Overview

Scot-TAG, which is an acronym for Scottish Transport Analysis Guide, is intended to provide transport practitioners working on Scottish based transport projects, or any other interested party, with access to the latest information and guidance that they will need when developing and assessing transport schemes and strategies.

Scot-TAG serves as the gateway to:

as well as general Scottish Government and Transport Scotland transport assessment advice.

Read the Scot-TAG frequently asked questions

Scot-TAG links

Links to relevant websites:

Contact / Register

For general enquiries please contact us at: Scot-TAG@transportscotland.gsi.gov.uk.

To receive automatic e-mail notification of updates to Scot-TAG, including quarterly updates related to Scottish Transport Appraisal Scottish (STAG), you can register your details with our free newsletter subscription service.  Please note, you should select the Scot-TAG newsletter option only if you do not wish to receive e-mail alerts on other Transport Scotland news.

Scottish Transport Appraisal Guidance (STAG)

Scottish Transport Appraisal Guidance (STAG) consists of two parts:

  1. Stag guidance
    Best practice in transport appraisal
  2. Technical database
    Detailed guidance on the methodology and reporting structure to be used when completing a STAG appraisal

The communication of future updates, known as Business as Usual updates, will be made available through the Technical Database. The overarching principles as set out in the Guidance remain the same and are not subject to regular updates.

The Guidance supports the Scottish Government’s objectives by providing a clear framework to assess evidence based transport problems and opportunities. It does so by promoting robust, objective-led analysis that can be consistently applied in all transport appraisal contexts.

STAG is one process comprising four phases – Pre-Appraisal, Part 1 Appraisal, Part 2 Appraisal and Post Appraisal – and should be applied proportionally but comprehensively, with the level of detail determined by the scale of the transport challenges under consideration. The principle of being objective-led, rather than solution-led allows the appraisal of options against Planning Objectives, STAG Criteria and establish policy directives, and provides a robust evidence base for decision makers. Any final report must also include proposals for robust monitoring and evaluation plans.

A robust transport appraisal provides evidence to decision makers on transport investement. In Transport Scotland, a transport appraisal undertaken in accordance with guidance can provide the Strategic Business Case for investment. A business case provides the documentation with the reasoning and justification of a scheme. In order to satisfy this, the Office of Government Commerce and HM Treasury have laid out a four stage process that should be followed in the development of business cases. The stages are:

  • Stage 0 - Business planning: Strategic Outline Plan (SOP)
  • Stage 1 - Scoping: Strategic Business Case (SBC)
  • Stage 2 - Planning: Outling Business Case (OBC)
  • Stage 3 - Procurement: Full Business Case (FBC)

STAG guidance should also be referred to when undertaking an Outline Business Case, during which the 'Strategic' case and the 'Socio-Economic' case are revisited.

More details on the development of business cases for Transport Scotland can be found within the following publication, Guidance on the development of business cases in Transport Scotland.

For help and advice on the application of this Guidance, please email the Scot-TAG Mailbox or use the Contact Us link. To receive automatic e-mail notification of updates to Scot-TAG you can register your details with our free newsletter subscription service. Please note, you should select the Scot-TAG Updates option only if you do not wish to receive e-mail alerts on other Transport Scotland news.

Practitioners should note that superseded versions of STAG are available in the Archives.

Business as usual updates

Updates published July 2017

New section 9.3 Wider Economic Impacts guidance, which replaces sections on Wider Economic Benefits and Economic and Location Impacts

Updated section 9.4.7 Price Base Year, which includes revised guidance on which price base to use

Updates published September 2016

Updated Section 9.5.14: Vehicle Occupancies. This update brings STAG table 9.10 (car occupancies) up to date with WebTag table A1.3.3 (Dec ’15 version).

Updated Section 9.5.18: Vehicle Operating Costs (fuel and electricity). STAG tables 9.17 & 9.18 have been updated to match WebTag tables 1.3.12 & 1.3.13 (Dec ’15 versions) as per latest DECC fuel price outturn/forecasts and fuel efficiency parameters.

Updated Section 9.5.19: Rates of Change in Fuel VOCs. STAG table 9.23 shows forecast average vehicle fuel/energy cost formulae parameter values and has also been updated to match WebTag tables 1.3.12 & 1.3.13 (Dec ’15 versions).

Updates published 30 November 2015

Updated Section 1: How the phases of STAG fit together. This update includes reference to the “Guidance on the development of businesses cases in Transport Scotland”. (Section 1.1.4) Some changes in terminology are also included.

Updated Section 8.2.1: Assessment of Road Accidents. Updated guidance on the use of the NESA manual.

Updated Section 16: Evaluation. This update introduces a reference and link to the Rail Evaluation guidance.

Updates published 30 April 2015

Updated Section 7.4.2. Non-traded values (£) per tonne of CO2. This update provides updated values to remain in line with values publishing in WebTAG data book Table A3.4.

Updated Section 7.4.11: Enhancing guidance on Appraisal of Active and Sustainable travel interventions.

Update to Section 9.5.8. Fuel/energy consumption formulae parameter values. This update provides updates values to remain in line with values published in WebTAG data book table A1.3.8.

Updated Section 9.5.6. Indirect Tax Revenues. This update provides further clarification of indirect tax revenues.

Updated Section 15.2.1: Refreshed text for monitoring for active and sustainable travel and smarter choices interventions

Updates published 30 January 2015

Updated to Driver Frustration. This update provides guidance on monetising driver frustration impacts in line with research undertaken as part of the A9 Dualling Programme Strategic Business Case. Refer to Sections 5.4.3, 9, 9.2.2.8.

Updated Section 6 Introduction to Part 2 Appraisal. This update provides an enhancement to the text to allow for broader use of Bespoke Values of Time where appropriate.

Update on Reporting. This update provides enhanced guidance on scoring against the seven point scale and the use of stakeholder engagement in option sifting. Refer to Sections 2.7, 3.7, 4.5, 5.4, 5.8, 5.9 and 14.1

Updated Section 9.2.1 Principles of TEE Analysis. This update provides clarification on the Rule of Half.

Updates published 30 May 2014

The following changes have been made to the STAG Technical Database following the latest meeting of the STAG Steering Group. These changes are effective from 30 May 2014. Superseded sections of the Technical Database are available at the Archive.

Updated References to WebTAG: This update follows a full audit of references to the Department for Transports WebTAG following the publication of their fully revised guidance in January 2014. This applies to Sections 7, 9 12 and the Environment Worksheets.

Updated Section 7.4.3 Local Air Quality. This update provides guidance on monetising local air quality impacts in line with new economic values published in WebTAG.

Updated Values of Time and Vehicle Operating Costs: This update follows change to the base year values in WebTAG, following recent research from ITS Leeds, also to account for latest forecasts of GDP growth and fuel prices and changes to DECC guidance. Refer to Section 7 - Tables 7.3 & 7.4 and 9.5.12

Updated Section 11.2.1 Public Transport Network Coverage: This update provides option and non-use values in line with WebTAG guidance. The evidence around option values is small but relatively consistent in identifying these as legitimate benefits and the results of the various studies to date are comparable. Additionally, these values have been used in the past in STAG appraisals, so it is important for STAG to reflect this.

New section 11.6.4: New entry on the impact of changes to Park and Ride at railway stations on rail demand. An extensive piece of analysis was carried out to cover the gap in research – this update is the result of that analysis, and gives suggestions on how changes to price of parking might impact on demand, how changes in supply of parking might impact on demand, and guidelines on how much extending existing car parks might cost. Refer to Section 11.6.4

Updated Uncertainty Analysis (Sensitivity and Scenario Testing) to replace Sensitivity Analysis: This update aims to clarify the various model tests which may be undertaken to produce a ‘range of forecasts’ e.g. sensitivity testing, scenario testing, uncertainty testing, and option testing. Refer to Section 13.6

Updated Section 17 Additional Information: This update provides rationalisation and update of the references in the chapter and simplification of the Modelling and Assessment Software section. Refer to Section 17 and some associated reference changes in Sections 2, 7 and 16 also.

New Economy Spreadsheet: This spreadsheet has been prepared to support Section 9 Economy and provide the data held in Table 9.7 to 9.25 in a more user friendly manner. Refer to Section 9.5.12 and Section 17.1

Updates published 20 December 2013

The following changes have been made to the STAG Technical Database following the latest meeting of the STAG Steering Group. These changes are effective from 20 December 2013. Superseded sections of the Technical Database are available at the Archives page.

  • Updated References: This update follows a full audit of references and includes minor corrections and updates to hyperlinks, citations and addition of sources where not previously indicated. This applies to the majority chapters of the Technical Database.
  • Update to Journey Time Reliability: This update is intended to give clarity on existing guidance and to suggest some data sources for journey time reliability appraisal. Refer to Sections 2.3 2.4.1 and 9.2.2.9
  • Update to include Policy Assessment Framework (PAF): PAF is a tool designed to improve the assessment of options against the ‘Integration’ criteria of STAG. This update applies to Section 5, Section 10 and Section 14. The PAF spreadsheet and guidance notes.
  • Update includes Improvements to the Reporting and Use of Appraisal Summary Tables (ASTs): This update aims to provide greater consistency and clarity in the reporting of appraisals. Refer to Section 5.9. and Section 14.
  • Update to Treatment of Sunk Costs: This update restates the position of reporting Sunk Costs in STAG in light of recent reports by Audit Scotland. Refer to Section 12, specifically Section 12.2.
  • Updated Evaluation Guidance: This update has been prepared to reflect recent work undertaken on improving guidance on the evaluation of projects. Refer to Section 16.
  • Updated Software References: This update ensures that references to modelling programs used to support appraisal are correct and up to date following changes to version and ownership. Refer to Section 17, specifically 17.3.3.3.

Updates published 19 November 2012

The following changes have been made to the STAG Technical Database following the latest meeting of the STAG Steering Group. These changes are effective from 19 November 2012. Superseded sections of the Technical Database are available at the Archives page.

Updated Value of Time Growth Rates

Updated value of time growth rates to reflect the UK Budget 2012 GDP forecasts. Details are available here.

Updated Base Year for Appraisal

The price base year and base year for discounting have been updated to 2010. Values throughout the STAG Technical Database have been updated to 2010 prices.

Updated Indirect Taxation

The average rate of indirect taxation is now 19.0% rather than 20.9%. Details are available here.

Updated Vehicle Operating Costs

Vehicle Operating Costs have been updated to take into account the introduction of electric cars to the car fleet. Details are available here.

Updated Rail Demand Growth Cap

The rail demand growth cap has been updated to 2032. Details are available here.

Updates published 23 April 2012

The following changes have been made to the STAG Technical Database following the latest meeting of the STAG Steering Group. These changes are effective from 23 April 2012. Superseded sections of the Technical Database are available at the Archives page.

Updated Value of Time Growth Rates

Updated value of time growth rates to reflect the UK Budget 2011 GDP forecasts. Details are available here.

Updated Carbon Values

The carbon values have been updated to reflect the new, robust approach to valuing emissions by the Department of Energy and Climate Change. Details are available here.

Indirect Taxation

A change in the treatment of indirect taxation in the calculation of the benefit to cost ratio, BCR. Details are available here.

Updates to web links and contact details

Web links and contact details have been updated throughout the Technical Database where appropriate.

Vehicle Operating Costs (fuel)

The fuel consumption equation has been revised to improve the relationship between speed and fuel consumption, especially at low speeds. Details are available here. This section has also has been updated to reflect the UK Budgeet 2011.

Latest Travel Demand Forecasts

Section 9.2.2.2 has been updated to recommend the use of the Scottish Trip End Programme (STEP) and/or TEMPRO in establishing baseline travel demands for modelling and appraisal purposes.

Recording Travel Time Savings by Size

A change in the treatment of indirect taxation in the calculation of the benefit to cost ratio, BCR. Details are available here.

Equality Impact Assessment (EQIA)

The Technical Database has been updated to provide a fuller understanding of EQIA, its applicability to transport appraisal and its implications. Details are available here.

Worksheets and Spreadsheets

An updated version of the Carbon Monetisation Spreadsheet has been provided so as to include the updated carbon values. The Part 2 Appraisal Summary Table has also been updated. The documents are available here.

Updates published 15 December 2009

The following changes have been made to the STAG Technical Database following the meeting of the STAG Steering Group on 13 November 2009. These changes are effective from 15 December 2009. Superseded sections of the Technical Database are available at the Archives page.

Establishing Do-Minimum and Reference Case Scenarios

Revised guidance is provided on the treatment of uncertainty in model forecasting. To assist in the preparation of a do-minimum and reference case, factors influencing demand, supply and cost of travel should be analysed and used to construct an uncertainty log. Details are available here.

Additional related guidance on sensitivity testing to reflect the new do-minimum and reference case guidance is provided in Section 13.6 Sensitivity Analysis.

Embodied Carbon Impacts of Transport Appraisal

New guidance is provided on assessing the CO2 emissions associated with the construction of transport infrastructure. This guidance forms a new subsection of existing Global Air Quality guidance. Details are available here.

Reliability Benefits

A methodology is being introduced for assessing the reliability benefits associated with a transport intervention. This is based on measuring improvements in journey time variability. Details are available here.

The treatment of quality is unchanged but guidance is now provided separately in Section 9.2.2.8. Details are available here.

Scheduling Costs

Revised guidance is introduced to incorporate scheduling costs into the calculation of value of time impacts. The inclusion of scheduling costs will be especially important when appraising changes to ferry services. Details are available here.


Wider Economic Benefits - WB3, Increased Output in Imperfectly Competitive Markets

Guidance on WB3 – increased output in imperfectly competitive markets – has been updated to recommend an uplift factor of 20% is used in rural appraisal. This reflects recent evidence demonstrating higher cost price margins in rural areas. Details are available here.

Updates published 1st April 2009

The following changes have been made to the STAG Technical Database, following the meeting of the STAG Steering Group on 5th March 2009. These changes are effective from 1st April 2009. Superseded sections of the Technical Database are available at the Archives page.

Introduction of Walking and Cycling Guidance

Guidance is being provided for appraising walking and cycling schemes. The methods for physical fitness are described in Section 7.4.11 and related guidance can be found in the following areas:

  • Section 8 Accidents and Security; and
  • Environmental worksheets and Appraisal Summary Tables, available from the downloads section.

Updated fuel price forecasts

Sections 9.5.18 and 9.5.19 have been updated to reflect the latest fuel price projections by the Department for Energy and Climate Change (DECC). Details are available here.

Indirect taxation impacts for rail schemes

Section 9.5.22 Rail Operating Costs has been updated to include guidance on the calculation of taxation impacts associated with rail schemes. Details are available here.

Land-Use and Transport Integration in Scotland (LATIS)

Changes have been made to the Technical Database to reflect the launch of the new LATIS service. Details are available here.

Updates published 5th December 2008

The following changes have been made to the STAG Technical Database, following the meeting of the STAG Steering Group on 18th November 2008. These changes are effective from 5th December 2008. Superseded sections of the Technical Database are available at the Archives page.

Section 9.3.6 Reporting of Wider Economic Benefits

Further guidance has been provided regarding the requirements for reporting the methodology used to calculate agglomeration benefits. Details are available here.

Section 9.2.2.1 Benefits to Transport Users and Section 9.5 Appraisal Parameters

These sections have been updated to provide guidance on the calculation of road network effects in rail schemes. Details are available here.

Worksheets and spreadsheets

An updated version of the Agglomeration Spreadsheet - General Version has been provided to simplify agglomeration calculations in the absence of a detailed zonal model. The spreadsheet is available here.

Updates published 4th September 2008

The following changes have been made to the STAG Technical Database, following the meeting of the STAG Steering Group on 18th August 2008. These changes are effective from 4th September 2008. Superseded sections of the Technical Database are available at the Archives page.

Section 4.1.1 Do-minimum and reference case

An addition has been made to the text to clarify that, for an transport improvement to be included within the do-minimum, policy or funding commitment must come from the body responsible for changing any asset which will be affected. Details are available here.

Section 9.5.18 Vehicle operating costs (fuel) and Section 9.5.19 Rates of change in fuel VOCs

These sections have been updated to reflect the latest fuel price projections by the Department for Business, Enterprise, and Regulatory Reform (BERR). Details are available here.

Section 9.3.1 Agglomeration economies

This section has been updated to provide guidance on when transport schemes are likely to have the potential for agglomeration economies. Previous guidance within Section 9.3.1 on the calculation of agglomeration economies can now be found in Section 9.3.5 Calculation of Wider Economic Benefits. Details are available here.

Section 17.3.5 Accessibility Modelling

The list of accessibility models in Table 17.8 has been updated. Details are available here.

Updates published 27th May 2008

As part of the STAG Refresh, the following Business as Usual updates have been made to the STAG Technical Database:

  • Monetisation of carbon;
  • Introduction of Wider Economic Benefits;
  • Guidance on the application of Optimism Bias; and
  • Changes to reporting and indicators.

This guidance is effective from 28 May 2008 and should be applied to all new transport projects being appraised in accordance with STAG. A new project is defined as one including a first application for funding under STAG.

Monetisation of carbon

In line with UK guidance on climate change, the value of all carbon emissions must now be reported. Further detail is available in Section 7.4.2.

Introduction of Wider Economic Benefits

This introduces new guidance on how to capture the impacts of transport schemes on economic output and productivity. Further detail is available in Section 9.3.

Guidance on the application of Optimism Bias

This provides clear guidance on the treatment of risk and uncertainty. Optimism Bias should now be applied to both capital costs and risk assessment, meaning that there is no need for a contingency allowance. Further detail is available in Section 13.3.

Changes to reporting indicators

A new summary table has been introduced, which summarises an option's impact against all the STAG Criteria and the Government's Purpose. New indicators have also been introduced for each criterion which reports monetary impacts, but the BCR and NPV remain the key indicators. Further detail is available in Section 12.7.

Network Evaluation from Survey and Assignment (NESA)

NESA is a computer program developed and maintained by Transport Scotland that is used to assess proposed road schemes, measuring their impact on traffic and the economy in the surrounding area.

Contacts

For all general NESA inquiries, plus support etc., users should email: LATIS@transport.gov.scot or write to:

Technical Analysis Branch
Transport Scotland
Buchanan House
58 Port Dundas Road
Glasgow
G4 OHF
 

Program Availability, NESA Manual and Guidance Documents

A copy of the executable NESA file can be obtained by emailing your request to LATIS@transport.gov.scot

The program will be issued on CD-ROM together with an electronic copy of the most up to date NESA Manual (as a PDF).

Program for the Economic Assessment of Road Schemes (PEARS)

PEARS is an economic assessment package, developed and maintained by Transport Scotland, that has been specifically designed for use with the output from traffic microsimulation models to assess the economic impacts of proposed road schemes.

PEARS carries out trip-based assessments of changes in travel time costs and vehicle operating costs. The costs of a trip-based assessment are derived by aggregating the costs of each individually modelled vehicle on the network.

It is a requirement in Scotland to use microsimulation traffic modelling combined with PEARS to model / assess WS2+1 schemes to ensure that any downstream benefits are captured.

Program Availability, Guidance Documents & Support

To obtain a copy of the PEARS program, plus associated documentation etc., users should email: 

LATIS@transport.gov.scot or write to:

Technical Analysis Branch
Transport Scotland
Buchanan House
58 Port Dundas Road
Glasgow
G4 OHF

The program will be issued on CD-ROM together with an electronic copy of the most up to date PEARS User Guidance and other documentation (as PDFs).

The documentation can also be downloaded directly from the PEARS website.

Analysis of Instantaneous Road Emissions (AIRE)

AIRE is an ancillary software module specifically designed to post-process the outputs from traffic microsimulation models and calculate vehicle emissions.

AIRE takes outputs from microsimulation models for individual vehicles at each simulated time-step, typically twice a second, and estimates the tailpipe emissions based on their current speed and acceleration.  The module uses detailed Instantaneous Emissions Modelling (IEM) factors derived by TRL using the Passenger car and Heavy Duty Emissions Model (PHEM) developed by the Technical University of Graz.

AIRE can be used to process the detailed, vehicle by vehicle outputs produced by microsimulation models for each simulated time step and provides significantly more disaggregate and detailed emissions estimates compared with traditional, average speed-based methods.  AIRE rapidly processes the outputs from multiple simulation runs and produces estimates of the oxides of nitrogen, particulate matter and total carbon that result from the combustion of fuel throughout each simulated vehicle’s journey.

Program Availability, Guidance Documents & Support

To obtain a copy of the AIRE program, plus associated documentation, users are directed to the AIRE website.

The program will be issued on CD-ROM together with an electronic copy of the most up to date AIRE User Guidance and other documentation (as PDFs).

The documentation can also be downloaded directly from the AIRE website.

Contacts

AIRE is developed and maintained by SIAS Ltd., in collaboration with the Transport Research Laboratory, on behalf of Transport Scotland.

For all general AIRE inquiries, plus support, and to register as an AIRE user, please email: aire-support@sias.com