Valmet Nr I

Nr I
An Nr I class tram at Hakaniemi in Helsinki
In service	1973 – present
Manufacturer	Valmet
Built at	Valmet airplane factory, Tampere
Constructed	1973–75
Entered service	1973
Refurbishment	1993–2003 (1st modernisation) 2005 onwards (2nd modernisation)
Number built	40
Number in service	40
Fleet numbers	31–70
Capacity	39 passenger seats 106 standing places
Operator(s)	Helsinki City Transport (HKL)
Line(s) served	All HKL tram lines
Specifications
Car length	20.10 m (65.9 ft)
Width	2.3 m (7.5 ft)
Height	3.7 m (12 ft) with pantograph
Floor height	approximately 0.91 m (3 ft)
Maximum speed	60 km/h (37 mph)
Weight	28 tonnes
Traction system	2× Strömberg GHCU / H6232 of 130 kW (170 hp)
Power output	260 kW (350 hp)
Braking system(s)	track/disc/electric
Track gauge	1,000 mm (3 ft 3 3⁄8 in)

Nr I is a class of articulated six-axle (B′2′B′ wheel arrangement), chopper-driven tram operated by Helsinki City Transport on the Helsinki tram network. All trams of this type were built by the Finnish metal industry corporation Valmet between the years 1973 and 1975.

Between 1993 and 2004 all trams in the class were modernised by HKL and redesignated as Nr I+ class. Currently HKL classifies them as NRV I.

Nr I were the first type of articulated tram operated by the HKL. The design of the Nr I type trams was based on the GT6 type trams built by Düwag for various cities in western Europe since 1956, but the Nr I incorporated several technological innovations that had not been available when the GT6 was designed. The Nr I trams were delivered by Valmet between 1973 and 1975, with the first seven trams delivered in 1973, further 18 delivered in 1974 and the final 15 in 1975. As the first mass-produced tram type in the world, the Nr I featured thyristor chopper control. The first tram of this class entered revenue-earning service on 16 December 1973 on line 10. Although the trams of this type are numbered 31 to 70, the first unit was not the 31st tram to be used by the HKL. The HKL tram numbering system had been reset in 1959, with the numbering of new trams delivered that year beginning from 1.

In the early 80s the city of Gothenburg, the forerunner in creation of modern light rail systems in Europe, wished to purchase Nr I -based trams from Valmet for its own tram network. However, due to pressure from the Swedish government, Göteborgs spårvägar were forced to place an order with the Swedish ASEA instead. In Helsinki a further developed version of the Nr I, the Nr II class, was delivered by Valmet for HKL between 1983 and 1987. The Nr II class trams have an identical external appearance and very similar interior layout to the Nr I class.