Motorcycle Emissions - Bikes Go Greener

Published on 21 December 2003 by Gill

By 2006,exhaust emissions from new motorcycles will be the same as for cars. This is the main objective of the new European legislation seeking to reduce motorcycle emissions over the next four years.

The objective of the new EU-legislation will be achieved in two steps. The first one reducing of 60%the Carbon monoxide (CO) and Hydrocarbons (HC) emissions of new four-stroke bikes produced from 1st April 2003.The second one, entering into force on 1st January 2006, will apply a further 50%reduction compared to the 2003 limits. 2-stroke engines will see their emissions output reduce by 30% for CO and 70%for HC. Motorcycles have a quite low level of oxides of nitrogen (NOx) and limits will remain the same for 2003 giving the time for the Industry to achieve more drastic NOx measures for 2006.

The technical requirements set for new bikes produced from 2006 can be achieved quite easily with current technologies, such as fuel injection systems and catalysers. To give an example, the 1000cc Suzuki V-Strom produced in 2002, equipped with a regulated catalyser, oxygen sensor and fuel injection, complies with 2003 emissions limits and is very close to the 2006 ones.

In parallel with the implementation of these new emissions requirements, a new dedicated test cycle for motorcycles will be introduced. The World Motorcycle Test Cycle (WMTC), as it is officially called, will have its own emission limits but these will be set in co relation with the ones presently set in the legislation, to ensure a similar environmental performance. The new test will for a period run in parallel with the present modified car test cycle, giving temporarily the manufacturers a choice between two type-approval procedures.

In use conformity, checks and durability requirements will also be introduced from 2006, to control the conformity of original emission output of vehicles under normal conditions of use, and to guarantee the environmental performance during the first 30.000 km travelled.

The European Union will at a later stage introduce requirements for the measurement of Carbon dioxide (CO2), motorcycles will be included in this strategy. Fiscal measures have been agreed to encourage the fitting of devices making older bikes “cleaner” and new ones pre-complying with the emission limits set for 2006. However, Member States can still include a “pollutant factor ”in their national road traffic taxes and penalise older vehicles should they chose to.

Motorcycles:Comparative Study of Urban Environmental Performance

The use of two-wheeled transport in areas of high traffic density is seen by many as an effective means to reduce congestion and so speed the traffic flow. Some also argue that motorcycles offer an environmental advantage when compared to the passenger car. This paper reviews the most recent data that the Department for Transport has collected from emission measurement programmes involving both modes of transport.

It is necessary to understand what is meant by environmental performance. Currently, due to the political focus on climate change, low CO2 emissions from transport are seen as a key environmental parameter. More traditionally however the effect of gaseous pollutants on air quality has been the key concern and, particularly in urban areas, this remains the case. This paper therefore considers both CO2 and gaseous pollutants.


In 1997 the European type-approval procedures for passenger cars was amended to include the measurement of CO2. There is now therefore a considerable database from which to derive the CO2 performance of the fleet. The European Union has also entered into a Voluntary Agreement with motor manufacturers that will see the average emission of CO2 from new vehicles in 2008 reduced by 25% as compared to the emission in 1995. At present the CO2 performance of motorcycles is not routinely measured although this will be a requirement from 2005 (the inclusion of motorcycles in a programme of CO2 reduction is also under consideration). Motorcycle CO2 emission data is therefore limited to that measured in recent programmes associated with the development of new type-approval standards, nonetheless some trends can be seen.

Figure 1. Comparative view of motorcycle and passenger car CO2 emissions.

As may be expected, CO2 emissions from motorcycles tend to increase with increased engine capacity – this is generally true also for passenger cars. However, smaller motorcycles that are generally representative of machines designed for urban/commuter use, tend to deliver CO2 emissions lower than the best is better than the average value from passenger cars.

Gaseous Pollutants

The gaseous pollutants for which regulation applies limit values, are carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOx) and, in the case of diesel vehicles, particulate matter (pm). The emission of these pollutants is determined by driving the vehicle on a dynamometer (rolling road) and collecting the gases emitted from the tailpipe. The dynamometer provides a resistance to vehicle movement that compares with a stylised driving pattern that includes both urban and extra-urban driving behaviour.

First consideration of the comparative performance between the two transport categories may be a simple comparison of the regulated limit values that apply. Whilst passenger car emissions have been regulated for many years, motorcycles only became subject to regulation in 1999. Figure 2 serves to illustrate the comparison between the individual legislative requirements for the emission of HC and NOx from petrol vehicles.

Figure 2. Regulated limit values for hydrocarbon and oxides of nitrogen emissions.

It can be seen that, even in 2006 when the most stringent of currently agreed requirements are applied, motorcycles trail behind passenger cars by at least one evolution of emission reduction standards.

It is argued that the driving behaviour of motorcycles is different to that of passenger cars and that therefore comparisons over a common drive cycle are not valid. A recent development in motorcycle emission legislation has seen the creation of a new test cycle that is based upon data collected from motorcycles in everyday use.

Although there are only limited data available, it is worth considering the relative performance of motorcycles when tested over different driving cycles and with different interpretations. Figure 3 shows average values for HC and NOx from motorcycles whose emissions were measured when driven over the current regulated (R.40), the passenger car (NEDC) and the urban/extra urban element of the new motorcycle test cycle (WMTC). In addition, the results from the WMTC cycles have been adjusted to reflect two different driving patterns, 50/50 and 30/70 refer to the percentage weighting given to parts 1 and 2 of the WMTC test cycle. The high-speed element of the WMTC has not been considered in this appraisal. The motorcycles were all current production models. The columns represent the average emission (grams per kilometre) of the sample (the y-axis scale should be multiplied by 10 for the HC value).

Figure 3. NOx and HC results over various test cycles.

Whilst the data set is too small to make absolute judgements, this finding does indicate the sensitivity of emissions measurement to the drive cycle employed.

As might be expected, NOx emission is at a minimum over the R.40 cycle and at a maximum over the NEDC. HC emissions are similarly affected by the drive cycle employed and are at a minimum when measured over the NEDC and a maximum over R.40.

Although there are only limited data available, it is worth considering the relative performance of the passenger cars and motorcycles when tested over driving cycles that are considered to be representative of real use for the respective types but set in the context of the legislated limit values.

Figure 4 shows separate NOx data sets for motorcycles and passenger cars whose emissions were measured when the vehicles were driven over these test cycles. The motorcycles were all current production models and the passenger cars were all of at least Euro III (2000) specification and include diesel-fuelled models. The data points represent the grams per kilometre of emission that was measured from each vehicle. The y-axis also includes an indication of the passenger car emission limits from Euro I (1992) through to Euro IV (2005). To aid understanding of the plots the average measured emission for motorcycles is shown by a horizontal line.

Figure 4. Comparative plot of NOx emissions from motorcycles and passenger cars.

The higher NOx values for passenger cars shown on the plot relate to emissions from diesel vehicles.

This indicates that motorcycle NOx emission compares favourably with that from petrol fuelled passenger cars, with a mean emission level in the order of the Euro II passenger car limit.

A similar comparison of HC emissions from the same vehicles is shown in Figure 5

Figure 5. Comparative plot of HC emissions from motorcycles and from passenger cars.

This indicates that HC emissions from motorcycles are broadly inline with Euro II values. They are however worse than those of passenger cars that achieve significantly lower values than even those required for Euro 4 in 2006. There is evidence from the test data that much of the HC emission is related to carburettor technology which is still reasonably common on motorcycles but redundant on passenger cars. In addition all petrol fuelled passenger cars will have been equipped with catalyst technology whereas few of the motorcycles were. It is expected that the legislative requirements for motorcycles from 2006 will cause this situation will change.

Discussion and Conclusions

The development of representative drive cycles for different transport categories provides an opportunity to better compare their environmental performance. Despite this progress there are only limited data available at this time and therefore care must be exercised with any conclusions drawn.

In so far as climate change is a consideration, motorcycles have a clear advantage over passenger cars. The maximum emissions of CO2 from motorcycles recorded in recent tests, fall below the average values recorded from the passenger car fleet. This is true for petrol engined passenger cars that dominate the UK fleet and also the diesel fleet that exists on the basis of its fuel economy. If one considers lower capacity motorcycles which dominate the urban/commuter sector, their CO2 emissions tend to be less than half those of the average passenger car.

When considering gaseous pollutants it is apparent that the nature of the test cycle used during emissions measurement can have a significant influence on the results obtained. For the purposes of comparison this paper has considered the emission of two pollutants (NOx and HC) measured over “real world” test cycles that have recently been developed for both passenger cars and for motorcycles. Comparison of these results has been put in context by reference to the emission limits set out in legislation for passenger cars.

Lower legislated limits for passenger cars would suggest that the environmental performance of passenger cars would be better than motorcycles. The available data suggests that this is the case, although the margin of difference is not as great as the difference in legislated limit values would suggest. Average emissions of NOx and HC from motorcycles is approximately one Euro standard behind that from petrol fuelled passenger cars. However, the NOx performance from motorcycles is generally better than that from diesel fuelled cars that are increasing in popularity because of their fuel efficiency.

Future emission standards have been agreed for motorcycles and these are almost certain to cause the use of carburettors (a major cause of high HC emission) to cease. It is also expected that catalyst technology will be far more widespread in the motorcycle fleet providing further improved emission control. In addition, the complexity of the test cycle over which future motorcycle emissions will be measured should reduce the possibility for disparity between regulated and “real world” emissions.

Extract from DfT paper relating to work on the motorcycle emissions global test cycle.

Last reviewed/updated 30/09/04