RDE
Real Driving Emissions is the on-road test — equipment strapped to the car in real traffic — that backs up the WLTP lab test for NOx and particulates. A diesel that passes RDE step 2 (RDE2) is certified clean in real driving, which is why RDE2 diesels pay standard first-year VED rates while older non-RDE2 diesels pay one band higher. It was introduced after the diesel emissions scandals to make sure lab results hold up on the road.
Example
Nearly all new diesel cars on sale are RDE2-compliant and pay normal VED; pre-2020 diesels often aren’t.