For some time now it has been known that emissions from mopeds, like other motor vehicles, can cause respiratory inflammation and hypersensitivity of the respiratory tract for example to allergens. Moped emissions can also damage the reproductive system and hereditary material (DNA). However, the severity and extent of the moped emission-related health effects are not clear for road users like cyclists. It is also not clear how these effects relate to negative health effects caused by other motorized vehicles. One reason for this is the lack of knowledge on the relationship between actual exposure and a whole range of possible health effects. This is the conclusion of an exploratory study carried out by the National Institute for Public Health and the Environment (RIVM) into the health effects of moped emissions. The study was commissioned by the Dutch Ministry of Infrastructure and the Environment (I&M). The reason for requesting this study stems from an investigation in 2008 by the Dutch Cyclists' Union into the exposure of road users to fine particles (PM2.5) and ultra fine particles (PM0.1) emitted by motor vehicles and which includes mopeds. Whether or not actual damage to health occurs through inhaling these emissions, was not clear from the present study. Factors that influence emissions from mopeds: The emissions from mopeds are influenced by various factors. For example, the type of engine, the mileage, engine tuning, maintenance, driving style, Euro class (which places demands on the emission) and technology. Measures for optimizing the combustion of moped engines result in less air pollution. This is especially true for the transition from two-stroke to four-stroke mopeds and the introduction of the fuel injection system, which requires less fuel to be used. The extent to which negative health effects are reduced by lower emissions of harmful substances from mopeds, however, could not be determined based on the present knowledge. Moped emissions per group of substances: Moped emissions contain quite a lot of hydrocarbons: almost one quarter (13-24 percent) of the total amount of hydrocarbon emissions from all road traffic comes from mopeds. The contribution to the carbon monoxide emission is 4-10 percent and the contribution to particulate matter (PM10) 1-4 percent. Mopeds emit per kilometre more grams of carbon monoxide, hydrocarbon and PM than cars and less carbon dioxide. The emission of nitrogen oxides per kilometre is similar to that of cars. However, the part played by mopeds in relation to the total traffic emission of group of substances is small.