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Noel Samaan, PhD Senior Member IEEE (USA), Member IEE (UK), CPEng

R&D Software Systems Group Ansaldo STS

As the reliance on software is significantly increasing in railway industries replacing electronic, pseudoprogrammable electromechanical devices and wayside signals (in the future), the demand for quantifiable and traceable techniques to determine the trustability and dependability of software is becoming more critical. Given the pressures on delivering projects on-time with inherent heavier contribution of software to decision– making dynamics of train operations whether related to train control, routing, database-driven scheduling or issuance of train orders and, given the rather fluidic nature of software development and change in requirements (when compared with hardware domain), validation of software applications for railway at relatively high confidence levels and low cost is a challenge that has become a significant ingredient to project over-run and higher than estimated project costs.

This paper reviews the requirements for safety-critical systems for railway, highlights the main differences between software and hardware approaches used to determine product reliability and presents a case study to illustrate how modelling and metric-driven approaches to software validation can lead to high assurance levels whilst reducing the validation cost. The paper concludes with a few recommendations where railway industry can benefit from other industries where software became a core activity at later stages of business evolution which demanded the delivery of faster, cheaper and better quality software applications.