Without independent evaluation, there is no safe start-up: The key role of the ISA in the rail sector
Published 17.09.26
6 mins read
This milestone is not a mere administrative formality. It is the convergence point where years of design, engineering, and testing demonstrate with technical evidence that the system safeguards the lives of its users. And it is precisely at this point that the Independent Safety Assessment (ISA) becomes the cornerstone that upholds the entire operational safety structure.
Authorizing is not certifying on trust, it's certifying with evidence.
In the modern rail industry, commissioning must never depend on the manufacturer or operator simply declaring that "everything works correctly." It requires the intervention of an expert, impartial third party (with no commercial, financial, political, personal, or any other interest in the project) who systematically audits that risks have been identified, evaluated, and reduced to a tolerable level (EN 50126-1:2018, §6.3).
That role falls to the Independent Safety Assessor (ISA). Their function is to examine, with a precise level of detail, whether the work of designers, integrators, and operators complies with the strictest international standards of functional safety and RAMS (Reliability, Availability, Maintainability, and Safety). In practice, their technical opinion is the condition for the competent authority to grant approval for the start of operations and entry into service of the system.
Currently in Mexico, in the absence of specific local regulation requiring mandatory compliance with safety standards in certain contexts of our region, the rail industry adopts the European regulatory framework as international best practice, aligning with the following reference standards:-
- EN 50126: Railway applications — Specification and demonstration of Reliability, Availability, Maintainability and Safety (RAMS).
- EN 50128: Railway applications — Communication, signalling and processing systems — Software for railway control and protection systems.
- EN 50129: Railway applications — Communication, signalling and processing systems — Safety-related electronic systems for signalling.
Basing assessments on these standards ensures that projects compete under the same parameters of excellence and technical maturity as major rail systems worldwide.
Why is the start of operations the moment of greatest exposure?
The operational start-up concentrates a unique risk: it is the instant when engineering theory meets face to face with the reality of the environment and human behavior. A rail system integrates numerous systems and subsystems, each with distinct engineering specialties requiring high technical capability, including: signalling, rolling stock, command and control systems (CBTC/ETCS), power, civil works and architecture, track superstructure, as well as human-machine interfaces (HMI), among other systems/subsystems — all sharing the same objective: coexisting comprehensively to enable full system functionality and to operate safely and efficiently. The ISA's intervention at this stage allows for:
- Detecting integration gaps that subsystem-level testing tends to overlook, preventing latent failures from materializing once passengers are on board.
- Verifying strict traceability of safety requirements, confirming that every risk identified in early phases was effectively mitigated.- Assessing operational and maintenance maturity, because safety does not end when the work is handed over — it continues in daily operations.
- Providing objective support to the regulatory authority, delivering solid, independent technical judgment rather than commercial promises.
Beyond the ethical commitment to protecting lives, an ISA assessment brings tangible economic value to the project. It drastically reduces costly disruptions, protects operators' reputations, and today is a necessary requirement for accessing high-demand national and international tenders.
Ultimately, approving a rail system cannot rest solely on the judgment of those who built it. It must be grounded in the expert, rigorous, and independent perspective that guarantees the system is truly ready to safely move thousands of people.
Author.
Jovany PereaAccreditation Manager at AuditSafe
