Diesels’ Removal Linked to Cleaner Air, Fuel Savings

Replacing all the diesel-powered cars in the U.K. more than 10 years old with the latest models could save 207 million gallons (173 million U.K. gallons) of diesel fuel a year.

The figure was reached by researchers for service and repair company Kwik Fit, who crunched the numbers using U.K. government vehicle statistics and based their results on a national scrappage scheme that would see the older diesel vehicles permanently removed from the road.

They found U.K. motorists are driving 30.2 billion miles (48.6 billion km) a year in about 3.5 million diesel cars – an average of 8,676 miles (13,970 km) each – that were first registered in 2007 or before.

With average fuel economy rising over the past decade, if these journeys were made in new diesel cars, drivers’ total savings on fuel costs would be about £947.8 million ($1.27 billion) a year.

There also would be a reduction in heavy-truck traffic, as the fuel saving is equivalent to more than 20,700 full loads of the largest fuel tankers, which carry 10,000 (U.S.) gallons each.

Additionally, there would be a significant drop in emissions as the older cars that at best meet Euro 4 emissions standards would be replaced by those meeting Euro 6 requirements.

Nitrogen oxide (NOx) emissions would fall 68% to 8.5 million lbs. (3.9 million kg), while particulate matter would fall 80% to 529,110 lbs. (240,000 kg).

The Kwik Fit researchers believe the improvement in real-world performance over the past decade means these figures are a conservative estimate of the potential reductions in emissions. That’s because the analysis is based on all the older diesels being replaced by cars with new diesel engines, whereas many in fact would be swapped for electric or hybrid-electric vehicles.

An earlier study by Kwik Fit found only a third of diesel owners would buy another diesel vehicle when they replace their current model. With many drivers indicating they might switch to gasoline, the researchers assessed the impact of swapping diesels over 10 years old for new gasoline models.

In this scenario, there would be an even greater reduction in emissions over the same mileage, with the level of NOx falling 20.3 million lbs. (9.2 million kg), while the drop in particulates would be the same as with a switch to new diesels.

However, there would be a tradeoff as there could be a 53.6 million-lb. (24.3 million-kg) increase in the level of carbon monoxide (CO) emissions, due to the CO limits on gasoline engines being higher than for diesel.

Kwik Fit Communications Director Roger Griggs says the cost of replacing all diesels more than 10 years old with new models, assuming an average new-car price of £28,000 ($37,480), would be more than £97.3 billion ($130.2 billion).

“Currently, this cost would be borne solely by the individual motorist,” he says in a statement. “Any incentives the government can give the private individual to move to more efficient vehicles could have a significant impact.”