Real-World Combustion Emissions, Engine Size and Vehicle Mass Versus Euro-Class Access Criteria in Low-Emission Zones

Low-emission zones, known in Poland as clean transport zones, grant or deny access according to a vehicle’s Euro standard, age and fuel. These administrative labels, however, are only loosely connected to what an internal combustion engine (ICE) actually emits on the road. The founding assumption of a Euro-based zone is that the Euro stage is a usable proxy for the mass a vehicle emits, so admitting newer classes lowers the fleet emission inventory, the activity-weighted sum of class emission factors defined as the product of fleet frequency, in-zone activity and emission factor. This paper tests that assumption directly. A paradox follows: a newer, compliant, large and heavy vehicle can release more carbon dioxide (CO₂), nitrogen oxides (NOx) and particulate matter (PM) than an older, smaller vehicle that the same rule turns away. We develop a reproducible emission-accounting framework that pairs real-world emission factors, resolved by Euro standard, fuel, engine displacement and mass, with a mass-dependent treatment of non-exhaust particles. Given the number of petrol, diesel, liquefied-petroleum-gas (LPG) and electric vehicles in a fleet and the areas of the city and the zone, the model returns daily emissions and their density per square kilometre before and after a rule is applied. For a fleet parameterised on Polish statistics, the Warsaw and Kraków criterion removes about 80% of zone NOx, because the oldest vehicles are also the high-NOx diesels; the same rule, however, removes only about 40% of CO₂ and 48% of PM, and it shifts the admitted fleet toward heavier vehicles that produce more non-exhaust PM. Emission-based, fuel-based and hybrid criteria deliver larger and fairer reductions at the same level of stringency. Aligning zone access with real combustion emissions is therefore both more effective and more equitable, and it supports the wider goals of sustainable, low-carbon urban mobility.