Early Stage Specification Process

This section gives detailed guidance on process steps to take a rail project through at the early stage of development. Click on the steps below to jump straight to each step:

The Early Stage Specification Process Steps diagram shows the steps in more detail, it is important to note that these may be iterative, as suggested by the arrows.

A flowchart showing the stages of the early stage specification process; this can also be downloaded as a PDF file from the link below.

This diagram can be downloaded as a PDF file.

Step 1: Requirements and conditional outputs

The first step to developing the specification is to ascertain the Conditional Railway Outputs and their value. This starts with developing requirements which must be evidenced and their value understood to find a Value for Money solution.  Not understanding the value of the requirements, has the potential to waste significant amounts of time chasing solutions.

Understanding the value allows for Concept Solutions to be ‘reverse engineered’ for value and hence guide the development team to viable solutions.

This should relate directly to:

  • What you are trying to achieve & what is the output change to the railway system
  • A translation of the strategic objective and outcomes into railway outputs for passenger and freight users
  • Robust evidence such as demand modelling, market studies, local plans, government policy, revenue forecasts
  • Initial assessment of the value of the benefits to be delivered.
  • Affordability criteria

It is very important to test the concept solutions against the impact of the assumptions and risks. This will:

  • Test the viability of the solution
  • The value for money of the solution and how this could change as assumptions and risks move / materialise
  • Be fundamental to the creation of the cost range 
  • Test the extent of scope and impact 

At this stage it should still be an aim to look at a range of options to deliver the objectives in relation to cost to give clarity on what might be achieved for different levels of expenditure, i.e. is it an option to achieve 80% of desired benefits if costs can be 50% of full scope? Costs are unlikely to be understood at this point, but an understanding should be established of the appetite for trade off in costs and outcomes.

Step 2: Indicative Train Service Specification (ITSS)

Upon completion of concept solutions the next step is to consider a train service specification(s) which meets the requirements and check whether there are any better options available.

The ITSS should be used test assumptions about what level of service and capacity can be delivered and where infrastructure investment may be required to deliver the ITSS.  It is important to remember that the ITSS is not the requirement (a franchise may not choose to run that service), it is a way to articulate a reference case that can drive the decisions on scope.  When considering how to construct the ITSS, there will be trade-offs and links between the proposed level of service (and value of that benefit) and the infrastructure required to deliver that service.  The option selection for infrastructure should refer back to the ITSS to understand what benefit is driving that infrastructure. 

The ITSS is not a timetable,and may not include performance in the initial assessment.  It also may limit its geographic scope and thus may not be a full proxy for how the infrastructure will function in practice.  However, it is a useful tool to test what might be possible and to compare options.  It should not be treated as a requirement unless it is specifically stated that the ITSS is a requirement.

In capacity terms there is always a tension/balance between the frequency of service, the length of a train and the density of seat on a class of train hence the need to check ITSS against demand modelling. 

Network Rail will compile a document in line with TAG in the creation of a business case.  However, funders may wish to explore wider benefits and industry economics further and look, for example, at the value of frequency as well as capacity.

Requirements are still conditional at this early stage and hence so must the ITSS be.  It will require review and iteration as knowledge of its impact is gained.  The skill is to know when to stop iterating and lock down the ITSS for the production of the business case.


  • Combines existing service levels with required service and capacity outputs.
  • contains details of origin, destination, routing, stopping pattern and train characteristics but is not operator specific.
  • Provides the basis for an indicative hourly timetable pattern that can be modelled.
  • Other output such as train class and journey time not included but are needed for modelling.
  • Is also modelled for passenger capacity and compared to demand projections.
  • Is very likely to require iteration as the scale and impact of early versions are better understood.

Step 3: Network analysis and modelling

Having established a set of requirements, concept solutions and an indication of train service it is time to check how these work together. This means using specialist resource to get the ITSS modelled on existing infrastructure to ascertain pinch points that require interventions. Remember the Early Stage Specification Tool & consider timetable first as this is the easiest to change. Infrastructure should be the last option considered.

The output required from that modelling work is a report detailing:

  • How the work was done
    • Assumptions
    • Risks and opportunities
    • Range of options and capability delivered defined as train service outputs with a focus on non infrastructure options before infrastructure options.
    • Capability required of each intervention within a concept solution

This drives the solution by specifying the capability of the interventions necessary to create a concept solution to drive a system capability change.

Refer back to hierarchy in the Early Stage Specification Tool and consider the following questionsfor effective development:

  1. Can the output change be delivered now with the network as it is, simply by changing the timetable which may of course be a complex exercise?
  2. Are there any trade-offs in train services that will allow delivery of the output change with the network as it is by changing the timetable?
  3. Can the output change be delivered through a change in rolling stock alone?
  4. Does the output change require us to change the infrastructure?

Even at this step the emerging information may mean that it is time to reconsider whether rail is still the appropriate mode when taking account of potential costs. As the scale of the challenge starts to be understood a high-level view of whether a heavy rail option has a chance of passing a value for money test should be emerging.

If this looks unlikely or there are other modal opportunities that may offer a better strategic fit then it may be time to revisit the multi modal assessment tool or to implement your exit strategy.

Step 4: The transition to infrastructure

Concept solutions

Having identified that the requirements can only be met by changing the infrastructure there are some additional steps to undertake before initiating a project. In order to progress meaningfully the next stage is to develop Concept Solutions and the accompanying relevant products.

This will allow some viability and feasibility discussion to take place in a level of detail that allows high level evaluation of whether the idea should become a project for further development and design.

It is recommended that:

  • Aim is to size and scope appropriate solutions to meet the capability set out in the modelling report.
  • Solution should be drawn up only in sufficient detail to confirm scope, show impacts and allow high level order of magnitude (OOM) costings for the necessary work to be derived.
  • Concept solution be an assured product in itself having gone through the necessary/appropriate engineering checks.
  • The aim is to create appropriate concept solutions.  Appropriate solutions brings together the funders conditional requirements, the surrounding conditions and a view of the best application of standards to achieve value for money solutions. 
  • Drawings only need to be in sufficient detail to allow the scope to be understood.
  • Once the funder has selected the options to proceed into development that the concept solutions can simply be moved forward to a greater depth of development and engineering without redoing the work that has already been done.
  • The impacts of the concept, ITSS, analysis and modelling should be tested to examine the whole life impacts on the network and train operations so that judgements can be made about potential trade-offs
  •  Consolidated Risk and Assumptions logs be created

Assumptions and exclusions are often made at this stage because there is still uncertainty or a high number of unknown factors. Funders should take care to understand how these relate to the maturity or uncertainty of the stage.

The concept capture tool can be downloaded here.