Look up accurate vehicle emissions from registration number in the DVLA database
Rather than using DEFRA factors, it is possible to access the DVLA database to get accurate emissions levels for a specific vehicle based on its registration number.
This would allow for more accurate calculations, and avoid the issue of users having to work out what DEFRA size band their vehicle falls into.
We’re considering this suggestion.
We need to review whether the DVLA figure takes account of real-world driving and vehicle maintenance patterns etc (as is covered by the DEFRA model) or whether it is the manufacturer’s plated emissions. It may be a more accurate benchmark for comparing vehicles, but a less accurate figure for long term emissions calculations?
This integration would add a reasonable amount of complexity both for the system and for users, and may add ongoing costs, so we’ll need to hear from users how useful it would be to them.
As a possible variation on this, it's also been suggested that users could input their actual mpg from their car's trip computer - though we'd need to review how accurate that is (in particular, over what time frame the car calculates the average).