Undergrounds and other metropolitan railway systems are characterized by their intense traffic, lasting up to 20 h per day, and so they need their maintenance work programmes to be optimized, implying an optimization of the monitoring processes. This article proposes an alternative to the traditional optical methods for monitoring rail profiles which can only be carried out by special vehicles. This is a new procedure that obtains the rail profile by means of inertial methods. The model this work is based on takes its input from the vertical accelerations produced in railway axles measured in trains running on regular services and calculates the rail irregularities that have originated them. The model uses the Fourier transform in order to solve the equations and find the transfer function that relates the input function and the output function in the frequency domain. The solution is then reverted into the time domain by applying the inverse Fourier transform. Data input comes from real measurements taken on line 9 of the Madrid underground, and the model's effectiveness was then analysed by comparing the output data with the rail profile taken using optical methods.

A railway track stretch comprising three different track typologies (i.e., ballasted track, asphalt slab track and concrete slab track) has been modeled using a three-dimensional Finite Elements model, which has been calibrated and validated using real acceleration records. In this model, two different analyses have been run: a static analysis to assess the stiffness evolution and a dynamic analysis to calculate the accelerations induced by the train loads along the transition zones. These analyses have been used to assess the performance of three different techniques existing in the literature to improve the structural behavior of the track in the transition areas: the variation of the stiffness of the elastomers, the implementation of additional rails and the use of resilient mats. Results have demonstrated that these techniques perform generally better in the track vertical stiffness transition between the concrete and asphalt slab tracks while the dynamic response is not significantly altered in any scenario.