The Department for Transport (DfT) has published a new technical note on estimating carbon emissions from road users, offering an independent comparison of different carbon estimation methods used in transport appraisal. The note, commissioned by the DfT and prepared by WSP, examines methodological differences, data requirements, and the implications for appraisal practice. 

The technical note reviews three core approaches for estimating road transport carbon emissions: 

• Emissions Factors Toolkit (EFT)- a link-based method using detailed emissions factors. 
• Transport User Benefit Appraisal (TUBA)- a matrix-based approach widely used in transport appraisal. 
• TAG-based bespoke methods- tailored analyses drawing on Transport Analysis Guidance (TAG) conventions. 

The note identifies how methodological choices can influence carbon outcomes and highlights strengths and limitations of each approach, particularly when modelling changes in traffic conditions or speed. 

Accurate carbon estimation remains central to achieving net zero targets and supporting robust appraisal of transport schemes. This technical note does not set policy, but it offers practical clarity to transport professionals, planners and modellers on why different tools may produce divergent results and what that means for carbon accounting in appraisal. 

CIHT members involved in transport modelling, appraisal and climate action are encouraged to review the technical note to help inform appraisal practice and support more consistent carbon reporting in project evaluations.