Stray current is a relevant phenomenon in particular for DC electrified transportation systems, affecting track and infrastructure within the right of way and other structures and installations nearby. It worsens with time and the level of protection depends on timely maintenance, as well as correct design choices. The assessment of track insulation is the starting point for both stray current monitoring systems and at commissioning or upon major changes. Standardized methods (ref. EN 50122-2 or IEC 62128-2) have been almost unchanged in the last 20 years but suffer from accuracy issues and variability due to parameters and conditions not under the operator’s control. The uncertainty of test methods is increasingly important now that contractual specifications require a high level of insulation for new systems. A critical discussion and analysis of the sources of variability and practical constraints is proposed, followed by an evaluation of uncertainty, with the objective not only to assess the accuracy of the provided results, but also to foster research on innovative, more flexible and accurate methods.

Energy efficiency is more and more important for modern electrified transportation systems, requiring an understanding of the various indexes of performance (regenerability, receptivity, and energy losses, thus including braking recovered energy and energy loss in catenary) and of the influence of the main system parameters (headway, line voltage, substation separation, etc.). By means of electromechanical simulation, the most relevant parameters and system conditions are identified as influencing the efficiency performance and optimization capability. Besides the assessment of such efficiency performance indexes, identifying their typical ranges of variation, one further outcome is the identification of characteristic system parameter combinations that lead to extreme variations in the system energy efficiency itself. Such peculiar variations are caused by occasionally synchronized patterns of trains along the line and result in a significant local increase or decrease in efficiency. Efficiency drop scenarios in particular should be taken into consideration for worst-case analysis and to devise effective mitigations. To this aim, the effect of differently distributed passenger stations is considered.

The testing of rolling stock for the assessment of disturbance in signalling circuits is considered with a focus on the measurement process and the selection of operating conditions. The definition of interference limits is briefly reviewed, but they are considered an external input. The spectral behavior of acquired signals and the evaluation of repeatability are instead discussed with the help of three different real test cases, considering correspondence between similar operating points and differences as rolling stock operation evolves during a test run. Repeatability evaluated as standard deviation is in the order of 3% to 5% in the harmonic and audio frequency range for the different systems, slightly lower for AC railways; above about 10–15 kHz it increases to 30%. Uncorrelated components (with much lower amplitudes) may show much higher dispersion.

Stray current is a relevant phenomenon in particular for DC electrified transportation systems, affecting the track and infrastructure within the right of way and other structures and installations nearby. It worsens with time and the level of protection depend on timely maintenance, besides correct design choices. The assessment of track insulation is the starting point for both stray current monitoring systems and at commissioning or upon major changes. Standardized methods (ref. EN 50122-2, or IEC 62128-2) are almost unchanged in the last 20 years, but suffer from accuracy issues and variability due to parameters and conditions not under operator’s control. A critical discussion and analysis of the sources of variability and practical constraints is proposed, followed by the evaluation of uncertainty, with the objective not only to assess the accuracy of provided results, but to foster research on innovative, more flexible and accurate, methods.

Testing of rolling stock for assessment of disturbance to signalling circuits is considered with focus on the measurement process and the selection of operating conditions. The definition of interference limits is briefly reviewed, but they are considered an external input. The spectral behaviour of acquired signals and the evaluation of repeatability are instead discussed with the help of three different real test cases, considering correspondence between similar operating points and differences as rolling stock operation evolves during a test run. Repeatability evaluated as standard deviation is in the order of 3% to 5% in the harmonic and audio frequency range for the different systems, slightly lower for AC railways; above about 10-15 kHz it increases to 30%. Uncorrelated components (with much lower amplitude) may show much higher dispersion.