Measuring the emissions of powered two wheelers

Urban air quality is still a major problem. This is largely caused by road traffic. Mopeds and light mopeds contribute relatively little to the NO2 and particulate matter (PM10) concentrations in urban areas, even in places where there is a lot of moped traffic. They are, however, responsible for a significant percentage of the hydrocarbons (HC) and carbon monoxide (CO) emitted by traffic.

Mopeds vary widely in terms of emission level and fuel consumption. In general, 2-stroke mopeds are more polluting than 4-stroke mopeds (the terms ‘2-stroke’ and ‘4-stroke’ refer to the operation of the engine). The emissions of 2-stroke mopeds can also be more adversely affected if they are derestricted. Due to the types of speed limitation being used, the 25 km/h moped versions (low-speed mopeds) have higher emissions and a higher fuel consumption than 45 km/h mopeds. TNO has developed emission factors for various vehicle classes, road types and traffic situations. Moped emission factors are based on a limited data set. The contribution of mopeds to nuisance and air pollution at a given location is dependent on the type of mopeds being ridden at the location in question. TNO has investigated the composition of the moped fleet in the cities of Utrecht and Amsterdam. The results show that this moped fleet mainly consists of relatively new (less than seven years old) light mopeds. Mopeds and low-speed mopeds with 4-stroke engines currently make up around three quarters of the moped fleet. Those with 2-stroke engines are slowly but surely disappearing from the streets. Furthermore, it is noteworthy that a large percentage of low-speed mopeds are capable of speeds significantly in excess of the maximum factory speed of 25 km/h.

Emission legislation is in place to tackle emissions at source. This legislation is designed for new vehicles. Before a new type of vehicle is permitted on the road, a variety of type-approval tests are carried out, all of which must comply with the emission requirements. A range of measurements have shown that mopeds in real-world operation often fail to meet current European emission standards. The European Commission plans to introduce more stringent requirements and testing procedures for motorcycles in 2020, and has asked TNO to validate the new requirements and tests. Studies are also being carried out to identify procedures, such on-road emission testing, that could supplement current laboratory tests.

Read more

• TNO 2016 R10093 Brommers in de stedelijke leefomgeving - Status rapport
• TNO 2013 R10232 Emissions standard and tampered mopeds
• TNO 2014 R11088 Emission model for two-wheeled mopeds (not yet published)