Turnkey provision of Selective Door Operation for Mark 4 coaching stock for Transport for Wales Rail

Article: Turnkey provision of Selective Door Operation for Mark 4 coaching stock for Transport for Wales Rail


In 2021, DB ESG conducted a feasibility study into the requirements for and the installation of a Selective Door Operation (SDO) system for Transport for Wales Rail (TfWR) for use on their fleet of Mark 4 (MK4) coaching stock. The study considered both manual and automatic SDO systems.

TfWR operates a fleet of locomotive hauled MK4 coaching stock on intercity services. This fleet was not fitted with SDO, but there was a need for such a system to be in operation at stations with shorter platform lengths, where the platforms were too short to accommodate the complete trainset.

Following on from this feasibility study, in December 2021, DB ESG received a contract from TfWR to design and install a manual SDO system onto TfWR’s fleet of eight train rakes consisting of Mk 4 coaches and driving van trailers (DVT). DB ESG was, at this time, already working on this fleet of Mk 4 rakes, following contracts received from TfWR and Eversholt Rail, to complete the modifications necessary to enable Mk 4 coaching stock to be operated in push-pull format with Class 67 locomotives and DVTs.

TfWR decided on a manual system, following a detailed review of the associated risk and business case, as this could be delivered within the required timescale for fleet introduction. This manual SDO system was to be designed, such that it could function as the manual override for an automatic SDO system if this was retrofitted to this fleet at some point in the future.


DB ESG was responsible for the engineering, design, approvals, material procurement and installation for this SDO project.

The manual SDO system was implemented as a new relay logic system, overlaid onto the existing hard-wired door controls, and operated by a new Guard’s Key Switch (GKS) that had additional positions and contacts.  This new GKS would allow the Guard to select which doors to enable at stations.

As a safety critical system, the specification, design, and installation of the SDO system was underpinned by a structured safety management process, in line with the CSM-RA process.

Work Undertaken by DB ESG

  • Capture and agreement of project requirements into a system functional requirements specification.
  • Conduction of vehicle surveys to validate the installation locations of all new components and wiring harnesses and confirm existing system functionality.
  • Development of a concept design for the SDO system and its installations.
  • Creation of 3D CAD models to validate the installation.
  • Production of a 2D design pack, including the update of existing electrical schematic drawings.
  • The concept design was turned into a detailed design, with updated drawings and as-build drawings produced following first-in-class fitment.
  • The design utilised design-for-manufacturing techniques, such as extensive use of pre-built and tested assemblies, to minimise the time and risk associated with vehicle modification.
  • Application of human factors best practice and analysis throughout the project, including leading workshops with train crew to optimise the operability of the system.
  • Engineering analysis of the SDO modification was undertaken to ensure that the design solution met the functional and safety requirements and complied with all applicable standards, including carrying out: -
    1. structural engineering calculations for all new mechanical assemblies and fixings, including Finite Element Analysis (FEA) of the more complex installations.
    2. bogie movements assessment of the new cable harness route over the bogie.
    3. fire performance assessment, including completion of a fire safety and materials inventory list.
    4. functional safety justification including detailed failure modes and fault tree analysis.
    5. electromagnetic compatibility assessment.
    6. electrical safety assessments.
  • The existing MK4 maintenance instructions were reviewed and updated.
  • Railway Approvals Ltd. independently approved and certified the SDO modification.
  • Creation and implementation of a robust safety management process for the project.
  • Provision of all the materials required for the SDO system in rake kit formation. The kits containing all the materials necessary to complete the installation.
  • 12 months warranty was provided on all supplied materials and equipment.
  • The first-in-class fitment was overseen, and support was provided, as required, for the remaining rakes.
  • Production of a testing and commissioning strategy, designed to provide a staged approach to implementation of the new system, including type and routine tests: -
    1. tests on pre-manufactured cable harnesses and panel assemblies.
    2. electrical installation tests on each completed vehicle.
    3. functional tests on each completed rake to verify SDO performance.
    4. testing of existing train systems to ensure that they haven’t been impacted by the modification.
    5. type testing of the first rake to be modified to validate the SDO functionality and support the safety management process.