Line 51 (Amsterdam Metro)

M51, also known as the Ring Line, is an Amsterdam Metro line running from Amsterdam Centraal station to Isolatorweg metro station, almost creating a full circle through Amsterdam. It was opened in December 1990 as a metro/tram hybrid line named sneltram (express tram) and served the suburb of Amstelveen. Using special rolling stock, the Amstelveen Line ran as a metro on 750 V DC third rail from Amsterdam Centraal to the Amsterdam Zuid station, where it would switch operation modes and utilize 600 V DC overhead lines and end at Poortwachter. An extension to Westwijk was completed in 2004. In Amstelveen, the line partially ran on the same track as tram line 5 and had many level crossings.

The express tram was the result of a compromise between the municipalities of Amsterdam and Amstelveen. A full metro line for the suburb was proposed in the original 1968 plan of the system along with three other lines throughout the city, but the majority of these lines were cancelled due to protests against the demolition of houses caused by the metro construction in the city centre of Amsterdam. Amstelveen still wished to continue with the plans for a metro as it would not require any demolition, but the topic was too controversial in Amsterdam. The Amstelveen Line had problems following its opening as it suffered from a lack of capacity due to the lack of trains. It was temporarily shortened from Centraal to Zuid for 7 months in February 1991. Many collisions occurred at the level crossings, leading to additional safety measures.

Studies in the 2000s showed that Line 51 was unreliable due to the switching of operation modes, its level crossings and because it ran alongside a regular tram line. It was proposed to upgrade the section in Amstelveen to a full metro line as part of the new North–South Line, but this was deemed to be too expensive and was made impossible due to the developments at Zuid. In 2015, it was decided to convert the line into a high-quality and low-floor tram. Line 51 got its current route on the Ring Line as a full metro in March 2019 and was replaced by tram line 25 in Amstelveen.

Initial plan
The Bureau Stadsspoor (City Rail Bureau) was formed in 1963 and concluded that Amsterdam needed a new rail system to move large numbers of people. The bureau released five reports by 1966 and laid out a final plan for a total of four metro lines in the city, which was presented to the public in the same year during a press conference by alderman Roel de Wit. The plan included a North–South line originating in Amsterdam-Noord, which would split into two branches in the suburb of Amstelveen and end in Schiphol-East. In May 1968, the municipal council of Amsterdam approved the plans based on the advice of the bureau and reserved the money required for the first phase of the project, the two East–West lines. Construction of the first lines commenced in August 1970 at Weesperplein.

The metro was a controversial topic as the houses above the underground sections of lines in the city centre of Amsterdam had to be demolished to make construction possible. This caused protests against the metro at Nieuwmarkt in 1975, which eventually led to the cancellation of all other lines in the plan, while the two East–West lines already under construction were scaled back to just the eastern part of the city and renamed as the East Line. The reputation of the word "Metro" in Amsterdam was damaged for a long time due to the entire incident.

Planning and construction
The area where the lines were supposed to be installed was undeveloped despite the cancellation in 1975. In 1978, the municipality of Amstelveen announced that it would not take a metro line into account anymore, but that it was positive about a sneltram ("high-speed tram" or "express tram"). This was the result of a compromise between the municipalities of Amstelveen and Amsterdam; Amstelveen initially wanted a full metro, while this was still politically controversial in Amsterdam. In the summer of 1979, both municipalities announced their support for an express tram line from Amsterdam Zuid station to Amstelveen with 13 stations. In September, the municipality of Amstelveen unexpectedly voted against the line, leading to more discussions. Amstelveen opposed because they claimed the tram line would not be faster or an improvement over the busses already running, and asked for more frequent busses instead. In November, the Ministry of Transport and Water Management announced that it would only support the express tram if it was extended to Amsterdam Centraal station instead of ending at Zuid, resulting in less transfers.

In February 1985, the two municipalities agreed on building the express tram; funding from the Dutch Government was secured shortly after. The GVB would financially compensate Centraal Nederland, which ran a bus route from Centraal station to Amstelveen. Centraal Nederland still started a campaign to construct a dedicated bus lane instead, which they claimed would be cheaper than the tram. Despite this, the municipality of Amstelveen voted in favour of the express tram over the bus lane in August 1985. The line was expected to cost 130 million Dutch guilder, with the government paying 54 million guilder and the municipality of Amsterdam funding the rest. The line was named Amstelveenlijn (Amstelveen Line) and was expected to be the first of multiple express tram lines around Amsterdam. Construction on the line started in August 1987 and was met with protests by houseboat residents at Duivendrechtsevaart, who had to move out. Landscaping of the areas with dirt were complete by May 1988. The GVB started to test the new tram units in May 1990 on the line. A few weeks before the scheduled opening, two trains collided during a test run and were damaged, resulting in a reduced frequency at opening. The line officially opened on 30 November 1990. Metro and express tram lines were numbered in the 50s, with the Amstelveen Line receiving number 51. The line ran as a metro using the existing track of the East Line from Amsterdam Centraal to Amsterdam Zuid on 750 V DC third rail. After Zuid, the trains would extend their pantographs and pick up current from 600 V DC overhead lines to serve Amstelveen as a tram. The line used a tunnel beneath Amsterdam Zuid to join the Parnassusweg street. The second part of the route also shared tracks with tram line 5 and was constructed on the median strip of a road. This led to the line having 15 level crossings in the suburbs where the right of way was regulated by traffic lights, which is unusual for a metro line. Despite its metro/tram hybrid usage, the line was not called a metro due to the controversy surrounding the term. The platforms constructed in Amstelveen had a length of 65 m and were compatible for high-floor units. On stations where the express tram ran alongside regular trams, an additional platform for low-floor trams was built. Upon its opening, the line terminated at Poortwachter. There were plans to expand it to Westwijk by 1993 and later to Schiphol Airport or Uithoorn. The destination board on the trains already had the option of displaying "Westwijk" and "Schiphol-Oost" before the line opened.

Operation as hybrid
The GVB started to have problems with the line as soon as it opened. Within a week of the opening, 5 of the 13 units were out of order due to technical problems or repairs. The capacity of the remaining trains was not enough and some people were left behind on the platform during rush hours due to the vehicles being full. The route of the line was shorted from Centraal to Zuid in February 1991 as 11 of the units were not running due to technical problems caused by the winter. The line resumed service on its normal route 7 months later in September, with the tickets for the line initially being free as these were considered to be test runs. The tests ended and passengers were required to pay again by early November. Following the resumption of service, regular busses still ran just behind the express trams just to be sure in case a problem occurred, as the rolling stock was sensitive to problems when switching operation modes, electronics froze during cold days and some communication cables were chewed by rabbits. Despite the issues, the municipality considered the line to be "sufficient" and started discussions to build a new express tram line from Isolatorweg to Gein.

Residents of Buitenveldert started a campaign in October 1995 to increase the safety of the level crossings of the express tram after three people were killed in separate accidents within a month and many heavy accidents occurred. They found the precautions taken at crossings, consisting of just a flashing light, to be insufficient despite the trams passing at high speed through traffic and threatened to block the crossings with cars. The trams can go though crossings at a high speed as the traffic light immediately turns white—meaning proceed for public transit—when a tram is approaching, quickly leading to collisions when pedestrians, bikers or cars fail to stop at their red light. The GVB announced the next day that it would install fences and warning signs at some crossings. Following an investigation a week later, maximum speed on some crossings was limited to 40 km/h for the trams. An express tram caught fire at the Weesperplein station on 12 July 1999 due to a blocked disc brake. Although the tram was carrying no passengers at the time, the smoke coming from the fire caused all levels of the station to be evacuated. Two people were taken to hospital for smoke inhalation, but were discharged quickly after their injuries were determined to be minor. GVB installed barriers at four more level crossings on the line in 2003 after a high number of collisions. Around ten people died in collisions involving the express tram during its entire operation span. The extension of the line to Westwijk was completed in September 2004.

Discussions on conversion
According to a 2007 study by the municipality, the line regularly had reliability problems. These were mostly caused by the switching of operation modes, level crossings and because the line was partially running on the same track as a regular tram line. Since the express tram shared some of its route with regular metro lines, a disruption in Line 51 would cause a disruption in the other lines as well. The same study found that it was "essential" to upgrade the Amstelveen Line to modernise the metro system of Amsterdam. This would also impact the North–South Line (Line 52), already under construction at the time, which was set to terminate at Amsterdam Zuid, as the number of metro platforms at the station would limit the frequency of the line. The study proposed to shorten Line 51 by one stop, extend the North–South Line to Westwijk also as a metro/tram hybrid or to extend Line 52 to Amstelveen Stadshart (terminus of tram line 5) as a full metro and have Line 51 operate to Westwijk from there. An action plan to convert the line was completed in 2009 and was pending approval from the involved municipalities. The conversion was expected to cost 400 to 500 million euros and be completed by 2018.

A project office was founded in February 2010 to prepare and enable decision-making of the conversion of the line in 2012. A city development study in 2011, approved by the municipal council, also recommended to upgrade the line to a full metro as a part of the North–South Line. In early 2011, the first report on the possible conversion concluded that it would not be possible to complete and open the new Amstelveen Line in time for the North–South Line. In May, the committee started considering alternative options to a full conversion. The project office was dissolved in September 2011 by alderman Eric Wiebes. Wiebes had imposed a cost–benefit analysis which found that the upgrade to a full metro would be too expensive and unaffordable, while the office kept pushing for the conversion.

On 9 February 2012, the province of North Holland and the municipality of Amsterdam agreed to relocate approximately 1 km of the A10 motorway underground in a tunnel. The metro platforms at Amsterdam Zuid would be moved further west, resulting in the tunnel used by Line 51 becoming useless and making the extension of the North–South Line to Amstelveen impossible. On the same day, the municipalities of Amsterdam and Amstelveen announced their support for the conversion of the line into a high-quality tram costing around 300 million euros. In March 2013, the Amsterdam regional transport authority definitively determined the preferred option for Amstelveen, where a tram line from Amsterdam Zuid to Westwijk would replace Line 51 and tram line 5 would keep running. The transport authority made the decision to continue with this option in December 2015 after the two municipalities voted in favour of it in November. In December 2016, it was announced that the new tram line would be extended to Uithoorn. The contract to carry out the conversion, which was expected to start in early 2019, was given to VITAL in 2017.

Route change
The Amstelveen Line closed on 2 March 2019. Metro 51 kept its original route from Amsterdam Centraal to Zuid, and instead of branching off to Amstelveen, it continues west-bound and ends at Isolatorweg. Following this change, the line partially runs on the Ringlijn (Ring Line), which is also the nickname given to the line along with Line 50. Following the closure, high-level platforms in Amstelveen were removed to make way for low-floor platforms, four stations were closed and some level crossings were grade separated. The replacement of the Amstelveen Line, tram line 25, was opened on 13 December 2020. On 30 March 2020, the GVB temporarily suspended the metro 51 as a result of the COVID-19 pandemic in the Netherlands impacting the number of passengers; service was resumed on 29 April. The frequency of the line was halved in early 2022 due to a lack of staff. Line 51 was chosen as it ran alongside other lines on its entire route.

S1/S2
Consisting of two cars, the S1/S2 units are 30 m long and 2.65 m wide. The first 13 units (45–57) are named S1 while the 12 units (58–69) from an additional order are named S2. Two units can be coupled together for operation in Amstelveen, while four can run together in the rest of the system. The tram platforms in Amstelveen were built for the width of the trains, while stations on the rest of the system were compatible for a width of 3 m. The units were fitted with retractable footboards to bridge the platform gap in those stations. The trains can reach a maximum speed of 70 km/h.

Built by La Brugeoise et Nivelles (BN), 13 units of the type were ordered in 1988 only for use as Line 51. As the line was unusual, the trams were designed specifically for the GVB. In 1989, the municipality recalculated the number of trains needed to operate the line and came to the conclusion that an additional 12 units were needed. By the time the line opened, the ministry still had not allocated the required funding for the extra trains. The order was placed after funding was approved by the ministry in early 1991. There were problems with the retractable footboards caused by a design error. These were fixed by BN for free. GVB put the blame of the capacity and technical issues that occurred after the opening of the line on the constructor and considered asking for financial compensation. Two units arrived in 1993, while the remaining ten were delivered a year later. Capacity issues on the line were resolved following this as the trams started running coupled together in March 1994.

Express tram stock is expected to have a lifespan of 30 years or less given the complex operation required. By the 2010s, the units were considered to be prone to technical issues due to their age. Following the conversion of the express tram, the S1/S2 trains went for through a technical upgrade for the final time and were used on regular metro lines. The trains are set to go out of service by 2024 with the arrival of the newer M7 metros.

S3/M4
The S3/M4 units are 31 m long and 2.65 m wide. There are four S3 units (70–73) that can convert into an express tram and operate like the S1/S2, while the 33 M4 units (74–106) are solely in use as a metro on other lines with third rail pick up. Four units of the type can run coupled together, except in Amstelveen. The units were ordered in February 1994, to be built by Construcciones y Auxiliar de Ferrocarriles. BN had also made an offer to deliver new units, but was not selected due to regular problems with the previous express trams.

The S3/M4 units were bought for the new Line 50, the Ringlijn (Ring Line), which was initially also called an express tram line despite being a full metro line without any level crossings. The stations on this line were built for the width of the trains, leading to the S3/M4 units also being fitted with retractable footboards like the S1/S2 to bridge the platform gap in other stations of the system. One unit was sent to the Netherlands in April 1996 and returned to Spain following testing. Deliveries of the type for operations was started and completed in 1997. While the trains operate at a speed of 70 km/h, the units are technically capable of reaching 100 km/h. The S3/M4 trains are set to go out of service by 2027 with the arrival of the newer M7 metros.