Assessment of Tram Vehicle’s Compatibility with Planned Track Layouts

Customers: Würzburger Straßenbahn GmbH (WSB), Germany; HAVAG Hallesche Verkehrs-AG, Germany; Basler Verkehrs-Betriebe (BVB), Switzerland

Project tasks

• Ensuring Tram Compatibility: Confirmation that existing tram vehicles can operate on planned track layouts
• Track Layout Optimisation: Proposal of alternative track layouts that can be passed safely and without causing damage or derailment to the trams

Our approach

The track layouts of tram systems often have very individual characteristics due to the topography or the historical development of city centers. The tram vehicles need to be compatible for these specific infrastructure conditions. As a result, there is limited standardisation or harmonisation between vehicles and tracks in tram systems. Modern tram vehicles are often multi-articulated vehicles. Their vehicle length can extend over several track elements such as changes in horizontal curvature and changes in vertical gradient. In general, all vehicle sections are connected to each other in an almost torsionally rigid manner – apart from a small amount of flexibility in a few roof joints. Long articulated vehicles are therefore often sensitive to torsional loads, such as those that arise when combining small curve radii and large changes in vertical slope.

When planning new tram tracks, the question therefore regularly arises whether the existing vehicles can negotiate the newly planned route. The safety objectives are especially the safety against derailment and the damage-free bearing of the loads that occur. Furthermore, sufficient gaps between vehicle parts or the ground clearance underneath the vehicle can also be objectives.

PROSE investigates trafficability while using multi-body system (MBS) simulations, as they are used internationally during the development of rail vehicles. The simulation model contains the specific properties of the vehicles under assessment. This includes the overall vehicle concept, the detailed mass distribution as well as the individual running gears with their suspension levels, etc. Furthermore, the simulation model includes the track, which is characterised by the track layout to be tested, local track gauges and groove widths as well as any flat grooves. In addition, elastic track bed properties or geometrical track irregularities can be considered.

In the computer simulation, the vehicle models are moved over the planned tracks. The relevant combinations of boundary conditions such as the load, winter stiffening of the rubber springs, the wheel/rail profiles, the running speed etc. are considered. The simulation results are evaluated against assessment criteria from standards (e.g. safety against derailment) or evidence documents of the vehicle (e.g. bearable loads). If trafficability is not yet ensured, PROSE varies the track layout in a stepwise approach. For this purpose, previously agreed premises are followed which parameters, such as the superelevation or vertical slope etc., should be changed as a priority or must remain unchanged e.g. for urban planning reasons.

Customer benefit

An immediate benefit is the planning reliability that results from the proven trafficability of the new track. At the same time, the risk of late effects such as cracks occurring in the vehicle structure after the construction work has been completed is minimised.