Both the U.S. and Europe have implemented tighter emissions or fuel-economy standards for gasoline-powered vehicles, but Europe's legion of diesel cars and trucks may get even closer scrutiny.
As concerns over urban air quality grow, European analysts see diesel-exhaust emissions as the next major target of regulation.
A recent Just-Auto blog post claims further diesel crackdowns are only a matter of time.
Stricter Euro 6 emissions standards--which affect new models launched in the U.K. after September 1, 2014, and all new vehicles sold beginning September 1, 2015--have triggered the launch of cleaner new models.
Those standards are largely equivalent to the "Tier 2, Bin 5" standards in place for cars sold in the U.S. since 2008.
However, it will take time for new, cleaner diesel cars and trucks to replace the older, more-polluting vehicles.
Concern over diesel exhaust's cumulative environmental and health impacts is expected to grow in the meantime--in turn encouraging tighter regulation yet.
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Earlier this year, the World Health Organization (WHO) doubled its estimate of the number of people who die each year from exposure to air pollution.
This came after it re-evaluated the effects of pollutants such as nitrogen oxides and particulate matter.
In addition, the European Commission has proposed banning internal-combustion cars from city centers by 2050--and ensuring that zero-emission vehicles account for half of the total number of cars on European roads by 2030.
The changes will affect not only individual drivers, but fleet operators as well.
Analysts expect operators of diesel commercial vehicles to integrate more hybrid or electric vehicles into their fleets, or use telemetry to improve the efficiency of existing vehicles by restricting speed and planning more efficient routes.
Meanwhile, U.S. regulators are starting to look at a further diesel-emissions crackdown as well.
The U.S. may further tighten its Tier 2, Bin 5 exhaust emission standards in coming years--meaning that diesels sold in the U.S. could face the same challenges foreseen for Europe.