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 .