Fleet operators need to focus on driver behaviour if they want to improve mpg rather than relying on car manufacturers, according to Nigel Underdown, head of transport advice at the Energy Saving Trust.

He pointed out that over the past two and a half years average new car CO2 emissions have dropped from around 153g/km to 134g/km which means that fleet operators have had an “immediate win” without having to do anything radical.

But he suggested that fleets have had the “low hanging fruit” and they can no longer rely solely on manufacturers to do the work for them.

“One manufacturer has gone public and said ‘we’re getting to diminishing returns’,” Underdown said. “It’s going to get more difficult if you focus on the metal to get improvements in fuel economy. If you’re under pressure to produce cost savings you’ve got to look at the driver.”

Underdown pointed to research carried out by TNO in Holland which shows that real world mpg figures are far below official figures.

Based on a sample of 240,000 vehicles it shows that cars emitting 160g/km, with an official combined mpg figure of 45, actually achieve 35mpg (18% less), cars emitting 130g/km achieve 22% less and 100g/km cars achieve 29% less.

“I’m not suggesting that you stop buying low CO2 cars,” Underdown added. “There are lots of good reasons to buy them, such as lower tax and national insurance, and they are still more efficient. They are just not quite as efficient, probably, for your average fleet driver as you might expect.”

Underdown said that getting drivers to “drive better” needs “leadership from the top” and that the fleet manager’s role is to present the business case for change.