Fuel economy standards cheaper, more beneficial than previously believed

September 6, 2017
Credit: CC0 Public Domain

The regulations that set fuel-economy and greenhouse-gas emission goals for cars and trucks have lower costs and higher benefits than previous analyses report, a new Carnegie Mellon University study shows.

The study is published in Environmental Science & Technology.

According to EPP Assistant Professor Kate Whitefoot who co-authored the report, the current standards are not nearly as difficult to hit—and can have even greater positive effects—once you account for the ability of automakers to make tradeoffs with other vehicle attributes. Under the current regulations, the National Highway and Traffic Safety Administration is required to set efficiency standards based on the available technology and economic practicability at the time. They meet this requirement by evaluating the costs and benefits of various efficiency technologies. They do this, however, by restricting the considered technologies to those that either maintain or improve other aspects of the vehicle's performance—particularly when it comes to acceleration time.

In her paper, "Compliance by Design: Influence of Acceleration Tradeoffs on CO2 Emissions and Costs of Fuel Economy and Greenhouse Gas Regulations," Whitefoot analyses the role that design tradeoffs, such as compromising acceleration, can play in cost-effectively bringing vehicles into compliance with regulations.

Credit: Carnegie Mellon University College of Engineering

"The costs of the regulations to consumers and automakers are lower than other policy analyses imply," Whitefoot says, "because they don't consider tradeoffs between and acceleration performance. Once we consider these design tradeoffs, our research finds that the regulatory are considerably lower, and fuel savings are much higher."

In other words, car manufacturers can redesign future models with slightly slower acceleration times and higher fuel economy for consumers. When manufacturers produce these vehicles for consumers who value lower prices over acceleration, it becomes much easier to meet emissions standards at much lower cost to the company. "This is a win-win for both consumers and automakers," Whitefoot says. "What's more, consumers that are willing to pay for better acceleration can still buy fast cars, because the regulations only set a goal for the average level of fuel economy and emissions instead of a mandate for every vehicle."

Additionally, Whitefoot's analysis has revealed that a slight decrease in acceleration can significantly reduce the overall emissions of the US fleet, as it will mitigate incentives to shift sales toward larger vehicles and light trucks relative to passenger cars.

The US government has been working with automakers for decades to make cars and trucks more fuel-efficient. Though the Corporate Average Fuel Economy (CAFE) standards have been in effect since 1975, they have recently entered more greatly into the public conversation, as the Trump Administration has called for review and re-write of these regulations, in hopes of making them less stringent. As such, the Environmental Protection Agency and the Department of Transportation have opened a public comment period, allowing the general public to weigh in on the proposed changes.

"To the extent that the federal agencies are setting the standards so that the public gets the biggest bang for their buck, the research supports that the standards should be more, not less stringent."

Explore further: Q&A: Change to fuel economy standards could impact consumers

More information: Kate S Whitefoot et al, Compliance by Design: Influence of Acceleration Tradeoffs on CO2 Emissions and Costs of Fuel Economy and Greenhouse Gas Regulations, Environmental Science & Technology (2017). DOI: 10.1021/acs.est.7b03743

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9 comments

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tblakely1357
1 / 5 (5) Sep 06, 2017
Distrust any study that has any political impact especially studies dealing with the environment, sexes and race. Science has always been affected by the political climate of the time. Sadly, it's much worse nowadays with numerous 'activist' scientists who are far more concerned with pushing their political agenda than doing real science. In fact many of them are in science just to push their agendas.
PTTG
5 / 5 (8) Sep 06, 2017
A> The benefits and citations of countless discoveries and developments, the fruits of which I can see every day with little-to-no effort.

B> An unsourced internet comment.

Yeah I think I'm gonna go with A here.
tblakely1357
1 / 5 (3) Sep 06, 2017
Reading comprehension is hard these days.
ThomasQuinn
5 / 5 (5) Sep 07, 2017
Distrust any study that has any political impact


This has to be among the absolute dumbest comments I have EVER read. So, we now have to distrust any study that, say, deals with self-driving cars, high-cost medical treatments, internet security, artificial intelligence, public safety, innovations in power generation, etc. All these and many more have significant political impact.

It is simple to rephrase tblakely1357's comment to mean the same thing stated more explicitly:

Distrust any study that has significant practical consequences


In tblakely1357s bizarre opinion, it seems that "real science" is only that science which has no practical effects. In the 18th and 19th century, the steam engine, leading to the Industrial Revolution, directly caused numerous serious political changes and political conflicts. Railways were a political project in practically all the world. Likewise, the chemical revolution of the late 19th century, electricity, etc.
antialias_physorg
5 / 5 (4) Sep 07, 2017
The funny thing is: in the EV market some companies are already figuring out that bigger electric motors (read:better acceleration) also means *better* efficiency because bigger motors have less of a thermal problem. And since electric motors don't have the wildly varying power/torque curves the way internal combustion engines do the size doesn't matter. Feed 20kW worth of power into a 200kW as opposed to a 20kW rated motor and you get 20kW output just the same.

Of course there's a limit (as bigger motors als mean more weight) but e.g. the new Nissan Leaf 2 is making use of this finding to extend its range over that of the predecessor while at the same time giving better performance.
Eikka
not rated yet Sep 07, 2017
Feed 20kW worth of power into a 200kW as opposed to a 20kW rated motor and you get 20kW output just the same.


That isn't strictly true, but for EVs the efficiency is nevertheless high enough that they don't really figure in this issue. In any case, hybrid vehicles overcome the "needlessly large engine" problem quite well. The tradeoff is in the cost of ownership.

And of course, the CAFE standards are pretty lax compared to their Euro counterpart. The CAFE standard for 2020 for small cars is 49 MPG and for regular sedans just 36 MPG. That's already a reality with modern engines - it's just a matter of consumer choice.

Meanwhile the CO2/km equivalent standard in the EU by 2020 is 58 MPG for all small cars and 37 MPG for vans. All measures in US gallons. That's not really doable with gasoline engines, without serious compromizes in vehicle size, safety and performance.
Eikka
not rated yet Sep 07, 2017
The reason why a bigger electric motor, say 200 kW vs 20 kW doesn't necessarily give the same power output during acceleration is that the larger motor has more rotating mass, and the moment of inertia acts as if you added more mass to the vehicle itself. During acceleration, part of your output power is consumed in charging up the rotational energy of all the spinning parts.

The moment of inertia scales linearily with rotor mass, and quadratically with rotor diameter. hence why it's a better idea to have a long thin motor around a driveshaft, than say adding motors to all the wheel hubs.

This is why in racing cars, one of the very first things you do to tune up an engine is to install a lighter flywheel.
Eikka
not rated yet Sep 07, 2017
In tblakely1357s bizarre opinion, it seems that "real science" is only that science which has no practical effects.


I think that's not a very fair representation of the argument.

I see it as "Any science which implies revolutionary practical consequences should be viewed with suspicion as to its political motives".

For example, nobody planned the industrial revolution. They were just looking to make better use of resources. If someone came up to say "Let's revolutionize the industry!", you'd be right to be wary as to how, why and for whose benefit?

You can't predict the future course of technology without also predicting future advances in technology, which is logically impossible as it is unkowable. If you knew, you'd already have it. That's also why standards and quotas like the CAFE are fundamentally misguided: they're demanding the unkowable and punishing you for failing to meet it - like the ever-increasing demands of the Soviet 5-year plans.
rrwillsj
5 / 5 (1) Sep 07, 2017
I think I understand tb1's argument that any apparent disagreement with his ideological position has to be wrong. No matter what empirical evidence is developed.

I have a more difficult time understanding E's arguments. You are correct that CAFE and other regulatory projections are all too often wishful thinking. But those are also still in constant evolution to try to take advantage of today's and tomorrows inventions. Perfection is desired. Do you believe it will ever be achieved?

Here on the West Coast for most of Los Angeles, it has been years since a serious smog alert. Except for the Port of LA and other West Coast ports have rising levels of pollutants due to poorly regulated maritime commerce.

A shiny example of regulatory success is the correlation between lead in gasoline and the murder rate. More lead spewed into the air, more brain damaged killers. Reduction of murders has followed the good-riddance of using such a poisonous metal in consumer products.

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