MPG or MPD?

[Deja Q]

http://editorial.autos.msn.com/article.aspx?cp-documentid=450781&topart=luxury

One of the most fuel-efficient cars in America, the Toyota Prius will still only go about 15 miles on a dollar's worth of fuel.

[gateley]

1. Okay. If we had the technology to manufacture and then kill an electric car,

why aren't the car companies going that route?

I understand that the technology of lithium ion batteries is advancing.

One would think that the car companies could make a killing.

[Tesha]

13. Even with an electric car, the MPD numbers aren't that impressive.

Mr. Tesha and I sat down and worked the numbers for
a plug-in Hybrid (Prius + auxiliarry batteries) --
it's not much of a win just based on the economics
and it's unclear whether its a winner or a loser
based on pollution: modern cars are pretty clean
compared to central electric power stations, and
the overall system thermodynamic efficiency of the
oil refinery + car may be better than the overall
system thermodynamic efficiency of the power plant +
transmission lines + battery charging + battery
discharging + electric motor efficiency.

Note that if your electricity comes from a renewable
resource, the electric car is clearly better from an
environmental point of view.

Tesha

[madokie]

2. I go with the mpd myself

more relevent if you ask me. right now we're getting a little over 6 miles per dollar in our explorer

[nightrider767]

3. That good, 46 mpg. Great in my book. n/t

[FogerRox]

4. UM. lets see, 10 miles per dollar....@ $3 a gallon, thats 30mpg... no ?

HI way miles from my '96 Dodge Caravan.

[nightrider767]

6. OK,, I admit I skipped the math

But the Prius advertises itself as a 46 mpg/combined car.

We all ought to have one.

Anyways, another good reason to use mpg not dpg, as gases price fluctuations would lead to confusion.

[FogerRox]

14. another good reason to use mpg not dpg, as gases price fluctuations would lead to confusion.

Of course

[IDemo]

5. If the price of fuel was unchanging, that might be ok

The purpose of rating vehicles in distance traveled per unit of fuel is to measure their energy efficiency. Miles per dollar would be a continuously changing figure for any given vehicle and largely useless unless you're budgeting your weekly travel by fuel dollars.

[lumberjack_jeff]

7. MPD helps people make rational choices.

I live in a rural area, and knowing that it costs $4 to drive to town and back brings focus.

It also helps with the decision of where to buy gas. Let's say your tank is 10 gallons from being full. If your car goes 10mpd (30mpg@$3.00) then driving 5 miles out of your way to get fuel only makes sense if the fuel is more than $.10 cheaper per gallon.

[Solon]

8. Gas rarely varies, from station to station, by more than 5 cents...

and mostly less than that. Gas stations have no control over the pricing of their fuel, its administered by the suppliers, and there's no competition for it either.

[lumberjack_jeff]

10. I frequently see a 10 cent variation.

The stations in my town are always the same, (what a coincidence!) but 20 miles west and 30 miles east, fuel is 10 cents cheaper (bigger towns).

[Solon]

12. Yeah, but that's 20 or 30 miles away, too far away to make that big a difference...

I remember, working at Convenient Food Mart, which gets gasoline from Shell, our primary "competitor" is a Phillips 66 stations right across the street. Anyways, I worked afternoon shift, and one day I come in, and notice that our gas was a full 10 cents less than gas at the Phillips station. That night was fucking chaos, now, this was in 2001, so gas wasn't that expensive(yet), but I still had a LINE of cars going down the main road leading to my station, and we actually used up over half of our inventory for gas that night. Note, I was BY MYSELF, it was hell, and I quit a week later, it was stupid.

Oh, and the reason our gas was 10 cents less? The store manager, who worked mornings, forgot to change the price from the printout she got that morning. There's a special machine, behind the counter, that is mounted on the wall, that prints out the days gas fuel prices for us, and then the store manager is supposed to change the price in the signage and computer. I wasn't authorized to do that myself, I was just a "shift manager".

[EOTE]

9. Seems like a bit of a meaningless measurement to me.

Suggests that if the price of fuel drops, you can have a corresponding drop in fuel economy, and everything evens out. That's NOT the message we should be having now. Even if fuel was half the price it is now (like it was at the end of the Clinton administration), we should still be working as hard as possible to burn less of it. All this measurement is good for is to provide a more accurate measure of the financial impact of driving a particular vehicle at a particular moment in time. However, anyone who has completed 5th grade math should have a strong grasp of that these days anyway.

[SteelPenguin]

11. MPD? Seriously? Dumb

Since the ration of MPD to MPG varies sometimes on the day itself, or from station to station, you can't get any kind of relevant consistent number out of it. Plus inconsistencies between vehicles...

Just dumb imho.

The whole point of the article is that it makes it more obvious how much you're spending. If you need help with that then you're an idiot. Hell I have a Honda Civic that gets 35 MPG and I know that gas costs more now. I shudder to think how much that guy in the pickup is getting who is filling up next to me. If he says 10 MPG I know he's spending 3.5 times as much money as me. I don't need to add in some other fluctuating variable to complicate the situation with additional needless math.