What can one failed fastening component teach us about the future of railway safety?

On 12 July 2013, Intercites train No 3657 was operating a scheduled long-distance passenger service on the ParisOrleansLimogesToulouse (POLT) main line, a principal rail corridor connecting Paris with central and southern France.

As the train approached the northern entrance to Bretigny-sur-Orge station, the character of the railway began to change. The continuity of plain line gave way to a more complex environment: a point and crossing layout, where rails intersect, diverge, and rely on precise geometry maintained through a combination of rail form and bolted connections.

It is here that the track becomes less forgiving, where small imperfections are absorbed less easily, and where wheelrail interaction becomes more concentrated and severe. Within this transition zone, something went critically wrong.

The subsequent sequence of events was later formally established during the investigation into the Bretigny-sur-Orge derailment.

What went wrong?

From an engineering perspective, a switch and crossing are not simply a section of track. It is one of the most mechanically demanding environments in railway infrastructure.

Unlike plain line, where rails provide continuous support and guidance, a crossing introduces deliberate discontinuities. Wheels must traverse gaps, negotiate geometry changes, and remain controlled through a system that depends on precise alignment of multiple interacting components.

To make this possible, the system relies heavily on bolted joints. Fishplates, or tight plated joints, clamp adjacent rail sections together, maintaining alignment and enabling load transfer across rail ends. When correctly installed and maintained, they provide a stable and robust connection under repeated dynamic loading.

However, this stability depends on a single critical condition: the joint must remain fully secured, maintaining clamping force over time. In railway tracks, the steel rails expand when hot and contract when cold. That movement is unavoidable because steel changes length with temperature.

At Bretigny-sur-Orge, that security had been lost. Cracking had developed, gradually altering how loads were distributed through the jointed assembly. As the rail deteriorated, increasing stress was transferred into the bolted connection.

Under repeated loading from passing trains, this change in load path began to affect the fasteners. One bolt fractured, reducing clamping force across the joint. With restraint weakened, the remaining bolts were subjected to higher loads and less stable conditions.

Over time the fishplate rotated into the wheel passageway during the train's passage. The structural joint component had become a direct physical obstruction within the wheel path and launched the train off the track. The first two derailed cars remained on track 1 and eventually lay on their right side. The third derailed car went across between tracks 1 and 3 and swept platform 3 for about 100 metres. The last car stopped on platform 3, without lying down. Tragically, seven people lost their lives and 428 were injured in the incident.

Why do rail fasteners loosen under vibration?

The critical lesson is not just about the joint itself, but about vibration-driven loosening. Rail environments expose fasteners to: continuous cyclic loading; impact forces at crossings; and thermal movement of rail; long-term vibration fatigue. Once preload is lost, joints begin to work loose progressively. In this condition, conventional nuts can unwind over time unless positively locked.

Hardlock Nuts are a type of vibration resistant fastener designed specifically to resist self-loosening under vibration. Unlike standard fasteners that rely only on friction, Hardlock uses a mechanical wedge-locking principle. This means: they do not loosen under vibration; they maintain preload over long service life; they remain stable in thermally active joints; and they reduce reliance on re-torquing and reactive maintenance. In short, if Hardlock fasteners are correctly installed, the kind of progressive loosening seen in degraded tight plated joints is far less likely to occur.

Standards and industry response

For infrastructure managers operating similar assets, including Network Rail, the event highlighted a shared vulnerability: in switch and crossing systems, small losses in fastener integrity can escalate into system-level failure when occurring in the wrong geometric and loading context.

Following the 2013 Bretigny-sur-Orge derailment, the Rail Safety and Standards Board (RSSB) queried Network Rail about the potential risk of loose fishplate fasteners within the UK rail network. In response, Network Rail launched a programme to evaluate anti-loosening systems for tight plated joints. This work ultimately led to the approval and rollout of Hardlock Nuts for certain fishplate applications, formalised under Network Rail's Certificate of Acceptance PA05/02077 for use in approved rail joint configurations.

13 years on

We are now more than a decade on from Bretigny, yet many legacy tight plated joints remain in service without upgraded locking systems. That means the same underlying risk factors still exist: vibration, thermal movement, preload loss over time and progressive loosening in high-stress areas.

The Bretigny-sur-Orge derailment demonstrates how bolted joint reliability and rail safety depends on the long-term integrity of seemingly simple but safety-critical components.

The key distinction is simple. Loose or degrading joints create movement, fatigue and escalating risk, while properly locked tight-plated joints maintain stability under vibration and temperature cycling.

Staytite can help. Hardlock Nuts provide a way to make that second condition far more reliable in practice. As a supplier of Hardlock Nuts, Staytite helps ensure correct assembly practices, including proper bolt tensioning and alignment. We provide engineering support for rail infrastructure projects, including free on-site installation support for Metric Fishplate Kits.

The Staytite Rail team also supplies a wide range of fasteners and engineered components for rail applications, supporting both standard and nonstandard requirements. In addition, we can assist with heritage specific rail systems where legacy track geometry or nonstandard specifications require tailored fastening solutions.