DfT reveals transport analysis priorities

The DfT has outlined the priority areas for action to improve its transport analysis guidance (TAG), following a consultation last summer (LTT 22 Jun 18). Here we summarise the main action areas

The DfT’s new document, Appraisal and modelling strategy: informing future decisions, outlines the Department’s priority areas of work to improve the quality of transport analysis for decision-making. The work is grouped under five themes as follows:

People and place 

Quick wins:

Locational attractiveness and urban realm: a scoping study will explore options for new guidance on incorporating locational attractiveness and urban realm into appraisal. The DfT says the consultation revealed “almost universal consensus that a step-change in the ability of appraisals to capture location attractiveness impacts, with a particular focus on valuing the urban realm, was needed”.

Landscape impacts: the DfT will assess how it can incorporate new evidence/values and move to the ‘ecosystem services’ approach. Research has recently been completed into incorporating an ecosystem service-based valuation of landscape impacts into transport appraisal guidance (TAG). The report, which will be published soon, recommends a number of ecosystem services for immediate incorporation into TAG, such as carbon sequestration (reducing greenhouse gases in the atmosphere), recreation, vegetation, mitigation of noise and air pollution and visual amenity. However, there remain a number of areas for further research, such as biodiversity, ‘viewsheds’ (the areas visible from a given location) and cultural heritage. Rule of half: a scoping study will consider how to capture transport benefits in appraisal under a scenario of land-use change.

Sustained development activities:

Active travel modes: research will be commissioned to broaden the coverage of active modes in appraisal guidance. “This could cover better appraisal of cycle lane infrastructure appraisal, forecasting active travel trip generation and active travel health benefits,” says the DfT. The Department will continue to engage with a cross-Whitehall scoping study to review values of life and health.

Social impact appraisal: a joint scoping study with Highways England will identify areas for improvement in social impact valuation. 

Values of time: a rolling programme of updates will be made to values of time. The Department is also keen to  improve understanding of values of time in congested conditions. Research will be conducted into the values of time for modelling and appraisal under new technology scenarios, such as the wide-scale roll-out of connected and autonomous vehicles (CAVs) or Mobility as a Service (MaaS).

Freight appraisal: research to update key appraisal values.

Distributional impacts: the DfT wants to promote greater use of distributional analysis in appraisal. 

Areas for further consideration:

Valuing the customer experience: the DfT is collaborating with Highways England on research into the value of information, road layout and surface quality.

Resilience: research will examine extreme disruption events not captured by current reliability appraisal methods.

Wellbeing review: a review of wellbeing-based approaches in transport appraisal is proposed.

Uncertainty over the future of travel

Quick wins: 

Uncertainty toolkit: a scoping study will be undertaken to identify the content of an ‘uncertainty toolkit’ for proportionate and consistent application in appraisal. “Given the wide support for an uncertainty toolkit, we will commit to producing a prototype over the next two years,” says the DfT. “As there was less agreement as to what the toolkit should cover and the level of ownership that DfT should take around national level [travel] demand, we will begin this piece of work by developing a scoping study to determine what is best to include in the toolkit.”

Scenario development: in-house piloting will develop an understanding for how scenarios can be used to deal with uncertainty. “We shall consider how best to incorporate uncertainty analysis into our existing tools and products, most notably the travel demand forecasts provided by the National Trip End Model, which provides travel demand projections for use in appraisals across the country,” the Department explains. “Providing more scenarios of these data, including clear guidance on how they are expected to be used, would provide greater consistency in appraisals.”

Optimism bias: the DfT has begun a research project to improve the evidence base for optimism bias adjustments, looking at historical evidence regarding cost overruns on different types of projects and different areas of cost, including maintenance and operating costs as well as capital costs. 

Sustained development activities: 

Tools for early testing of uncertainty: the Department will examine using simpler modelling approaches to test uncertainty at earlier stages in project development.

Research drivers for uncertainty: research will continue into the impact of behaviour change and new technologies, such as electric and autonomous vehicles.

Case studies: case studies will be published that highlight good examples of incorporating scenarios into appraisal.

Transformational investments & housing

Quick wins:

Cross-sector package appraisal: the Department will complete work reviewing current appraisal methods.

Review and update current methods: the Department will “review, undertake new collaborative research and update existing appraisal methods”.

Historical case studies: a scoping study will identify potential schemes and different approaches to building up historic case studies on economic transformation, and sustained development.

Sustained development activities:

Local economic impacts: The DfT will review approaches such as distributional weights and ways of improving the reporting of local level impacts.

Develop a common framework for local impacts: a checklist of factors/evidence that are critical for a transformational investment to succeed but that can’t be easily modelled, is proposed.

Capturing transformative effects: research will explore the potential for new approaches to capturing non-marginal effects of transport.

Housing and transport appraisal: working with external bodies, the DfT will hold a symposium on sustainable development, review land value uplift and how planning assumptions are treated across different appraisals.

Increasing the availability of data: the DfT will work with external bodies to increase the availability of data to support model development and validation.

Areas for further consideration:

Business and household relocation: research will examine household and business relocation decisions, including the speed and magnitude of the response to changes in the transport system.

Supporting the application of TAG

Quick wins:

Making TAG more accessible: Various initiatives, including case studies to demonstrate proportionate analytical approaches and unpick more difficult concepts. 

Support and training: a TAG annual conference, and DfT-led training courses are proposed.

Sustained development activities:

These include creating a case study repository

Modelling and appraisal tools

Quick wins:

Opening up national modelling tools: The Department will undertake “extensive stress-testing and back-casting” on the National Transport Model, which is used to produce the National Road Traffic Forecasts, and publish the findings. The DfT adds: “Whereas we can open up the models through better documentation and education, simply sharing the core DfT forecasting models in their current form is not a straightforward matter. This is due to various commercial issues, and that they require significant specialism to operate and understand effectively, which DfT cannot directly support. That said, there may be various model components which we could consider making more widely available, such as the National Trip End Model (NTEM) for use in scenario testing.” 

Base year trip matrix development: “The core short-term improvement to modelling guidance we have identified is the introduction of a guidance unit on techniques to build base year trip matrices,” says the DfT. “These are fundamental to a model’s performance and its results. This will include addressing the emergence of big data sources such as mobile network data into guidance, which is currently an omission.” 

Evaluation guidance in TAG: publish guidance for evaluating transport projects and links to appraisal.

Sustained development activities:

Keep forecasting capability up to date: the DfT will review and update recommended multi-modal forecasting parameters and improve the evidence base for walking and cycling forecasting.

Freight modelling: a review of best practice is proposed, together with a research programme.

Enhance trip-end modelling: the NTEM suite will be reviewed, leading to an updated tool, data and guidance. “There are several potential areas to enhance which we will need to decide how to prioritise. These include improving forecasts of car ownership in the National Car Ownership Model, making the scenario development process in the scenario generator more accessible, and enhancing the trip end model to include more explanators for forecasting future trips. A key question here is how to forecast trip ends more accurately where travel behaviour is changing.”

Areas for further consideration

Review and test alternative techniques: the Department will explore innovative methods as part of the national modelling tools, including alternative modelling approaches and the use of emerging and maturing data sources.