When is it environmentally best to replace a vehicle?

I don't know that it really matters. After all, if you trade it in or sell it at 3 to 5 years old, it's not like it is just crushed or something, someone will buy it and drive it. The bigger issue is probably demand for new cars -- if they can't sell model X of a given new car, they quit producing more of them.

 

I usually get a new car every ten years. My Saturn was actually 9 when I sold it and bought the Prius.

The car you're selling is going to be used by someone. Would that person buy a worse, more polluting car if yours was not available? Would they, instead, buy a new car if yours was not available? If you keep your car another 5 years so it hits the 10 year mark.....how much more has will your burn and pollution will you produce? Yes, the person buying your car will do that...but you won't.

Each and every hybrid on the road makes things a little bit better. Start adding up the little bits and eventually you'll see a change.

 

I tend to drive it until the wheels fall off, but let's discuss trading it in after 3-5 years.

Who ever gets your old hybrid is getting something cleaner and more FE than at least 95% (more or less) of what's on the road. You are supporting hybrid technology and opening up the market for second-hand hybrids. At this point - no guilt. Maybe 15-20 years from now it would be a concern....

 

I was all set to send you to EDF's 'tailpipe tally' but they have stopped supporting that. See their alternatives at:

http://www.environmentaldefense.org/articl...?contentID=5578

Cars since 2000 can be sorted on CO2 or pollutant emissions at:

http://www.epa.gov/greenvehicle/

 

Yes, if what you're after is maintaining the environment then the #1 issue is avoiding your current vehicle being sent to the scrap heap. If that's your priority, you want to find someone who's a good driver, but poor. They'll drive that thing till the wheels fall off to save cash, and they probably won't total it along the way.

Not selling the poor-emissions car would actually cause more harm to the environment - since now, that buyer you would have chosen will buy something else of little difference while you keep driving a polluting car around even though you can afford better. Sell the polluting car and buy your Prius.

Choosing the right buyer is the key. Good luck.

 

So long as it's not being sold to a junk yard, i think you could sell it guilt-free. A vast majority of cars are driven 10+ years by one or more owners, with most of the others being totaled in an accident. I think you could be fairly confidant that, even if you aren't driving it, someone else is, somewhere.

 

<div class='quotetop'>QUOTE(David Beale @ Nov 17 2006, 12:07 PM) [snapback]350851[/snapback]</div>

I agree with every sentiment expressed so far. I think you can conceive of this in two parts.

First, by far the simplest way to think of this is as a pipeline -- full of people holding cars of varying qualities. Your new car comes in at the front, you sell your old one down the pipeline, ... chain reaction, everybody trades up who wants to ... and the nastiest car comes out the other end, to be junked.

But second, and this is where I sense your concern, aren't you kind of increasing the throuput of the pipeline by buying new cars at rapid intervals? Basically, the more stuff you put in up front, the more gets scrapped at the other end (if the pipeline is inelastic). Further, there's no guarantee the pipeline is inelastic -- perhaps the presence of numerous quality used cars encourages more net miles to be driven? So if everyone turns over cars rapidly, you might see both a decline in car age at time of scrappage (wasteful) and maybe greater miles drive due to more widespread access to higher quality cars.

So if you put 1 and 2 together, there has to be some tradeoff. If we all bought new cars every year, the age of the car fleet would decline, current emissions would decline, but we'd be pushing a lot of vehicles out the end of the pipeline, compared to a situation where we waited longer between car purchases. So at some point, the environmental costs of new manufacture and scrapping would outweigh the environmental benefits of lower current emissions. In theory. Tough to thinkwe'd be anywhere near that point, based on what I see on the road, but I can't claim to have studied it.

There are a lot of imponderables there, and in a quick Google search suggests there's an entire scholarly literature on this topic.

One piece of information is that, based on two good studies that I've read recently, at current car lifetimes, of the total life-cycle energy use of a typical car, perhaps 10-15% is in manufacture and scrappage, the other 85% is in the gas you burn. So, the energy cost of, say, scrapping a car one year earlier than you had to is maybe a percent or two of the entire energy cost of the vehicle. That's not the whole story but I think it suggests that reducing the emissions of the current fleet is more important than keeping a car on the road another year or two.

Second piece of information is that the cars still on the road are getting older, on average. That's clearly at leastly partly due to the switch to SUVs (light trucks). But at any rate, the high rate of new vehicle sales over the past decade has not resulted in shorter vehicle lifetimes. In part, I'm sure that's technology at work -- cars today are better than cars built 20 years ago. But in any case, the raw numbers (see site belw) show that, now, we're not pushing cars into the junkyard faster now than we were 10 years ago.

http://www.bts.gov/publications/transporta...gure_02_10.html

So, we aren't pushing cars thorugh the pipe faster, in fact, I guess the pipe is elastic, and we're both buying new cars and hold old cars longer. Doesn't look like you'll be encouraging anybody to scrap their car early.

Upshot: buy the darn Prius now.

 

<div class='quotetop'>QUOTE(chogan @ Nov 17 2006, 12:21 PM) [snapback]351043[/snapback]</div>

I just wanted to say that this is a really great post.

 

I don't know about the environmental angle but If you keep the RX-7 and get a Prius you can have two revolutionary vehicles in one garage

And yes I do realize that Wankel engines have fairly poor emission standards but it was/is a fairly ingenious way of re-thinking Automobile-tech.