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The railway track system is the platform by which loads from moving trains are transferred to the underlying soil or supporting infrastructure such as bridges. The most common type of railway track system is ballasted track, which has been in use for over a century. Ballasted track has proved versatile. It can be constructed using locally available materials and with modifications to the rails and sleepers, crossings transferring trains from one route to another can be created. The structure of a ballasted track system consists of two main parts. The upper portion, termed the superstructure, comprises the rails, fastenings and sleepers. It is formed of components whose shape, stiffness and strength are designed and closely controlled. Below the superstructure is the substructure, which comprises the ballast and sub-ballast. Although the materials used in the substructure may have been specified, their engineering properties and geometric placement are less well controlled. In this chapter, we will explore how a typical ballasted track system transfers load to the ground and the ways in which the track form deteriorates, requiring maintenance and eventually renewal.

This chapter introduces a model of efficiency-wage competition along the lines put forward by Hahn (1987). Specifically, I analyze a two-firm economy in which employers screen their workforce by means of increasing wage offers competing one another for high-quality employees. The main results are the following. First, using a specification of effort such that the problem of firms is well-behaved, optimal wage offers are strategic complements. Second, the symmetric Nash equilibrium can be locally stable under the assumption that firms adjust their wage offers in the direction of increasing profits by conjecturing that any wage offer above (below) equilibrium will lead competitors to underbid (overbid) such an offer. Finally, the exploration of possible labor market equilibria reveals that effort is counter-cyclical.