European automakers have attacked proposed emissions standards that would place greater restrictions on cars, as well as large commercial vehicles like heavy-duty trucks and buses, as unrealistic.

It's not unusual for companies to oppose stricter regulations on their products, but in this case the auto industry's argument has won it an unlikely ally.

Both the ACEA lobbying group and the environmental group Transport & Environment oppose the new regulations for the same reason that carmakers do.

DON'T MISS: First-Ever Emissions Rules For Airplanes Proposed By U.N.

That's because the new emissions plan includes deep cuts for road vehicles, but completely ignores emissions from both ships and aircraft, reports WardsAuto.

The proposed rules were revealed in a formal policy paper published by the European Commission July 20.

They were drafted to help the EU meet a goal set in 2014 of reducing greenhouse-gas emissions 40 percent by 2030 compared to 1990 levels.

2017 Honda Civic Hatchback

2017 Honda Civic Hatchback

Major points include greater emissions cuts for cars and small vans, as well as the first-ever emissions reductions for large trucks and buses.

Transport & Environment approved of the proposed truck limits, but joined automakers in criticizing policymakers' exclusive focus on emissions from road vehicles.

It criticized the EU plan as "completely devoid of ambition" on reducing emissions from aviation and shipping.

ALSO SEE: Coming up next: emission standards for airplanes

For its part, the European Commission argues that, because road vehicles account for around 70 percent of transportation emissions, the majority of cuts should come from that sector. Airliners, by contrast, are only 2 percent.

The rules haven't been finalized, so there is still room for possible emissions cuts from ships and aircraft, a spokesperson told WardsAuto.

Because of their international nature, regulating emissions from the aviation and shipping industries has proven difficult.

Airbus A320

Airbus A320

Earlier this year, the International Civil Aviation Organization (ICAO)—the United Nations' aviation agency—published draft regulations for aircraft emissions.

If enacted, those standards would require a 4-percent reduction in carbon-dioxide emissions from 2015 levels for new aircraft beginning in 2028.

MORE: Pollution Perspective: One Giant Cargo Ship Emits As Much As 50 MILLION Cars (Apr 2009)

They would also set new limits for airplanes already in production that would be delivered after 2023, with emissions reductions of 0 to 11 percent, depending on a plane's size.

But environmental groups have criticized the proposal, arguing that the rules won't restrain expected growth in emissions from airlines due to aggressive growth plans for the number of planes in the skies.

Airbus A380

Airbus A380

While airlines today make up just 2 percent of global carbon emissions, many analysts believe their emissions could triple by the middle of the century if projected growth in air travel occurs.

Separately, the Obama Administration is pushing the EPA to draft U.S.-specific standards for airlines that are expected to be somewhat stricter than those proposed by the ICAO.

Draft rules could be completed by January, but they would have to be finalized and enacted by the next presidential administration.

It's worth noting that reducing emissions from aircraft and ships can have a small benefit to cars, as it reduces their overall carbon footprint by cutting emissions associated with transporting them from factories to dealerships.


Follow GreenCarReports on Facebook and Twitter