Enivronmental impact of replacing a car early

<div class='quotetop'>QUOTE(tballx @ Jul 22 2007, 04:39 PM) [snapback]483244[/snapback]</div>

This exact question has come up on PriusChat before, and I answered it to my own satisfaction along the lines you've already suggested. The key fact is this: For the typical straight-gas car, between 10 and 15% of life-cycle energy use is in creating and scrapping the car, and the remainder is in the fuel used (the 15% is from an Argonne National Labs study from about five yeas ago.)

If you are willing to make some assumptions -- basically, that the total number of miles driven by the US car fleet is going to be unaffected by your decision to sell your current car and buy a new one, and secondarily that "the car that gets scrapped" due to your decision to sell your current car gets US fleet average mileage (which, in the long run, sort of has to be true, in some sense) -- then the decision to buy a high MPG car (with in reason, as described below) reduces net total energy consumption of the US auto fleet.

In other words, if your miles in your new high MPG car ultimately displace an equal number of miles that would have been driven at the US fleet average MPG (after everybody trades cars and the worst one on the road gets scrapped), then the arithmetic is pretty simple: the more above average your new car's MPG is, the more often you can "buy new" yet still save energy in total for the US fleet. And the energy cost of building and scrapping a car is low enough, relative to the energy cost of the fuel, that you can buy one every couple of years or so and total energy consumption still comes out ahead.

So, take the data above as true and run some numbers. Suppose you are considering a 40 mpg straight-gas (non-hybrid) car. Suppose the car will last 150,000 miles at 15,000 miles per year (ten years). Suppose the energy for production+scrapping as as described above (15% of lifetime energy use). Then the net change in US fleet gas consumption is 375 gallons per year (15,000 miles at 40 mpg displacing 15,000 at 20 mpg), but you incur a one-time energy cost of about 600 gallons-of-gas-equivalent to build and eventually to scrap the car.

Bottom line: for that mileage, if you buy new no more often than every 2 years or so, you reduce net energy consumption.

It's a bit different because a hybrid uses somewhat more energy for construction, but not hugely more. Call it every 3 years for a Prius versus the US average.

At least that's how I see it this evening. The original thread was here:

http://priuschat.com/index.php?showtopic=2...amp;hl=pipeline

I though I was more quantitative in that prior thread but I was not. My best guess with a Prius is that buying a new one no more often than every 3 years reduces total energy consumption for auto transport. Not that under the assumptions here, this has nothing to do with the MPG of the car you are selling, only the MPG of your new car relative to the fleet average (or, of you want, relative to some lower target reflecting the fact that the oldest, nastiest cars are eventually junked as a result of a new car purchase.

 

I think this is an interesting question. What if you have an old (but thus far reliable) car. For instance, in my case a 96 Corolla with 100,000 miles on it. Who knows, but I could probably get another 50,000-100,000 miles off it. My guess is that IF i traded in that I would get more for it as a trade in (supposedly now 1750-2000 or so), then if I sold it. And I also guess that if it were a trade in they might scrap it. OTOH, I could sell it to some poor college student who would have some good reliable wheels for a few years, with moderate use.
So I am guessing that the more ecofriendly thing to do is sell it vs trade in.

I think this is moot for a newer car. Something with 30,000 miles on it is much more sellable and it wouldn't matter if you traded in or sold it.


Do you agree?

I am thinking now I am going to wait a year as I will have money in a year to buy outright.


--des

I think this is an interesting question. What if you have an old (but thus far reliable) car. For instance, in my case a 96 Corolla with 100,000 miles on it. Who knows, but I could probably get another 50,000-100,000 miles off it. My guess is that IF i traded in that I would get more for it as a trade in (supposedly now 1750-2000 or so), then if I sold it. And I also guess that if it were a trade in they might scrap it. OTOH, I could sell it to some poor college student who would have some good reliable wheels for a few years, with moderate use.
So I am guessing that the more ecofriendly thing to do is sell it vs trade in.

I think this is moot for a newer car. Something with 30,000 miles on it is much more sellable and it wouldn't matter if you traded in or sold it.


Do you agree?

I am thinking now I am going to wait a year as I will have money in a year to buy outright.


--des

 

I don't know, I had heard this once. That basically they didn't try to sell high mileage cars, it was just too hard. But my understanding was that most cars on a lot aren't really sold at the 'sticker price" and that the actual price they intend to pay for it could include a little wiggle room for a trade in that might sound generous over someone else's offer. Say someone offers me $1900 vs $1700, which is more the blue book. Wouldn't I think I was getting a good deal? But maybe they intended to give me that much off the sticker anyway. (See how much I trust them?? )

Otoh, this may not be right at all. Perhaps an old car like this is just auctioned to a "we finance anybody lot" or something.

BTW, I don't actually understand this whole issue. Since every year there are new drivers, then someone is going to be driving that car that you stopped driving. I suppose some degree of desire is put in. For instance I might not be thinking of another car if it weren't a hybrid, but someone is definitely thinking of their first car or a second or third car.


--des

<div class='quotetop'>QUOTE(tballx @ Jul 23 2007, 11:11 PM) [snapback]483932[/snapback]</div>

 

The supposed environmental impact of producing the Prius has been highly exagerated. For example, nickel mine in Canada has actually been cleaned up considerably from the extent of existing damage that peaked in the mid 70, before the Prius was ever on the drawing board. The use of this resource to product Prius batteries has been fairly recent, after the bulk of the serious environmental damage had been done through othe industries use of that resource.

Anyway, I think most cars you trade in will end up being used by someone, unless they are really shot. If the car is high mileage and doesn't meet the dealers late model, low mileage used car standards, it will go to the wholesale auction and end up at one of the cut rate car lots to provide basic transportaion for people who cannot afford to buy a late model used car.

 

If a car is really shot and no one wants it, then it isn't drivable. They scrap the metal and reuse it. Seats, etc. end up in lots and are picked up. I picked up glass and all sorts of goodies at these places.
Sometimes they get used in different way for instance theater props.


--des


<div class='quotetop'>QUOTE(NoMoShocks @ Jul 24 2007, 02:52 AM) [snapback]484029[/snapback]</div>

 

Another point that none of the proponents of this argument seem to consider:

Toyota is producing Prii as fast as they can. Their plants are running at full capacity. None of the dealers in my area seem to be able to get cars fast enough. So, if production is at capacity, and all of the cars are selling, the "carbon footprint" of making the vehicle exists regardless of your personal decision to buy a car. If you don't buy it, someone else will. Why not enjoy the operating benefits and reduced emmisions - the car will be made regardless.

 

<div class='quotetop'>QUOTE(Mad Hatter @ Jul 27 2007, 09:54 PM) [snapback]486551[/snapback]</div>

I think you have to be careful with this kind of arguement. yes the cars will be made regardless if you buy one or not, right now, but supply with try to match demand so if you don't buy one than that effects demand.

It is kind of like people who buy things that are socially or environmentally damaging (diamonds, fur coats etc) and say well the damage has already been done so I might as well buy the product. It's a completely rediculous way to jusify a purchase and misses the whole point.

Now buying the less damaging of two different products is obviously more responsible. So when buying coffee you know you are causing harm but you buy shade grown, fair trade certified instead of "Hills Brothers" sun loving coffee beans. Buying a Prius over a Tahoe is a similar venture.