Enlarge / Cars congest Intersate 10 in Los Angeles late October 2006. That year, the state sued several US and Japanese automakers for their alleged contribution to global warming. (credit: GABRIEL BOUYS/AFP via Getty Images)

On Tuesday, five automakers signed agreements with California's Air Resources Board to implement cleaner emissions standards over the next few years. BMW , Ford , Honda , Volkswagen Group , and Volvo will reduce vehicle emissions between model years 2021 and 2026.

Unlike Europe's rules, which fine automakers if they exceed a blanket fleet average for the amount of CO ₂ emitted per km, CARB has different targets for cars and light trucks based on their relative footprint. But each of the five OEMs has agreed to cut the amount of CO ₂ its vehicles produce per mile by about 17 percent by MY2026. The new agreement is broadly similar to one announced last year , although with a revised timeline that now runs through 2026.

Specifically, CO ₂ emissions from small cars would drop from 157g/mile in 2021 to 130g/mile in 2026, large cars from 215g/mile to 178g/mile, small light trucks from 195g/mile to 162g/mile, and large light trucks from 335g/mile to 278g/mile, with a formula to adjust vehicles that fall in between the small and large footprint areas. For context, the EU's new fleet-wide average, which came into effect in 2020, heavily fines any automaker whose fleet average exceeds 152g/mile (95g/km).

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  In 1980, Volkswagen built the ARVW concept car, the most aerodynamic vehicle it has ever created. It achieved a drag coefficient (Cd) of just 0.15. By contrast, most road cars have a Cd of between 0.3-0.4. [credit: Volkswagen ]

With no car launches to work on thanks to COVID-19, some automakers' press offices are filling the gap by digging into the archives to share interesting stuff with the rest of us. On Thursday, Volkswagen North America reached out to tell us about the company's most aerodynamic car ever. It was called the Aerodynamic Research Volkswagen, and it was built in 1980 as a demonstration of how to make a vehicle as slippery as possible, with a drag coefficient (Cd) of just 0.15. Powered by a 177hp (132kW) 2.4L inline-six cylinder engine, the ARVW reached a speed of 225mph (362km/h) at the Nardo test track in southern Italy. But the ARVW isn't the lowest-drag vehicle ever built, just the lowest-drag VW. So what is the most aerodynamic car of all time?

Production cars

When Tesla revealed its Model 3 sedan a few years ago, it was justifiably proud of the car's Cd of 0.23, which bettered the Models S and X by 0.01. Tesla didn't optimize the Model 3's aerodynamics just for bragging rights. The lower a car's drag, the further it can go per unit of energy because it doesn't have to work as hard to push its way through the air. However, a Model 3 is only this slippery through the air when the car's 18-inch wheels are fitted with the aero wheel covers, something Car and Driver put to the test late last year . (If you're a Model 3 owner and into hypermiling, you can cut your car's drag—and thereby boost its range—even further by fitting aftermarket front- and rear spoilers .)

But the Model 3 isn't the lowest-drag car to have gone into production. Porsche's Taycan battery EV bested Tesla's best when it went on sale last year. Both the Taycan Turbo and Taycan 4S manage a Cd of 0.22, although again, only with the most aerodynamic wheels fitted. The Taycan Turbo S uses a different design and in the wind tunnel, that adds 0.03 to the Cd.