Drivers of new cars have been finding that their fuel economy does not meet the manufacturer’s claims, but larger doubts are being raised about the official exhaust tests. We cannot expect these tests to match our own driving styles and the hills and junctions that we encounter every day, but vehicles should not be designed to pass official tests and then work differently on the roads.

Official tests are conducted in laboratories over a simulated route. Alternatively cars can be equipped with complex instruments connected to their exhausts and tested on real roads. Results from 97 journeys in 15 of the most modern diesel cars have been gathered by the International Council on Clean Transport. These cars met the latest European and US standards in lab tests but on the road they emitted, on average, seven times the nitrogen oxides compared with official tests; one car emitted 25 times. On the positive side, other exhaust gases have been well controlled, as have pollutants from petrol cars, but nitrogen oxides from diesels contribute to nitrogen dioxide (NO₂) that is more than twice the EU and World Health Organisation limits in some UK cities. Nitrogen oxides also mix with other pollutants to form harmful airborne particulates and summer-time smog.

By relying on exhaust emissions controls to control urban NO2 our policy makers put all their eggs in one basket rather than controlling the growth in diesel vehicles or promoting walking and cycling. The proposed solution is not tighter limits but better tests. In the meantime we will be waiting longer for clean air in our cities.

via Pollutionwatch: When will exhaust tests get real? | Environment | The Guardian.