Proceedings of the Institution of Mechanical Engineers,Part F: Journal of Rail and Rapid Transit

The sleeper to ballast interface plays a crucial role in the stability of ballasted railway track, transferring both vertical and lateral loads safely from the superstructure to the sub-base. However, current conceptual models for the behaviour of the interface are incomplete and too simplistic to assess the response of the track system to the loads exerted by modern trains. For example, the increased curving speeds associated with tilting trains introduce potentially significant combinations of vertical, lateral, and moment loading which are not explicitly considered in current assessment procedures. Also, the relative contributions of the base, crib, and shoulder ballast to lateral sliding resistance are at present poorly quantified. The behaviour of the sleeper to ballast interface was investigated in a series of tests in an apparatus capable of applying combinations of load representative of real trains. This article presents test data quantifying the relative contributions to total sliding resistance of the base, crib, and shoulder. New calculations are presented, which enable the resistance from the crib and various sizes of shoulder ballast to be quantified. The results of the experiments and calculations are compared with each other and with the literature, and reasonably consistent patterns of behaviour are identified.

Transition zones between railway tracks on embankments or natural ground, and fixed substructures such as bridges and culverts, typically require extensive maintenance to retain acceptable track geometry. These high maintenance costs and the potential to cause delays to train services are of major concern for railway infrastructure managers. In view of the importance of the problem, surprisingly little research has been carried out to identify the fundamental causes of the poor performance of transition zones. To better understand the physical mechanisms involved, an extensive monitoring and investigation programme was undertaken on a typical transition zone in the Netherlands, comprising reinforced concrete approach slabs linking the normal track onto a concrete culvert. Accelerations and velocities of the track, soil, and approach slabs in response to passenger trains were measured, from which displacements were calculated. In addition, track settlements and pore water pressures were monitored over a 1-year period. This article presents and discusses the measurements made. The results highlight the problems associated with track quality at a transition zone, including the large dynamic displacements induced during train passage and the tendency for ongoing long-term movement. The implications of these for design and maintenance are discussed.

Trains running on railway tracks on the surface of the ground or in tunnels induce vibrations in the ground which propagate away from the track. These may be experienced as feelable vibration or as audible rumbling noise in the buildings nearby, both of which are difficult to control. As the properties of the ground differ widely between locations they must be characterized for a particular site in order to make reliable predictions. This article describes field measurements of the vibration at two sites with soft clay soil in Southern England. The properties of the ground material, including its layered structure, have been identified from comparisons between results of a layered ground model and measurements obtained using impact excitation. Presentation in the wavenumber-frequency domain is particularly helpful for this purpose. Measurements of vibrations from passing trains are then compared with predictions using a semianalytical model for ground vibration from trains and good agreement is found.

In this paper a new method is used to calculate unsteady wind loadings acting on a railway vehicle. The method takes input data from wind tunnel testing or from computational fluid dynamics simulations (one example of each is presented in this article), for aerodynamic force and moment coefficients and combines these with fluctuating wind velocity time histories and train speed to produce wind force time histories on the train. This method is fast and efficient and this has allowed the wind forces to be applied to a vehicle dynamics simulation for a long length of track.

Two typical vehicles (one passenger, one freight) have been modelled using the vehicle dynamics simulation package ‘VAMPIRE^®’, which allows detailed modelling of the vehicle suspension and wheel—rail contact. The aerodynamic coefficients of the passenger train have been obtained from wind tunnel tests while those of the freight train have been obtained through fluid dynamic computations using large-eddy simulation. Wind loadings were calculated for the same vehicles for a range of average wind speeds and applied to the vehicle models using a user routine within the VAMPIRE package. Track irregularities measured by a track recording coach for a 40 km section of the main line route from London to King's Lynn were used as input to the vehicle simulations.

The simulated vehicle behaviour was assessed against two key indicators for derailment; the Y/Q ratio, which is an indicator of wheel climb derailment, and the Δ Q/Q value, which indicates wheel unloading and therefore potential roll over. The results show that vehicle derailment by either indicator is not predicted for either vehicle for any mean wind speed up to 20 m/s (with consequent gusts up to around 30 m/s). At a higher mean wind speed of 25 m/s derailment is predicted for the passenger vehicle and the unladen freight vehicle (but not for the laden freight vehicle).

The article presents an extensive survey of experimental data on rolling contact fatigue (RCF) crack shape and propagation characteristics in rails removed from service, where such cracks are angled to the rail axis. The data include re-analysis of previously published experimental data to extract crack shape information and new experimental work on crack shapes at different stages in the early RCF life. Periods from initiation (ratcheted ‘flake cracks’) have been considered through very early growth to the limit of one prior austenite (PA) grain and on to rail-head visual cracks. Techniques included multi-sectioning through single cracks and crack zones, on used rail and test discs, to build up real three-dimensional (3D) data on crack shapes and propagation characteristics. This data have been compared with the UK rail system guidance charts relating to visual crack length and respective vertical depth; all data fell within the indicated guidance zones. The configuration of such angled cracks, typically found in curves, so aligned due to the vector of both lateral and longitudinal traction, rather than just axially, was identified as an important case for modelling. A fracture mechanics-based model has been developed to predict modes I and II stress intensity factors for such cracks covering multiple PA grains. An important geometry effect is revealed by which a contact approaching a crack angled to the rail axis is effectively ‘offset’ from the approach direction considered in 2D models, thereby resulting in lower predicted peak stress intensity factor values, compared with 2D, for the prediction of crack growth rates.

Rail signalling in the UK has seen a move from mechanical lever frame boxes to entry and exit signalling, and on through to situating signallers within a visual display unit-based workstation environment. These developments have taken place in tandem with changes such as making the signallers more remote from their area of control and the introduction of automation. These changes have implications not only at a cognitive level for factors such as workload and situation awareness, but also at an organizational level, such as the shift away from traditional career progression, and the resulting implications for training and the development of expertise. Understanding the implications of the signalling interface and the design implementation of automation is critical in facilitating more effective performance, safety, and signaller well-being, as well as informing the design of future rail control systems. Bainbridge articulated a set of ironies of automation — unintended consequences of introducing automation that may not be beneficial to the overall system effectiveness. The work presented in this article uses a structured observation approach to examine behavioural indicators of the impact of automation, either as a successful tool to support signalling or as a source of some or all of the ironies noted by Bainbridge. The work was conducted over a period of 2 years, to investigate the effect of levels of automation on rail signallers’ activity and workload as part of the EPSRC Rail Research UK B6 programme.

This article is concerned with the role of innovation in cost reduction and the mechanisms for bringing it about. In the first section, it investigates the efficiency of UK's railways through the medium of cost benchmarking of both UK and continental European costs. It finds that Britain's rail infrastructure manager faces an efficiency gap of 40 per cent against European best practice and that train operating costs have also risen substantially, both because of rising factor prices (wages and fuel) and because of deteriorating productivity. It then explores the situation surrounding incentives for shaping technological innovation through a series of semistructured interviews with senior managers representing a wide range of railway interests. This section highlights the presence and successful functioning of the commercial mechanism for technology development in the industry both through natural commercial factors and through mechanisms such as track access charges. Finally, it studies the feasibility of modelling systems subject to technological change, with the aim of creating a methodology to assess, at an early stage in the development cycle, the physical impact innovation might have on the existing system. It finds that the objective data needed to construct such models can be extracted from existing technical standards and that systems engineering techniques provide a suitable framework for structuring and linking that data.

Recent increases in railway patronage worldwide have created pressure on rolling stock and railway infrastructure through the demand to improve the capacity and punctuality of the whole system, and this demand must also be balanced with reducing life-cycle costs. Condition monitoring is seen as a significant contributor in achieving this. The emphasis of this article is on the use of sensors mounted on rolling stock to monitor the condition of infrastructure and the rolling stock itself. This is set in the context of modern rolling stock being fitted with high-capacity communication buses and multiple sensors, resulting in the potential for advanced processing of collected data. This article brings together linked research that uses a similar set of rolling stock sensors, and discusses: general usage and benefits, a track defect detection method, running gear condition monitoring, and absolute train speed detection.

Electric railways collect power from the infrastructure via various current collection systems. For high-voltage AC- and DC-powered railways, this is usually achieved using overhead electrification equipment and a train-borne pantograph. The dynamics of such systems are well understood, and the systems are able to be operated under a range of conditions and speeds. Lower-voltage DC-powered railways (<1500 V) use a current collecting shoe as part of a shoegear system and track side electrification infrastructure in the form of a conductor rail. The dynamics of such systems are equally as complex as those of overhead systems. This is due to the interaction between the conductor rail and the track system, coupled with the dynamics of the conductor shoe assembly, which are mechanically linked with the bogie and axle systems. The systems also collect high currents (<2000 A), and therefore maintaining an effective electrical contact is essential. The interface between the conductor shoe and conductor rail is regulated through standards and guidelines. However, there are numerous engineering challenges in the effective management of the whole system that have yet to be addressed. The mechanical design of the system must balance the requirements of good fatigue life with appropriate impact strength. Other issues such as removal of contaminants from the conductor rail surface and shoe wear also have an impact on the design.

This article presents some experimental results from a bogie-mounted instrumentation system designed to monitor a typical example of a shoegear assembly operated on the UK railway system. The results indicate that the shoegear broadly performs in accordance with the design guidelines. Several points of loss of contact were observed, and it is shown that the contact force between the conductor shoe and rail can be estimated. The mean force was found to vary with third rail height, but a wide distribution of forces is found at any one height because of hysteresis in the shoegear. Large, but short-term, forces and torques occur because of third rail irregularities and ramps.

When standing and exposed to vibration in trains, passengers and crew may seek support by leaning on a surface or holding a bar or a handle that alters the transmission of vibration to their bodies. The effects of such contact on the discomfort caused by vibration have not been previously investigated. This study was designed to investigate the effects of postural supports on the discomfort caused by fore-and-aft and lateral whole-body vibration in the frequency range 0.5—16 Hz. Using the method of magnitude estimation, 12 standing male subjects judged the discomfort caused by five magnitudes of sinusoidal vibration at six frequencies (0.5, 1.0, 2.0, 4.0, 8.0, and 16 Hz) and in two directions (fore-and-aft or lateral) while using four different postural supports: no support, holding a vertical bar, leaning with back support, and leaning with shoulder support. Equivalent comfort contours were constructed, showing how discomfort depends on the vibration frequency over a range of vibration magnitudes with each support. Compared to standing with no support, holding a vertical bar had only a minor effect on the discomfort caused by either fore-and-aft or lateral vibration. At frequencies greater than about 2 Hz, leaning backwards against a back support increased the discomfort caused by fore-and-aft vibration and leaning sideways against a shoulder support increased discomfort caused by lateral vibration. Frequency weightings derived from the equivalent comfort contours show that the weightings suggested in current standards do not provide good predictions of the frequency dependence of discomfort caused by vibration when standing without any support or when supported and holding only a bar. It is concluded that leaning, with the back or shoulder supported, increases the discomfort caused by vibration in a direction normal to the body surface at frequencies greater than about 2 Hz. Currently, standardized frequency weightings do not provide good predictions of the discomfort caused by horizontal vibration when standing without holding a support.

Vehicle braking in non-electrified rail systems wastes energy. This article considers two approaches to reducing braking losses in regional diesel trains: efficient driving strategies and regenerative braking. The interaction of these two approaches is critical in specifying the requirements of a hybrid train and assessing the relative fuel saving. Computational models of conventional and hybrid diesel-hydrodynamic regional trains have been developed using real route data to generate a simple control algorithm and investigate the effect of driving strategy on fuel consumption and journey time. The current modelling predicts fuel savings of up to 40 per cent for the hybrid train when an aggressive control strategy is used. This fuel saving is halved when an efficient driving strategy is employed, which also reduces the required energy storage capacity. The model provides a tool for identifying effective control strategies which should be implemented to reduce fuel consumption for both conventional and hybrid trains.