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Formal verification of railway interlocking and its safety case

Lookup NU author(s): Dr Alexei Iliasov, Professor Alexander RomanovskyORCiD



This is the authors' accepted manuscript of a conference proceedings (inc. abstract) that has been published in its final definitive form by The Safety-Critical Systems Club, UK, 2022.

For re-use rights please refer to the publisher's terms and conditions.


The increasing complexity of modern interlocking poses a major challenge to ensuring railway safety. This calls for application of formal methods for assurance and verification of their safety. We have developed an industry-strength toolset, called SafeCap, for formal verification of interlockings. Our aim was to overcome the main barriers in deploying formal methods in industry. The approach proposed verifies interlocking data developed by signalling engineers in the ways they are designed by industry. It ensures fully-automated verification of safety properties using the state of the art techniques (automated theorem provers and solvers), and provides diagnostics in terms of the notations used by engineers. In the last two years SafeCap has been successfully used to verify 26 real-world mainline interlockings, developed by different suppliers and design offices. SafeCap is currently used in an advisory capacity, supplementing manual checking and testing processes by providing an additional level of verification and enabling earlier identification of errors. We are now developing a safety case to support its use as an alternative to some of these activities.

Publication metadata

Author(s): Iliasov A, Taylor D, Laibinis L, Romanovsky A

Publication type: Conference Proceedings (inc. Abstract)

Publication status: Published

Conference Name: Safety-critical Systems Symposium 2022

Year of Conference: 2022

Online publication date: 08/02/2022

Acceptance date: 07/10/2021

Date deposited: 01/10/2021

Publisher: The Safety-Critical Systems Club, UK