Supporting Network Rail
to Deliver the Knaresborough K9
Signal Life Extension Project
Client: Network Rail
Location: Knaresborough Station, HAY1 Line (16M 50ch)
Sector: Rail Infrastructure – Signalling
Services Provided: Signalling Design (ES4/ES5), Technical Assurance, Integration of legacy Systems
Project Duration: December 2024 – March 2025
Overview
Mosaic Rail were engaged by Network Rail to provide signalling design and assurance services for the Knaresborough K9 Signal Life Extension Project, part of a safety-critical programme addressing structural failure risks and modernising signalling control at a Grade II listed station.
The existing K9 semaphore signal was mounted on a cantilever gantry on the Up platform, signalling trains from the Down platform. Following reports of structural instability, emergency civil works were undertaken to prevent collapse. Mosaic Rail were tasked with developing a safe and compliant signalling solution that removed the defective structure, restored passenger access to the platform, and achieved full system integration with the heritage mechanical interlocking still operational at Knaresborough Signal Box.
The Challenge
The K9 cantilever signal structure was declared unsafe after three of its four legs were found overloaded and progressively failing. Immediate stabilisation measures restricted station access and required a permanent solution that balanced heritage constraints, operational continuity, and modern safety compliance.
Challenges included:
- Designing a replacement colour light signal within a heritage-controlled environment requiring Listed Building and Historic England approval.
- Integrating a modern 3-aspect Dorman iLS LED signal into the existing mechanical lever frame and BR930 relay-based control system.
- Managing limited space within the relay location and reusing legacy circuits to minimise new infrastructure.
- Ensuring seamless interface control between electro-mechanical and modern electronic components.
- Delivering design, assurance, and testing within a compressed six-month timeframe, while maintaining operational safety and compliance with Network Rail standards.
- Provision of a new Mosaic tile Illuminated diagram at Knaresborough Signal Box.
Our Approach
Mosaic Rail undertook the full ES4 and ES5 signalling design phases developing an innovative design strategy that combined new LED technology with existing mechanical control principles.
Our approach focused on compatibility, minimal disruption, and long-term maintainability, including:
- Development of a hybrid electro-mechanical control circuit, retaining lever operation while introducing electrical aspect control and AWS.
- Early interface definition workshops with Network Rail’s project engineers and LB Foster to manage both control and indication system upgrades.
- Design of new relay-based control logic using BR930 and BR960 twin relays to create capacity within the existing relay room.
- Integration of a new mosaic-style illuminated diagram and upgraded indication units within the signal box blockshelf.
- Careful heritage coordination to ensure that new assets blended with the listed station environment.
- Collaborative management of parallel ES4/ES5 design phases to meet the accelerated delivery window.
The Solution
Mosaic Rail’s design facilitated the safe replacement of the obsolete K9 semaphore signal with a 3-aspect Dorman iLS LED colour light, achieving full functionality within the legacy Knaresborough control system.
Key solution features included:
- Conversion of mechanical control (Lever 9) to electro-mechanical operation via rotary circuit controllers and relay logic.
- Addition of new AWS equipment at a standard distance of 180m to mitigate SPAD risk.
- Retention and enhancement of existing track circuit and interlocking controls, with updated approach release and aspect sequencing logic.
- Renewal of Knaresborough Signal Box indication systems, including new aspect indicators and LB Foster’s mosaic-style illuminated diagram.
- Modification of power and circuit architectures within the relay room to support new LED signal loads and maintain redundancy.
- Full compliance with NR/L2/SIG/30035 and Common Safety Method (CSM) standards.
Results & Impact
The scheme successfully achieved the safe removal of a structurally unsound signal, reinstating full passenger access while modernising operational control through seamless integration of new and legacy systems.
Key Takeaways
Legacy integration expertise: Mosaic Rail demonstrated advanced understanding of electro-mechanical signalling, enabling safe coexistence of old and new technologies.
Collaborative assurance: Close coordination between signalling, civils, and heritage disciplines ensured compliance with safety and conservation requirements.
Innovation under constraint: The project delivered a fully compliant safety upgrade within significant physical and regulatory restrictions.
Design efficiency: Adoption of digital design tools, correlation waivers, and a structured review process enabled efficient design and approval cycles.
Partner with Mosaic Rail for signalling design and assurance services that modernise infrastructure, enhance safety, and improve operational resilience across the UK rail network.
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Key Outcomes:
- Safe replacement of the K9 semaphore signal with a compliant LED colour light system.
- Full interoperability between mechanical lever frame control and relay-based modern signalling.
- Enhanced operational safety through AWS installation and improved SPAD mitigation.
- Digital renewal of the signal box indication panel for improved clarity and reliability.
- Accelerated delivery under a parallel ES4/ES5 programme, meeting the six-month completion target.
