ULF – Ultra Low Floor tram

ULF (Ultra Low Floor) is the tram with the lowest entrance height in the world of 197 mm - so low that no platform is needed.Following the international invitation to tender, Siemens was awarded the contract to design tramcar vehicles with an entrance height lower than 200 mm and to supply, to begin with, a series of 150 vehicles in spring 2004. Siemens will deliver these tramcars between December 2006 and 2015. Both the customer Wiener Linien and its passengers  have been very satisfied with the previous series of 150 tramcars. Many improvements have been made to make the vehicle even more attractive.

General vehicle design

This new-generation vehicle was designed for the existing infrastructure at Wiener Linien and to meet increasingly challenging passenger demands: such as air conditioning and level passageways through the passenger compartment,passenger information systems, and facilities for persons with impaired mobility.

Two types of vehicle are being built: a short tram (24,210 mm) and a long tram (35,470 mm) that can carry 136and 207 persons at 4 pers/m², respectively. Newly designed plastic seats have been installed to improve hygiene and for fire protection reasons.

The ergonomically designed driver‘s cab is very spacious and air-conditioned. The master controller is integrated intothe driver‘s seat, enabling the driver tooperate the tram with maximum comfort.

An easily accessible wheelchair spaceis provided behind the driver‘s cab.A manually operated folding ramp isavailable for bridging any differencesin height between vehicle and platform. Passengers with baby carriages benefitfrom the very low entrance height andend-to-end low floor.

Another special feature of the new vehicleis the smoke and heat detection system. All information from the detectors is transmitted in realtime to the driver.The use of flame-resistant and incombustible materials completes the vehicle safety concept.


The carbody essentially comprises aseries of vehicle modules and portalrunning gear with driven and non-drivensingle wheels, which are radially controlledin curves. Each portal running gear supports one vehicle module and is coupled to the next module. The two front and end modules are connected.Thus, the front and end portals are hinge mounted in the body. The ULF modules are equipped with two suspension systemsin line with standard practice for rolling stock.

The primary suspension consists of bonded-rubber laminated springs. Longitudinal and lateral guidance is provided by the column-guide principle used in bogies. The wheels are of the resilient type with rubber inserts. The portal posts are connected to each other by means of cross-bars running under the wheel housings to reliably prevent any changes in gauge dimensions due to portal deformation.

An offset secondary suspension system consisting of helical springs and hydraulic cylinders connected in series supports the vehicle module bodies in the portals. The driver can raise the hydraulic cylinders to a preset height above top of rail to achieve the required ground clearance. Despite varying passenger loads, the height above top of rail is maintained at a constant level by an additional control unit. It also enables the trams to continue running on the tracks even in the event of heavy snowfall in winter.

Traction system and electrical equipment

Traction system

Traction and braking are effected by springmounted drive and brake units, which are integrated and suspended laterally in the portal. Both units combine the air-cooled 52 kW asynchronous traction motor and flange-mounted gear unit with brake disc and brake caliper. In the short tram with three intermediate vehicle modules, the two center portals and the end portal are driven; in the long tram with five intermediate, the four center portals are driven. A special control system ensures that the portal makes a sinusoidal movement similar to that of a conventional wheeland-axle set.

Electrical equipment

The vehicle is designed for maximum redundancy. The drive units are fed by two air-cooled traction inverters based on IGBT technology. The braking resistors are self-ventilated. The two auxiliary converter units and the two 24 V battery packs are installed in a roof-mounted container.

The tram is controlled by a Sibas® 32 control unit which is linked to the electrical components via the redundant MVB bus system and Sibas-KLIP stations. Vital functions are also hardwired as a fallback Level.

Passenger compartment furnishings

One air conditioner is mounted on the roof of each vehicle module for the passenger compartment. The compartment is heated with hot air supplied via air outlets in the floor and is ventilated and cooled with air via outlets in the ceiling. Thus, a pleasant environment is maintained inside the compartment regardless of the climatic conditions outside.

The passenger compartments are equipped with loudspeakers and interior displays at the ends of each module to provide passengers with information. Handholds and handrails are color-coded to help visually impaired passengers. Separate areas are provided next to the doors in the passenger modules for stowing baby carriages, bicycles etc.