A vehicle comprises a compression ignition engine provided with engine management means and having a catalyst for exhaust gas aftertreatment, wherein the engine management means is configured, when in use, to detect idle conditions and upon determining that idle conditions exist, stops the engine entirely, wherein the catalyst comprises a honeycomb substrate monolith coated with a catalytic washcoat comprising one or more precious metal, which catalytic washcoat being arranged between a first, upstream washcoat zone and a second, downstream washcoat zone, wherein a thermal mass in the first washcoat zone is different from a thermal mass in the second washcoat zone and wherein a washcoat layer in the first, upstream washcoat zone is substantially contiguous with a washcoat layer in the second, downstream washcoat zone.