Estimation of road transport emissions from inventory models,
considering different geographical scales [1–3], shows a growing
contribution from vehicle categories such as heavy-duty vehicles
(HDVs) or powered two-wheelers (PTWs). Passenger cars (PC) still
represent the most important category for fleet extension and travelled
mileage, but their real-world emission factors have been
forced to strong reductions by the development of the relevant legislation
[4,5], even if on-road emissions may be different from expected
values included in inventory models [6] and a careful
evaluation of available methods for emission factors definition is
requested [7]. Comparisons with HDVs and PTWs are therefore
generally advantageous for PCs, when taking into account equivalent
emission classes [2,8,9].