Motorcycle NOx Emissions: Are old motorcycles really highly polluting?

by MotoGusto Editor

What is the truth about motorcycle NOx emissions? MAG’s Director of Campaigns and Political Engagement, Colin Brown, takes a look at the evidence for older motorcycles being highly polluting.

This article was originally published in Issue 82 of TheROAD magazine under the title “Show us the Evidence”.

For as long as MAG have been challenging the decision to charge pre-Euro3 motorcycles in London’s Ultra Low Emissions Zone, Mayor Khan and Transport for London have consistently claimed that many older bikes are more polluting than cars. MAG has consistently asked for the evidence base or data set to back this claim. This has been a simple request that has been consistently ignored. Finally, in an email dated 28th March 2019, TfL have finally pointed towards the evidence they are using.

National Atmospheric Emissions Inventory

So what is the database on which they base their claims? The answer is a spreadsheet that can be downloaded from the National Atmospheric Emissions Inventory website.

Naturally it behoves us to consider this information fully as MAG is not in the business of making false claims and assertions that are not evidence based.

Firstly, let us consider what this spreadsheet is.  The spreadsheet is entitled “NOx Emissions Factors: COPERT 5”.  This is essentially a spreadsheet giving emissions of NOx in grams per kilometre for various vehicle types and euro ratings at a given average speed.  Naturally this is the average for all vehicles of the same category.  It therefore gives, for example, the average grams per kilometre for Euro6 diesel passenger car of greater than 2.0 litre capacity, or for a Euro2 2 stroke motorcycle less than 150 cc at an average speed of 30 km/h. 

It is a very big and clever spreadsheet that allows you to input your preferred average speed.  TfL told us that the average speed they use for their analysis is 30 km/h.  This in itself is a little strange as we are pretty sure this is not the average speed of traffic in London, but let’s go with it regardless.


Now, if we are to accept the data in the spreadsheet we should understand where that data comes from.  The answer to that question is it comes from COPERT 5.  What is COPERT 5?

COPERT is an MS Windows software program aiming at the calculation of air pollutant emissions from road transport. The technical development of COPERT is financed by the European Environment Agency, in the framework of the activities of the European Topic Centre on Air and Climate Change.  In essence it is, therefore, a model based on some empirical data set. 

At time of writing we are not in possession of the actual empirical data used for the COPERT modelling, but (no doubt unlike TfL) we have asked the modelling software engineers for this data.  Why have we asked for the data?  Well that is because a model is not evidence.  Just as climate change models have repeatedly proven to be inaccurate, there is a possibility that this model is inaccurate.  After all we can see that a “degradation factor” is applied to calculate a drop in performance and increase in emissions as vehicles get older.  This would tend to suggest that there is room for error creeping in.  Has the validity of the model been confirmed by real world measurements?  At this point we don’t know.

The Evidence

Now, let’s say that we accept the model, and accept the 30km/h average speed position.  What does the spreadsheet actually tell us?

Well firstly let us remember that the standard set by TfL for NOx emissions for motorcycles is Euro 3 and specifically 0.15g/km.  When we interrogate the spreadsheet we might expect that all pre Euro 3 motorcycles show an average in excess of 0.15 g/km at 30km/h to align with TfL’s position.  However what actually find is that Pre Euro 1 <50cc mopeds, all 2 strokes, Euro 2 four strokes 250 – 750cc and all four strokes >750cc average below 0.15g/km.  What is more, for the “dirty 2 strokes” that we all thought would be an issue, the modelled emissions are less than half the 0.15g/km standard!

Interestingly we also find when looking at cars that all Euro 6c Diesel cars – the cleanest diesels on the road which will face no charges in the ULEZ, emit 0.21 g/km that is 140% of the permissible standard for motorcycles.


One final point to make here is that we are also confident that the figures take no account of the benefit that motorcycles display in congested traffic, the benefit that can be summed up in one word – filtering.  Again, being thorough evidence based thinkers, we have asked and await for confirmation from the COPERT software people.

So there we have it, within 15 minutes of receiving confirmation of the “evidence” backing TfL’s case for making the incessantly repeated claim that older motorcycles are highly polluting, we have been able to comprehensively demolish the logic.  If you have concerns about the particulates from 2 strokes, that is a whole new article, but safe to say TfL have repeatedly made the point that the ULEZ charges apply exclusively to NOx emissions hence arguments about forcing commuters to use the underground where particulate matter concentrations are up to 29 times higher than on surface streets are irrelevant.

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#motorcycleactiongroup #MAG #motorcyclenox #motorcycleemissions #motogusto

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