Vehicle emissions - which puts out the lesser emissions - a car or a motorcycle?

My understanding is that motorcycles actually emit more emissions than cars. (not sure if this is still true).

They also seem to produce more noise pollution than cars (per vehicle).

Comparative engine size, the motorcycle pollutes more. No AIR pump, no catalytic converter, no carbon canister, no computer controlled devices such as OBD I or II.

I would wonder why that metric is useful though? Wouldn’t the most useful metric be average emission per person/mile? It is my understanding that motorcycles are fantastic from that perspective (but I could be wrong).

Little to no pollution equipment on a motor cycle, compared to a car. so the bike pollutes way more.
Worse is gas powered lawn mowers.

@gorillapaws -good point – what would be a good metric?

@elbanditoroso “what would be a good metric?”

Average emission per person/mile? In other words, if you think of vehicles fundamentally as moving someone from A to B (ignoring cargo), then we would calculate the average amount of pollutants per mile in the vehicle, and then divide that by the average number of occupants.

It is my understanding that buses pollute quite a bit on a per engine basis, but if you divide by the average number of people, it’s a much more efficient means of transportation.

Newer Diesel engines have very rigorous pollution standards on them with DEF systems.
that reburn exhaust particulates, making them quite clean compared to years ago, just look at the exhaust stack on a newer semi instead of black the end is quite clean.

Large city buses are diesel electric.
Small engines have little to no pollution equipment installed on them so they are the greater polluters.

The EPA standards for motorcycles on a grams per km or grams per mile basis are about 3x higher for motorcycles than passenger cars. (There is not a direct comparison but that statement is close.)
Aftertreatment is easier to add on a passenger car than a motorcycle. And there are far fewer motorcycles on the roads so their net impact is smaller. – even though they are dirtier on a grams per mile basis. .

EPA Emission Standards for Passenger Vehciles
EPA Emission Standards for Highway Motorcycles

The old 2 stroke motocycles had to be the absolute pollution champs.

Yes. The two stroke engines were horrific. “A single two-stroke engine produces pollution equivalent to that of 30 to 50 four-stroke automobiles. ” Source

^ I still have my Kaw 500 triple. Every once in a while I take it out and scare myself.
The Japanese called it the “Widow Maker” for a reason.

But it’s hard to compare a 2 stroke cycle motorcycle engine with a auto since there are no 2 stroke cycle engines in cars, if there are any. The OP did say “comparable.” And a 2 stroke cycle engine uses a gas-oil mix, which a 4 stroke cycle engine doesn’t.

There were plenty of cars with 2 stroke motorcycle engines. In the 70s a friend of mine won a brand new Subaru with the same 2 stroke 350 cc engine found in the popular Suzuki bikes of the period. The “car” was a certain death trap for anything other than the mildest of accidents.