I've heard a lot of back and forth on this issue, but when purchasing our next vehicle which is actually the better way to go?

For us, we cannot go fully electric at this point due to drive times, and there is no good public transit close to our house.

This questions whether it is environmentally friendly to purchase a new hybrid, but doesn't really address the choice between types of used vehicles: How to determine whether hybrid cars are really better for the environment?

  • If someone would create a biodiesel tag and add it to my post, that would be cool. – Noel Feb 8 '13 at 15:57
  • With rare exception, I believe any used vehicle will be more sustainable than any new vehicle. But I haven't seen any studies to directly address this. – Flimzy Feb 8 '13 at 18:10
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    I think you've got a stranded half-sentence at the end of your first paragraph. – EnergyNumbers Feb 8 '13 at 20:07
  • Edited my post. I did not mean to say I was looking at a new hybrid. – Noel Feb 8 '13 at 21:38
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    I find it difficult to see how Flimzy's answer can be good enough to be accepted, when it provides opinions rather than referenced facts. At least EnergyNumbers' provided some links to support his/her assertions! – Mark Booth Feb 9 '13 at 21:01

TLDR; In my estimation, a new car never makes sense, from an environmental standpoint. And a hybrid never makes sense--it offers the worst of both worlds (all the pollution, manufacturing, and disposal footprint of internal combustion and electric).

All things considered, the fuel consumption of any vehicle is minor compared to the manufacturing, disposal, and maintenance footprints.

A used vehicle has the lowest manufacturing footprint, sometimes at the cost of greater maintenance footprint.

I have read (disputed) reports that the environmental footprint of a Prius is the same as that of a Hummer after 100,000 miles. True or not, it helps one think about putting fuel consumption into perspective of the larger picture.

Full disclosure: I have owned 6 diesel vehicles. I currently own an '86 TurboDiesel Jetta, and an '03 TDI Jetta. I have never owned a hybrid.

Without any specifics (because I don't know them):

A hybrid vehicle reduces emissions (although in the U.S., the most efficient hybrid is barely more efficient than the most efficient diesel vehicles, in Europe, there are even more efficient diesel vehicles). It increases manufacturing and disposal footprint.

Environmental factors which are roughly the same for both a used biodiesel and new hybrid vehicle:

  • Engine coolant
  • Motor oil
  • Repairs for: Suspension, engine, windshield, etc
  • Disposal footprint for any vehicle

Factors which are greater for a new hybrid:

  • Manufacturing footprint of a new vehicle
  • Additional manufacturing footprint for batteries, electric motor, etc
  • Additional disposal footprint for batteries

Factors which are greater for a used biodiesel vehicle:

  • (Possibly*) more fuel consumption, greater emissions
  • Possibly greater fuel manufacturing cost
  • Greater repair costs/footprint (compared to any new vehicle)

*My '03 TDI Jetta gets better fuel economy than all but the newest and smallest hybrids (and it's a lot more fun to drive). All biodiesel is not created equal. If you have a source of biodiesel recycled from used oil, the fuel refinement cost is practically nothing. If you are buying commercial biodiesel in the U.S., it is almost certainly made from soym and onventional soy farming is not sustainable. Although, the most recent numbers from the USDA suggest that soy biodiesel is more efficient than before (thanks @Nate). Although the USDA has a clear bias (an interest in promoting aggriculture), I have no specific reason to think their numbers are wrong.

My suggestion, in order of least environmental impact (assuming you are using the most fuel-efficient vehicle in each class, that will suit your needs):

  • A bicycle
  • A used all-electric vehicle**
  • A used diesel vehicle, with recycled biodiesel or straight veg oil (SVO/WVO)
  • A used diesel vehicle, with standard diesel or soy biodiesel
  • A used gasoline vehicle
  • A new all-electric vehicle**
  • A new diesel vehicle
  • A new gasoline vehicle
  • A used hybrid***
  • A new hybrid

**I don't actually know if an all-electric vehicle is better than internal combustion, but I suspect it is, because it reduces the mass of the vehicle, and many peripheral fluids (engine coolant, motor oil, etc).

***It's hard to rank hybrids accurately. Some biased sources claim they are devilspawn. Other sources, biased in the other direction, claim they're heaven-sent. The truth is probably somewhere in the middle. So take this absolute raking with a grain of salt.

Also note that even without biodiesel, a diesel vehicle is more sustainable than a gasoline vehicle. All other things equal, diesel gets roughly 33% better fuel economy than gasoline per fuel volume. Diesel refining is also, arguably, less harmful to the environment than gasoline. And lastly, a diesel engine is mechanically simpler than a gasoline engine, and thus will last longer (500k miles is common).

I suggest looking for a good quality used diesel vehicle. A 2000-2003 Jetta TDI is the ideal right now, easily over 50mpg highway. But even the newer Jettas still get excellent fuel economy, and the older ones can, too. My '86 gets about 40mpg. My '03 about 52mpg.

  • This depends on the batteries used. To get an apples to apples comparison you will need 3 batteries for the life of the vehicle to compare to the average life of an ICE. Some of the batteries in use are pretty horrible in terms of sustainability. – user141 Feb 8 '13 at 19:11
  • @Chad: You're talking about all-electric I take it? It's an issue I haven't investigated much, as I haven't been in the market for a new vehicle for the last several years, and last time I was, an all-electric wasn't really an option. – Flimzy Feb 8 '13 at 19:12
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    A goat drawn cart is the way to go. The ultimate in sustainablity :) – user141 Feb 8 '13 at 19:19
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    @Noel: If you can find a used hybrid that gets better fuel economy than a used diesel, the hybrid may win. But you can probably find a more fuel-efficient diesel than hybrid, which will make the diesel the clear winner (and more fun to drive, to boot!), – Flimzy Feb 8 '13 at 21:40
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    Some nice information on biodiesel (I drove a TDI for 5 years on bio). But, way too much unsubstantiated guessing to be a good SE answer. Unfortunately, biking around isn't really a good environmental solution either, unless you're in a dense, high-traffic city. Here, the human body becomes the engine, and it's also inefficient. You have to fuel it with food (and it's hard to do so without using energy-rich meat). A unit of food energy requires many multiples of that in inputs. And, bikes on roads without bike lines slow down the cars around them, making the cars less efficient. – Nate Apr 22 '13 at 7:20

Fuel consumption is typically 70-90% of a vehicle's lifecycle energy consumption and greenhouse gas (GHG) emissions, so there are lots of circumstances where upgrading to a significantly more energy-efficient vehicle makes a lot of sense. See, for details TRL VR6 and The UK Automotive Sector: Toward Sustainability.

If the vehicle being replaced gets a very large proportion of its materials recycled, then that helps even more.

It's worth noticing that despite all the FUD on the internet, it is pretty clear that when the science is done, hybrids are better than fossil-fueled internal-combustion engines.

But that doesn't make hybrids a sustainable option. If you're putting fossil-fuel in, they're not.

There are other, more sustainable options, and these will depend on your real trip patterns. For many households, an electric-vehicle for the vast majority of daily travel that's less than 120km, and borrowing / hiring / sharing a different vehicle for the occasional longer trip, will do.

The trade-off will depend a lot on your particular circumstances: if you've got an older biodiesel vehicle, it will depend on the lifecycle emissions of your biodiesel supply, and that will vary hugely around the world. If you get a hybrid, will it be biodiesel / electric hybrid, or something else? If biodiesel-electric, then it will almost certainly be better than an older biodiesel vehicle. If fossil-fuel electric, it could be worse, if your current biodiesel supply is pretty clean. Note that in that latter case, there will be trade-offs between local and global pollutants.

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    Energy consumption is far from the only factor when considering environmental impact or sustainability. – Flimzy Feb 8 '13 at 20:02
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    I've included GHG emissions (first paragraph) and materials recycling (second paragraph) too – EnergyNumbers Feb 8 '13 at 20:04
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    When a hybrid gets substantially better fuel economy than a straight IC vehicle, the additional costs may, possibly (I'm still doubtful) be overcome. But when a hybrid drivetrain provides little or no improvement, I think it becomes pretty obvious that adding toxic batteries to the mix does not gain anything. -- Unless your claim is that manufacturing or maintenance of diesel engines sufficiently more damaging than the batteries. But none of your sources seem to make this claim – Flimzy Feb 8 '13 at 20:32
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    @Flimzy, you don't seem to understand how a hybrid works. First, when a hybrid allows an electric motor to drive the car, it is using a fundamentally more efficient drivetrain. Electric motors are categorically more efficient than ICEs, and their transmissions. Secondly, the bigger gains from current hybrids come from the fact that some of the kinetic energy you create, by burning gasoline, can be recovered via regenerative braking. A car without regenerative brakes must waste all its kinetic energy as it slows down (as brake heat and noise). – Nate Apr 22 '13 at 21:38
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    @Flimzy, by the way, I'm not disagreeing with your conclusion that a used diesel running biodiesel is better than a hybrid using gasoline. I think bio is better. I just didn't agree with the implicit statement that a bio-fueled diesel car gets about the same (effective) fuel economy. The reason bio's better is that even though it spews CO2, the CO2 it produces was mostly already in the air, which is not the case for a gasonline hybrid. As I mentioned elsewhere, I ran some rough numbers here – Nate May 1 '13 at 2:09

I have driven a hybrid since 2000 and noted that I get 39.6 miles per gallon. This is primarily due to the fact that I do mostly freeway driving. I do get much better gas mileage when using city streets. This is because at lower speeds the hybrids will use the battery for power in place of gas. So when looking at a car you may want to take into account your driving habits.

  • Welcome to sustainability.SE! Note that unless it's a plug-in (to recharge the batteries) hybrid, the batteries are charged up by burning fuel in the engine, so when you're running the car just off the battery you're actually using charge that will need to be replaced later by burning fuel. – Highly Irregular Mar 17 '13 at 7:00
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    @HighlyIrregular, don't you get charge from the brakes, also? I thought that was one of the reasons why in-town driving yields better mileage. – Noel Mar 18 '13 at 15:54
  • @Noel, yes, but energy recovery from braking is only a fraction of what is lost to power the car. Much of the energy powering a car is lost to friction from the tyres and air resistance (which increases at higher speed, which would explain why town driving is more efficient). fueleconomy.gov/feg/atv.shtml – Highly Irregular Mar 18 '13 at 21:26
  • @HighlyIrregular, if by "a fraction", you mean something less than 1.0, then of course you're right. But, it's not a small fraction. Regenerative braking is the reason that hybrids get better fuel economy (about 25-30%) than the same model without the hybrid package. All cars lose energy from tires and wind drag, not just hybrids. Hybrids are more efficient because at low speeds (city driving), that's when you're using the brakes, and regenerating (recovering) energy. At 60 mph, you're not using the brakes much, and thus, you get no fuel economy boost vs. a non-hybrid. – Nate Apr 22 '13 at 7:31
  • @Nate, that's a fair point about fractions! Here's some real data claiming about 80kWh was saved over a period where 240kWh was used. It's not clear whether the 80kWh saved was included in the 240kWh as additional power consumed or not though. Looks like you are correct that it's significant. – Highly Irregular Apr 22 '13 at 9:17

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