A more conservative system for marking the fuel efficiency of cars will be introduced next year as mileages are often exaggerated under the current system based solely on city driving test results, the Ministry of Knowledge Economy said Tuesday.

The new mileage system will be based on the U.S. 5-cycle testing, which includes a highway driving test, a cold temperature operation test, a high acceleration/quick acceleration test, an air conditioning test in addition to a city driving test, to better approximate actual performance.

Fuel economy labels on cars rolled out from next year will show fuel efficiency not just in city driving but also in highway driving and a combination of both.

Reports have showed that there is a 20 percent gap between the official mileage and the fuel economy perceived by consumers.

The official mileage of Kia Motors’ compact Morning is 18 kilometers per liter, but when measured under the new system, it goes down by about 30 percent to 12.6 kilometers per liter, according to ministry data disclosed by Rep. Lee Hak-jae of the Grand National Party on the parliamentary committee on knowledge economy.

The Hyundai Avante hybrid’s fuel efficiency is reduced from the officially stated 17.8 kilometers per liter to 12.6 kilometers per liter.

The fuel economy levels, marked in five grades, will be revised so that the threshold for Grade 1, which is for cars that can run 15 kilometers or more on one liter of fuel, is raised to 16 kilometers or more. This way, Grade 1 cars will account for only about 7.1 percent of all vehicles produced here, down from the current 30 percent.

The same rules on fuel economy representation will be applied to electric cars as well.

The new system will apply to all passenger cars and 3.5-ton or smaller trucks newly registered starting next year and to existing vehicles starting 2013, the ministry said.

The ministry also plans to open a website that lists information on the annual fuel costs for cars of different fuel types and engine displacements.

By Kim So-hyun (sophie@heraldcorp.com)