SM53
SM53, originally designed MBO and colloquially known as Høka, were a class of 58 trams and 50 trailers built by Høka and Hägglund for Oslo Sporveier. The units were used on the Norway's Oslo Tramway from 1952 until 2000. The long and wide trams weighed. They had four motors providing a combined power output of, allowing for a top speed of.
The first series of thirty trams in 1950, with delivery in 1952 and 1953. These were designated MBO50. The next order was for new bodies for used Class SS units. The eight motor units were designated MO and nicknamed Chickens, while the twelve trailers were designated TO. These twin-axle units proved unsuccessful and Oslo Sporveier therefore took deliver of more MBO units. The next batch of twelve MBO55 units were delivered in 1957 and the final batch of eight were designated MBO56 and delivered in 1958. These were built for use on the Lambertseter Line, but were found unsuitable for use on light rail service and later moved back to the streets. From 1985 to 1991 eleven units were rebuilt with new cabs, interior and fronts, and designated SM83. Retirement of the class started in 1980 with Chickens. The series were gradually replaced, with the last SM53 units being taken out of service in 1997. The last SM83 were taken out of use in 2000.
History
Order and original series
At the end of the Second World War Oslo Sporveier had a fleet of 331 trams, of which only the 46 Gullfisk trams were modern bogie-constructions. The remaining were twin-axle and limited in capacity. Oslo Sporveier needed more and newer matériel and considered several options. More Gullfisk were considered, but their aluminum bodies were found to be unsuitable, they had issues with cracks in the bogies and their electrical system was prone to faults. They were design with entrance through the middle door, which had during the high usage during the war proven to be inefficient and often led to two conductors being needed for each car. By then flow-through units with a stationary conductor had become common. There were also significant developments within controllers and 300-volt motors. As such additional orders for Gullfisk were discarded.File:Høka under bygging 2.jpg|thumb|left|Construction of an original batch of trams at Høka in Hønefoss in 1952
An invitation for tenders was issued in 1947. Ateliers de Constructions Electriques de Charleroi offered to build a European adoption of the PCC streetcar, although the necessary licenses for Scandinavia were held by Svenska Järnvägsverkstäderna. The trams met all of Oslo Sporveier's demands, except their high power usage. However, the downside was the high price and that foreign production would require currency exchange licenses, which could be complicated because part of the price was for royalties.
The second offer came from Strømmens Værksted and Norsk Elektrisk & Brown Boveri, for an enlarged model of the Class 1947 being built for the Bergen Tramway. It was a variant of a standardized tram built by Brown, Boveri & Cie. for the Swiss tram market. The final offer was from Hägglund and Høka for a variant of Hägglund's Mustang. These were in various versions being delivered to the tramways in Stockholm, Gothenburg and Malmö.
File:MBO 204 Storokrysset.jpg|thumb|Tram 204 serving the Kjelsås Line at the intersection at Storo in 1978
Oslo Sporveier opted for Høka and Hägglund's bid and in 1950 signed an agreement to buy thirty motorized units with delivery in 1952, at 250,000 Norwegian krone per unit. Høka held the Norwegian rights to a Czechoslovak patent for wooden-filled steel profiles that Hägglund used in its design. The bodies were therefore built by Høka in Hønefoss, while Hägglund built the electrical and mechanical components. Final assembly was carried out by Hägglund and Oslo Sporveier at Sagene Depot in Oslo. The first tram arrived in Oslo on 1 September 1952 and, after final assembly and tests, entered revenue service on 11 November 1952.
The trams were first used on Line 13, which ran from the Sagene Line via Stortorvet to the Kjelsås Line. Half the original series was delivered by April 1953, allowing other lines to also use the new trams. The final tram of the original delivery series entered service on 14 December 1953. Upon delivery the trams had some issues with the controller. Upon occasion they would move to full speed or full brake without being activated by the motorman, causing a few minor accidents. It turned out that this was caused by a combination of mechanical weakness and user errors.
"Chickens"
The original plan was to copy a concept from Stockholm, where the trams were run fast and frequently without trailers. However, Oslo Sporveier soon decided to prioritize operating costs and instead run trams and trailers. At first the company operated Class SS trailers, but these proved unsuitable in combination with the MBOs. Oslo Sporveier was not willing to pay the price for new trailers and therefore chose a combination whereby new bodies were built atop existing undercarriages. Two such contractions were built at Sagene Depot in 1953, designated TO52 and the first unit came into revenue service on 23 November. A major issue with the trailers were doors which would not shut properly, often resulting with the trams running with open doors.Oslo Sporveier was considering the need for new trams, but were concerned because of the new trams having costs about twice the price of a Gullfisk. This led them into the idea of converting older trams by keeping the most costly parts, such as motors and wheelsets. However, the trams would receive new and larger bodies and interior. The company approved that twenty units be built, stipulating that fifty would be converted should it prove successful. Of the initial order, twelve were to be built as trailers and eight as motorized trams. They received new controllers and new braking system, and were largely rebuilt from Class U and Class SS units. The motorized version was designated MO52. They quickly received the nickname Chickens, as a pun of being smaller than units built at Hønefoss. The trailers were nicknamed Stiffsleds.
The first Chicken, no. 33, was met with dissatisfaction by the employees. They were built without air brakes, which meant that the conductor would have to traverse a full tram to reach the emergency brake should the motorman fall unconscious. The railway authorities sided with the employees, requiring the company to rebuild the unit. A similar concern was raised concerning the trailers. As air brakes are fail safe, the trailers would automatically brake should the trailer become disconnected. With the need for pressurized air system in place, the advantages of pneumatic door were reaped. However, the pneumatics systems largely ate up the costs savings of rebuilding material. Most of the work was carried out at Sagene Depot, and was carried out between mid-1954 to 1958.
The Chickens were used on a limited number of routes, from 4 July 1954 on lines 0, 8 and 13, variously serving the Vippetangen Line, the Grünerløkka–Torshov Line, the Sagene Line and the Sinsen Line. From 1955 they also started running on the Rodeløkka Line. The TO trailers were usually run with the Chickens, although they were also hauled by the larger Høka units. The tramway experienced that the Chickens did not have sufficient pneumatic capacity to keep a tram and trailer stationary while stopped on slopes, as separate compressors in the trailers were not installed. This made operating trailers with the Chickens a safety hazard and soon they were only seen in solitude.
Suburban prologue
The Oslo Metro was approved of by the city council in 1951. It would consist of a common, underground section in the city center and above-ground lines in the suburbs. It was soon evident that one of the suburban lines, the Lambertseter Line, would be completed in the order of magnitude of a decade before it could be hooked to the Common Tunnel. A similar situation was true for the Østensjø Line, which had been completed as a tramway in 1923. Oslo Sporveier was therefore given the task of operating the lines as tramways until the metro could open. The company considered building additional MO and TO units and move the new bogie trams to the suburban lines, but the poor performance of the rebuilt units soon made the company change its mind.Although Oslo Sporveier was determined to buy bogie trams, it considered options other than additional MBOs. A derivative of Stockholm's A24 was considered, as was a modernized Gullfisk with Vickers motors and two variations of Hägglund trams. The company considered multiple-unit trams, which would allow for faster speeds, but opted against this due to an increased fault rate and higher maintenance. A trial with the Gullfisk proved that it had low acceleration and speed and was shaking violently at high speeds, and the option was discarded. The company had two final options, additional MBO units or Vickers-based multiple units with bodies built by Hägglund and Høka, and motors from NEBB.
The tender was issued in 1953 for twelve trams and thirty trailers. Høka and Hägglund won the bid. All motorized units would be manufactured by Høka, along with twelve trailers. The remaining eighteen trailers would be built by Strømmens Verksted, due to lack of capacity at Høka. Each trailer cost 190,000 kroner, while the motor units cost 317,500. The contract included an option for eight more motorized units—which was quickly redeemed. Deliveries started in 1956 and the first trailer was put into revenue service on 28 May and the trailer class designated TBO55. The motor units, designated MBO55, first entered service on 15 July 1957, for the opening of the Lambertseter Line. A second batch was delivered from May through December 1958 and was designated MBO56. The total value of the SM53 series trams was 30 million krone. A single Mustang B25 trailer was bought used from Stockholm in 1957, when the trams there were closed. The trailer had left-hand drive, but by simply running it "backwards" the doors were placed on the right side. It was numbered 581 and classified as STBO50.
MBO55 and -56 also had issues with the controllers and the lubrication of the gear boxes, and the issues were soon corrected. The most troubling issue was a swaying motion when running on the suburban Vignoles rails. The riders complained to no avail until several derailments made the management aware of the severity. A Gullfisk was test-run and found to have a much smoother ride. A horizontal suspension was added, which helped somewhat to reduce the swaying. This could only be installed on the newer MBO55 and -56 series, as MBO50 had a different bogie design. The issue was never corrected in a satisfactory way.
File:Lambertseterbanen 4.jpg|thumb|left|For a year between 1966 and 1967 the SM53 trams continued to run on the Østensjø Line, while the new T1000 trains of the Oslo Metro had taken over services on the Lambertseter Line.