Reducing vehicle air pollution could prove to be an increasingly difficult challenge as driving habits are making many of the technological advances ineffective.

The latest analysis of the EQUA Index data by Emission Analytics shows that the average daily distance driven in passenger cars is not sufficient for a vehicle’s pollution control system to warm up and become fully functional. The resultant high levels of cold start NOx emissions, from both petrol and diesel engines, could provide an additional challenge for urban air quality initiatives such as proposed Clean Air Zones.

According to the UK Department for Transport more than half of car driver trips nationally are under 5 miles. For the majority of vehicles tested by Emissions Analytics, it can take more than five minutes for after-treatment systems to reach operating temperature.

Petrol engines suffer proportionally much more from cooler exhausts although produce less NOx in absolute terms, whereas the diesel engines have a 29% uplift in NOx when the exhaust temperature is lower.