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Motorcycles Emit “Disproportionately High” Amounts of Air Pollutants

Emissions ratios from two-wheelers and cars in the Swiss fleet. A number >1 indicates more emissions from the two-wheelers. Click to enlarge.

Motorcycles collectively emit 16 times more hydrocarbons, three times more carbon monoxide and a “disproportionately high” amount of other air pollutants compared to passenger cars in the Swiss fleet, according to a Swiss study to be published in the Jan. 1 issue of the American Chemical Society’s journal Environmental Science & Technology.

The study, by Ana-Marija Vasic and Martin Weilenmann of the Swiss Federal Laboratories for Materials Testing and Research, found both two- and four-cycle motorcycle engines emitted significantly more of these pollutants than automobile engines.

The researchers measured exhaust emissions of CO, HC, NOx, and CO2 from eight two-wheelers and compared them to previous measurements from 17 gasoline-powered Euro-3 compliant passenger cars performed at EMPA with the aim of ascertaining their relevance.

Several comparisons show that the powered two-wheelers on the market in 2001 produced significantly higher emissions of all pollutants except CO2 than gasoline-powered passenger cars from the same sales period. Whether in a direct comparison of mean unit emissions (in g/km), mean yearly emissions (in kg/vehicle/year), or fleet emissions (in tons/year) [calculated for the Swiss vehicle fleet], the two-wheelers’ HC and CO emissions were all, and often significantly, higher. In addition, the NOx contribution of the motorcycle fleet is roughly one-fifth that of the car fleet and is thus not negligible.

Motorcycles aren’t a primary means of transport in most developed countries, the authors note. As a consequence, they say, the importance of [motorcycle] emissions has been underestimated in legislation, giving manufacturers little motivation to improve aftertreatment systems.

Even though the motorcycle fleet is small in comparison with the car fleet, and logs lower yearly mileage per vehicle, their contribution to traffic emissions has become disproportionately high.

Present-day aftertreatment technologies for motorcycles are not as efficient as those for cars. Until recently, for instance, US emission standards for highway motorcycles hadn’t been updated in 25 years.

That regulatory situation is about to change, but more attention is required, according to the authors.

Even if they account for a comparatively small number of vehicles, motorcycles’ impact on traffic emissions cannot be overlooked. Directive 2002/51/EC of the European Parliament and Council is a step in the right direction. With the introduction in 2006 of new emissions limits which are intended to correspond to Euro 3 gasoline cars, and with checking procedures for the correct operation of emission control systems, motorcycle emissions are expected to decrease.

However, the fact that more than half of the two wheelers [in the research] failed the statutory test is indicative of the need for periodical inspection and maintenance.

With regard to this study, the introduction of similar regulations as for passenger cars such as checking the durability of the aftertreatment system and periodic testing of exhaust gases should be considered. It would therefore be expedient to repeat this study two to three years after introduction of the new rules.




2-stroke engines should be banned worldwide. Period. Hopefully the increasing gasoline cost will make 4-strokes more attractive (even if more expensive initially).


The vast majority of motorcycle engines are 4 stroke. In fact, you'd be hard pressed to find a street legal, roading going 2 stroke. The last one I can think of is the Aprilla SR 50, and you couldn't ride it enough to make a difference anyway.

Jon Abbott

I primarily ride motorcycles for higher fuel efficiency, but did not know much about their emissions until now. I know motorcycles sold in California require special emission system modifications (like in cars there), but not so in the other 49 states... Glad to see that CO2 and NOx emissions are much lower for motorcycles, despite the other issues. Thanks for posting the article!



Actually their NOx emissions ARE very high.

From the article:

In addition, the NOx contribution of the motorcycle fleet is roughly one-fifth that of the car fleet and is thus not negligible.


I looked into motorcycles and found they dont get the good mpg you would imagine. Most do 50mpg. Many do less. So there are cars that get similar mpg to a bike, like an Insight, Prius or certain diesels. Mothercycles are (or can be) much cheaper, faster, more fun, easier to Park, but the mpg is not as amazing as you would imagine.


Even 4 cycle engined bikes are polluting like crazy and they dont get as good of milage as many expect.

Some bikes get worse gas milage then a full sized sedan.


A few years ago I was camping and talked to a couple who were touring on a Honda Goldwing trike with a tent trailer.  Cute rig, but the owner told me that he got something like 25 MPG (exact figure forgotten) punching into the winds we'd been seeing.  My car, much bigger, heavier and far safer, was getting better than that.  (But I didn't look as cool.)

Motorcyles are mostly about speed and style.  If you really want economy, you can get a Honda Insight or persuade someone to commercialize something like the Lean Machine.


I don't think anyone rides a goldwing to save gas. That thing weighs 1000 lb. It shouldn't even be considered a motorcycle.


Actually their NOx emissions ARE very high.

From the article:

In addition, the NOx contribution of the motorcycle fleet is roughly one-fifth that of the car fleet and is thus not negligible."

Actually no. That statistic was about the Swiss fleet of vehicles which has absolutely nothing to do with the situation in our country.

If we start requiring heavy emissions controls on motorcycles it will murder every small producer. I know some people on here want to pursue any reduction in pollution with fanatical zeal. It will just push more business into the hands of a few large corporations. The same thing happened to the US auto industry and look where that got us. A couple of giant lobbies that tell us we should all drive giant SUVs, burn lots of cheap gas and build more highways. Sometimes a fragmented the market is a good thing. I'm not saying motorcycles shouldn't have emissions controls on motorcycles. But the way we go about it in this country is Draconian and it only benefits the big players.


Goldwings weigh something like 900lbs and are about the biggest motorcycles you can get. They have a 1.8L six cylinder engine, HUUUGE for a motorcycle. It's the "S-class/760iL" of motorcycles. They have built in radios and for 2006 they even come with an airbag.

I owned a 2001 Yamaha YZF600R motorcycle for a couple years. It was a "race replica"/sportbike (aka crotchrocket) and had a 599cc (.599 liters/36.4 cubic inches) four stroke inline four cylinder engine. If I rode it at the same speeds (accelerating the same rate) as I do in my Ford Ranger it would EASILY get 60mpg...EASILY! Now if I rode it so I out accelerated every car in traffic 100% of the time (still not working the bike hard at all) I would get 45-50mpg NO problem what so ever. If I rode the bike like a bat out of hell and really got on it, I'd still get 40mpg...and I'd REALLY have to work at it to get to go below 40mpg.

Now if you flog a new 1000cc sportbike around a race track you'll probably see 30mpg, but riding at a sane pace on the street you'll get 35-45mpg usually. Not bad for something that can do the 1/4 mile in under 10 seconds (100% stock too) with a good rider who knows how to drag race.

If you ride casually (not fast, at a leisurely pace) on a Harley Sportster you probably see 45-60mpg. There are several full size motorcycles with single cylinders out there that are great for commuting and can get 60-80mpg.

Remember motorcycles are fun to ride and are usually viewed as toys. When people get on them they usually go a lot faster than they do in their cars, which hurts their mpg. They also have small tanks and it's harder to measure your mpg and get good consistant figures.

A new 600cc sportbike can do the 1/4 mile in under 11 seconds at the drag strip and give you 50mpg on your way there and back. A new corvette will do it in just over 12 seconds and might get 20mpg. You can buy a used literbike that'll do the 1/4 mile in the 10s and still give you 40mpg for as little as $5k, I doubt I'll ever see a car for $5k with that kind of performance (both acceleration and mpg).


Funny, my friend who owns a 550cc bike was getting about the same mileage out of it (35 MPG) as I got in my old VW.  $5/gallon fuel would have hurt him just as badly as me.

My new VW (bigger, much safer) hurt me on the last tank - it delivered 36 MPG instead of my usual 39+. ;-)

Doug Hawley

I am perplexed at the constant reference to the Honda Insight. Only 9 sold in Canada last YEAR and I think less than 100 in the USA. No Honda dealer will stock them as they don't expect to sell any.

The 2001-2006 Goldwing has emission control that qualifies to the Calif. 2008 standard. The Swiss study is only looking at the 2001 motorcycle fleet and does not reflect the more recent 2005-6 fleet upgraded with cataylists and careful fuel injection mapping. They are trying to beat a horse that has long left the barn.


The Insight gets better mileage than most motorcycles, carries two people in comfort and offers crash protection too.

Dave Zeller

I am curious about the overall demographics of the motorcycle fleet "studied" by The Swiss Federal Laboratories. The primary demographic to which I refer is the overall age of thse motorcycles.

Many people in both Europe and the United States ride very old motorcycles. Classic machines such as Harley-Davidson, BMW, Moto Guzzi, Ducati, Royal Enfield, and the orphan bikes from long extinct manufacturers tend to have very long product lives as many of them were designed with a capability to be recycled and rebuilt many times over,unlike modern transportation machines.

Many a rider in Europe bought a motorcycle with the intent of riding it many, many years, as the cost of living there seems to impede the frequent purchases of newer technology incorporating fuel injection, ignition-control computers, and other such things.

I myself ride a modern Ducati, which due to its modern technology can be rather peculiar in its need for expensive routine dealer maintenance. I can understand why many riders prefer a motorcycle that they can easily repair themselves, and thus take pride in. You cannot buy a modern motorcycle, with the exception of a Royal Enfield or Ural, that can be owner-maintained and repaired.

Lately, there has been much hot discussion among Europeans concerning the plague of anti-motorcycle regulations proposed by the E.U., which if inacted would essentially ban ANY and ALL motorcycles by 2020.

I shall speculate that if one was to look into this Swiss "study", one would probably see many of the E.U. prejudices incorporated in this report by a FEDERAL laboratory. In other words, a flawed "study".

Can anyone really expect a properly ordered, unopinionated study sponsored by any agency mandated by Government fiat?


Bikes can be very confusing in terms of fuel economy because of several factors. First, the primary factor is the engine size. The rough border is 500cc and bigger engines on sport/cruising bikes are for performance machines that are designed for fun and therefore have a poor efficiency - as bad as cars. However 500cc and smaller engines are designed for efficiency and other priorities (comfort) and achieve at least 50 mpg, can go as high as 100 mpg. Note that these are not fast machines, may have a limited range (city riding) and generally get much less attention than the more poweful super sports. So you can have 200cc - 300cc that can compete with Prius and Insight as well as 1100cc monsters that are worse than most cars and even some SUVs.

Second, riding style just like driving style affects efficiency. A leisurely ride on a 700cc cruiser can still achieve a decent mpg, say around 40 give or take. Unfortunatelly, many riders want to have fun and demand maximum power at all times which is obtained at a higher RPM. For super sports that would be around 10,000 RPM and more. I have met many riders who ride at such a high RPM all the time and simply don't care about efficiency. In those cases they will get a much lower MPG. The typical scenario is a 600cc super sport cursing at around 10,000 RPM which would yeidl around 25-30 MPG, comparable to a regular car.

In summary, since many/most MC owners ride for run they tend to have larger engines (600cc+) and use higher RPMs resulting in a very poor efficiency. These are simply choices people make.

The minority chooses smaller engines (less than 500cc) and don't pop wheelies ;) They get 50 MPG and more.

As for me, on my 600cc Kawi riding nicely (slow acceleration and gentle breaking, anticipate red lights, etc.) I get 5 l/100 mk, which is around 55 MPG I think.

In the end it comes down to people and their choices.


re: the motorcycles in the study.

The motorcycles were FAV 3/Euro 1, corresponding to the Euro 3 passenger cars.

1998 Yamaha YN50
1996 Piaggio Skipper
1997 Piaggio Vespa
1996 Yamaha Yp 250
1993 Honda Shadow
1993 Suzuki VS 800 GLP
1998 Honda VFR 800 FI
1999 BMW R1150GS

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