Real-world fuel consumption of passenger cars
In recent years, the fuel consumption of passenger cars has gone down. The decrease in fuel consumption when driving the car on the road is, however, less marked than the decrease in fuel consumption as measured during type approval testing. In fact, the difference between real-world consumption and that stated in brochures has widened in recent years. This is shown in studies in which TNO has been monitoring the real-world fuel consumption of passenger cars. The reports from these studies can be found on this page.
According to the type approval test values, the average fuel consumption of new passenger cars in the Netherlands has fallen by 30% since 2000. However, consumption in practice is higher than what car manufacturers claim in their brochures. On average, new cars use around 30 to 50% more fuel than they do during tests. This means consumers purchasing a fuel-efficient vehicle save less than expected on fuel costs.
There is a direct link between fuel consumption and CO2 emissions; cars that use more fuel emit more CO2. The difference between real-world and type approval levels of fuel consumption means that new cars emit 50 grams more CO2 on average that they do during tests, for every kilometre they cover. This undermines the effectiveness of European and Dutch policies regarding the reduction of CO2 emissions in traffic.
TNO is monitoring actual levels of consumption
Since 2008, TNO has been investigating, on behalf of Travelcard Nederland BV and the Ministry of Infrastructure and the Environment, the real-world fuel consumption of passenger cars. An analysis of fuel pass data of a large and varied group of road-users, made available by Travelcard Nederland BV, has revealed trends in the average amount of fuel consumption.
Causes of the growing difference between nominal and real-world levels
Real-world levels of fuel consumption by a car depend very much on how it is used, such as the loads it carries and the types of journey it makes, as well as the driving style of the driver. Weather and traffic conditions also play an important part. Driving patterns during the tests on a roller dynamometer in a lab are not exactly the same as the average driving pattern in practice, and the environmental conditions vary too. In addition, tests of cars on a roller dynamometer do not include energy consumed by auxiliaries, such as lighting or air-conditioning. This means that, in practice, fuel consumption and CO2 emissions are greater than those measured in the tests.
The widening gap between the results from the laboratory tests and real life is caused primarily by the use of various consumption-reducing techniques (such as stop-start systems) that produce greater benefits during the tests than in reality, and by the more prevalent use by manufacturers of so-called flexibilities in the test procedure. By applying margins and ambiguities in the prescribed procedure and test conditions, it is possible to reduce the levels of consumption measured in tests without making technical modifications to the vehicle.
Real-world consumption of plug-in hybrid vehicles
Plug-in hybrid electric vehicles can run on fuel and electricity, which is obtained from the electricity network. When running on fuel, the causes mentioned above lead to a comparable difference between type-approval and real-world fuel consumption in the case of plug-in hybrid vehicles. However, there is an additional factor here - the number of kilometres covered by the vehicles when running on electricity. In practice, this proportion is, on average, significantly lower than during the tests, because many users do not regularly charge up their batteries. This results in a greater difference in fuel consumption and CO2 emissions between the tests and reality than is the case with conventional vehicles. In 2013, under the direction of the Formula E Team, the ‘Plan van Aanpak verbeteren gebruik Plug-In hybride auto’s’ (‘plan of action for improving the fuel consumption of plug-in hybrid cars’) was devised. To support this, TNO is monitoring real-world fuel consumption levels and the proportion of kilometres covered using electric power on the basis of data supplied by Travelcard Nederland BV and MTC.
Objective information for substantiating and monitoring policy
In Brussels, the Dutch government is lobbying for effective legislation at European level to make road vehicles cleaner and more fuel efficient. In order to get these cleaner and more fuel efficient vehicles on the road more quickly, the Netherlands is taking additional measures, such as tax incentives. The research being carried out by TNO is producing some important insights for the shaping and direction of European and Dutch policy. This includes efforts at bringing the tests more in line with actual practice, by making modifications to the testing procedure.
TNO is measuring and monitoring the emissions by road vehicles in various measuring programmes. Emission factors are derived from these emission measurements. Information about vehicle emissions, about the measurements of these carried out by TNO, and about emission factors, can be found using the links below.