Andreas Haigermoser

Assessment of safety against derailment using simulations and vehicle acceptance tests: a worldwide comparison of state-of-the-art assessment methods

The assessment of derailment safety of new railway vehicle designs is a fundamental concern worldwide. Although the methods used for assessment in different countries and regions vary considerably, the fundamental mechanisms being addressed are the same. This paper provides a detailed review of the current state-of-the-art methods for derailment safety assessment in several regions and countries including Europe, UK, USA, and Russia. Brief overviews of the methods used in China, Korea, and Japan are also included. Similarities and differences are discussed, including testing and computer simulations. References are provided for the origins of the methods and safety performance criteria used in each region. Recommendations are made for improving the assessment methods, especially the use and validation of computer simulations.

Road and track irregularities: measurement, assessment and simulation

Road and track irregularities have an important influence on the dynamic behaviour of vehicles. Knowledge of their characteristics and magnitude is essential for the design of the vehicle but also for comparable homologation and acceptance tests as well as for the planning and management of track maintenance. Irregularities of tracks and roads are regularly measured using various measurement technologies. All have advantages and weaknesses and require several processing steps. Characterisation of irregularities is done in the distance as well as in the wavelength domain. For rail irregularities, various distance domain description methods have been proposed and are in use. Methods have been analysed and compared with regard to their processing steps. Several methods have been analysed using measured irregularity and vehicle response data. Characterisation in the wavelength domain is done in a similar way for track and road irregularities. Here, an important issue is the estimation of the power spectral densities and the approximation by analytical formulas. For rail irregularities, periodic defects also play an important role. The use of irregularities in simulations requires various processing steps if measured irregularities are used, as well as if synthetic data are utilised. This paper gives a quite complete overview of rail irregularities and points out similarities and differences to the road.

Track geometry evaluation method based on vehicle response prediction

Testing of the running characteristics of railway vehicles requires well-defined boundary conditions like track geometry quality. Test sections with the same track geometry quality must lead to the same dynamic vehicle response (VR) forces. The state-of-the-art methods do not fulfil this important requirement for a track quality definition. Our proposed method for track geometry assessment considers the vehicle/track interaction. ‘Representative’ transfer functions are used for the prediction of the vehicle reaction. Therefore, the results show a significant enhancement of the correlation between the track assessment quantities and the VR forces.

Describing and assessing track geometry quality

Track geometry quality has an important influence on the dynamic behaviour of the vehicles. Control of track geometry during the maintenance process and for the vehicle assessment (homologation) is necessary. Within the project, DYNOTRAIN methods for describing and assessing track geometry have been studied. Data from a comprehensive test campaign have been used to measure the effectiveness of different track geometry assessment methods. The vehicle behaviour has been studied by a multiple regression model with varying track geometry description methods. It had been shown that it is essential to include track geometry in the vehicle assessment process in a proper way. Depending on the assessment quantity and the vehicle type, the mostly used method in Europe (standard deviation in wavelength range 3–25 m) allows in combination with speed, cant deficiency and curvature the explanation of 20–80% of the total variation of the vehicle reaction. Other methods and ‘new’ alternative methods intended to model a typical vehicle behaviour mostly give no or only a small improvement.

Track loading limits and cross-acceptance of vehicle approvals

The requirements for track loading limits are one of the main barriers to simple cross-acceptance of vehicles where rolling stock that is already operating successfully in one (or more) networks has to be retested before it can be approved for operation on another network. DynoTRAIN Work Package 4 studied this area in order to determine whether the additional requirements were justified, or if the process could be made much cheaper and simpler without increasing the risk of track deterioration for the networks. The review of national requirements identified modified criteria and limit values for track forces in some member states; however, these can be obtained from additional analysis of the normal test results with no new tests required. The influence of design rail inclination has also been found not to be significant, provided a realistic range of wheel–rail contact conditions are included in the tests. For line speeds greater than or equal to 160 km/h, the current standards for track construction across the member states appear to be similar. On lower speed lines in some countries, a ‘weaker’ track condition may require a lower limit on one of the vehicle assessment parameters. Track dynamics modelling has shown that the vehicle assessment parameters used in international standards are suitable for use in cross-acceptance for track forces. The use of multiple regression analysis allows the estimated maximum value for relevant parameters to be evaluated for different target conditions and then compared with the appropriate limit value, or with values for existing, comparable vehicles. Guidance has also been provided on the relevant parameters to consider when developing operating controls for different types of track deterioration.