-powered electric trains should be procured when the Class 165 and 166 units are withdrawn. Whilst introducing a third train per hour between Reading and Redhill would allow stops to be removed from Reading–Gatwick services, it would deliver only a marginal improvement in the financial performance of the line.
The "Blackwater Valley Rail Survey", published in 1991, suggested replacing the station at Farnborough North with an interchange station where the South West Main Line crosses the North Downs Line. This option was dismissed in the 1995/6 Surrey County Council reports as it was thought that the stopping train frequencies on the two lines would be too low for suitable connections. The 1995/6 reports also proposed a new station at Park Barn to serve the Royal Surrey County Hospital and the University of Surrey. A local newspaper report in 2019, suggested that the new station, in northwest Guildford, could open in the mid-2020s. The 1995/6 Surrey County Council reports also suggested that the line could form the core of a rail link between Heathrow and Gatwick Airports.

## Accidents and incidents

* 19 June 1853: An SER passenger train from Reading to Reigate ran into the back of a Godalming-bound goods train in one of the tunnels south of Guildford.
* 12 September 1855: A light engine, which had departed from Reading, was misrouted into the path of a train from Charing Cross via Guildford and collided with it head on. Three passengers and the driver of the light engine were killed. One further passenger later died of their injuries.
* 17 January 1867: An LSWR passenger train from Alton ran into the back of an SER train from Reading about 300 yd (270 m) northwest of Guildford station. There were no fatalities.
* 18 January 1868: An SER train for Redhill derailed shortly after leaving Reigate, due to a landslip. The locomotive overturned, the first carriage was destroyed and the second carriage was slewed across the tracks. There were no fatalities.
* 8 September 1882: George White, a shunter employed by the SER, was struck and killed at Reigate by a non-stopping express train to London. He had been loading a horse into a horsebox attached to a Reading-bound train that had stopped at the station.
* 29 February 1892: Henry Wicks, a guard employed by the SER, was killed on the line between Chilworth and Gomshall. A coupling between two trucks broke and the rear portion, in which he was working, rolled backwards downhill at speed. He was thrown out of the guard's van and onto the embankment. A box hedge topiary, known as Jessie's Seat, has been cut in the shape of a pheasant as a memorial to Wicks.
* 9 November 1901: A fireman was run over and killed in thick fog by a non-stopping train at Blackwater, while attempting to extinguish a burning sleeper.
* 20 February 1904: A locomotive hauling a train carrying around 150 members of the Royal Northumberland Fusiliers, bound for service in Mauritius, derailed at Gomshall station. There were no fatalities, but three soldiers, the driver and fireman were severely injured. The accident occurred while the train was travelling at around 35 mph (56 km/h) and is thought to have been caused by a track defect.
* 11 April 1944: Two goods trains, one of which consisted of tankers of aviation fuel en route to airfields in Kent, collided at Shalford. The resulting fire damaged the steel road bridge over the railway.

## Listed buildings

There are three Grade II listed structures on the North Downs Line.
| Name | Location | Type | Completed | Date listed | Coordinates |
| Level Crossing cottage | Buckland, Surrey | cottage | 1848 | 18 August 1996 | 51°15′02″N 0°15′17″W﻿ / ﻿51.2505°N 0.2546°W﻿ / 51.2505; -0.2546 |
| Footbridge immediately south of Wokingham Station | Wokingham, Berkshire | footbridge | late 19th century | 16 June 1996 | 51°24′39″N 0°50′33″W﻿ / ﻿51.4109°N 0.8425°W﻿ / 51.4109; -0.8425 |
| Railway overbridge at NGR SU 7770 7109, Arbor Lane | Winnersh, Berkshire | rail bridge over road | 1848 | 28 April 1987 | 51°26′00″N 0°53′02″W﻿ / ﻿51.4333°N 0.8838°W﻿ / 51.4333; -0.8838 |