Research and analysis

Estimating carbon emissions from road users

A technical note reviewing different methods for estimating carbon emissions from road users.

• From: Department for Transport
• Published: 29 January 2026

Documents

Technical note: estimating carbon emissions from road users

PDF, 2.75 MB, 35 pages

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Details

This technical note reviews 3 methods for estimating road user carbon emissions in line with the Department for Transport’s (DfT’s) guidance:

• the emissions factors toolkit (EFT)
• transport user benefit appraisal (TUBA)
• a bespoke transport analysis guidance (TAG) based approach

It looks at the assumptions, data and calculations behind each approach to see why their results differ and what that means for how the project is assessed.

Overall, the review found that methods based on individual road links tend to show more accurately how changes in speed affect fuel use, and therefore carbon emissions.

It also found that TUBA, which uses averaged, matrix-based calculations, can produce counter-intuitive results when estimating carbon impacts. In some cases, its approach can suggest environmental benefits where none actually exist.

This technical note was commissioned by the DfT and authored by WSP.

Published 29 January 2026