What does it mean for a car to get 230 miles per gallon?

Written by adam


GM has created a bit of buzz around its claim that the Chevy Volt gets 230 miles to the gallon in city driving. From the internet a great chorus has replied: “This number doesn’t make any sense!” And it doesn’t. The trouble is, it’s not clear what better metric exists for measuring the efficiency of all-electric or plug-in hybrid cars.

GM isn’t the only company to make such claims. Tesla has long stated that its electric roadster gets 135 “MPG-equivalent.” Nissan has responded to GM’s claims by announcing that its all-electric Leaf, also slated for sale in 2010, gets the equivalent of 367 MPG.

*Warning: from here out, the post gets a lot math-ier than I originally intended. If you want the punchline, skip to the bottom.*

Where do these numbers come from? For Tesla, the calculation is straightforward, but that doesn’t make it any easier to interpret:

> the total energy used for a full charge of the Roadster’s battery is 62.3 kWh (assuming a 15 percent loss). That’s equivalent to 1.85 gallons of gas for the 244 miles that the Roadster can go on a full charge – 244 miles divided by 1.85 gallons gives us a little less than the equivalent of 135 MPG.

This method of calculating “MPG” has the benefit that it’s completely independent of the energy source. You could apply the same calculation to the space shuttle running on liquid oxygen or to a steam engine running on coal. The enormous drawback is that the number is meaningless to car buyers. No one really cares how many kilowatt-hours are needed to move cars around. Instead, people care how many dollars are needed to move cars around, and they might secondarily care how much carbon dioxide is created in the process.

Using some standard figures for the average cost of electricity, the average cost of gasoline, and the average CO2 emissions per kilowatt of electricity, I translated the Tesla electricity usage into miles per gallon based on cost equivalence and carbon equivalence with gasoline: 89 MPG and 57 MPG, respectively. These are good numbers — well, OK, they’re great numbers, particularly for a high-performance sports car — but they’re not as eye-popping as the original claim.

The GM figure is even harder to parse. GM claims to have tested the Volt using a “tentative” methodology developed by the EPA. Although the EPA is staying quiet on the matter, many have speculated that the company wouldn’t be bragging quite so loudly if it didn’t have some tacit support from the agency. According to the informed speculation at Edmund’s, GM’s test methodology was to drive 40 miles on an electric charge alone (0 gallons of gas), followed by an additional 11 miles using the internal combustion engine (0.22 gallons of gas). The total of 51 miles on 0.22 gallons of gas yields a mileage of 231 MPG.

Fine. The problem here is that the Volt operates in two dramatically different modes. In the all-electric, limited-range mode, the car uses no gasoline and so gets an effective gas mileage of infinity. Once the battery is drained, the internal combustion engine kicks in and the Volt gets a more conventional 50 miles per gallon. The blended mileage is exquisitely sensitive to the percentage of time spent in each mode. If GM had decided to test drive the Volt for 80 miles rather than 51, the result would have been a rating of about 100 MPG — still great, but a massive step down from the marketing claim. On the other hand, if GM had chosen to drive only 42 miles, the result might have been a fuel economy rating higher than 1,000 MPG.

A four-figure mileage number would have evoked howls of derision, and the Tesla example shows why these howls would be justified. Along the metrics that consumers care about — $/mile or CO2/mile — the inflated figure would be wildly misleading.

So what’s a better metric? Arguably, for all-electric vehicles, we should ditch MPG altogether. Companies can make all the goofy marketing claims they want, but I don’t see much reason for the EPA to get in on the act. Miles per kilowatt-hour will do nicely, along with charging time and miles per charge, to define a vehicle’s performance. Even better, though, would be kilowatt-hours per mile, which scale linearly with the vehicle’s efficiency.

Plug-ins like the Volt, on the other hand, are a tough case. Because they marry two different energy sources (and possibly two different drive trains), the only thing you can really say about their efficiency is, “It depends.” Some have suggested the cars should carry two numbers: the range in all-electric mode, and the average MPG when the combustion engine is running. Using multiple numbers is not terribly consumer-friendly, but then, neither is using a single number that doesn’t mean anything.

Finally, as Hank at ecogeek reminds us, whatever method we use to measure the performance of electrics and hybrid electrics, these are all very fuel-efficient cars.

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  1. bluemonkey

    What GM tells about Volt is hundred percent true.
    This car makes 5 miles per kW/hour (electric mode), and 50 mpg hybrid mode.
    1 gallon gasoline (hybrid mode) = 50 miles.
    36 kW/hour (electric mode) = 180 miles.
    T O T A L = 230 miles.
    The electric car is very easy to built, and very functional.
    In 1899, a Belgian built electric racing car called “La Jamais Contente” set a world record for land speed – 68 mph – designed by Camille J

  2. Mike

    This is the sort of thing that’s going to give plug-ins or E-REVs a bad name. The EPA needs to come up with a different standard for these vehicles, because they are so different from the conventional cars.
    I would like to see two things. One, the distance I can travel on all electric power (you can even have two different numbers – like city and highway). And two, I’d like to see the fuel economy after the battery is drained.
    If anybody goes in thinking they can drive 230 miles on one gallon of gas, they are going to be sorely disappointed. Hopefully, GM et. al. will get that point sooner rather than later.

  3. Adam Stein

    One thing I didn’t mention in the post is that the EPA probably is required by law to give the plug-ins an MPG rating. If so, Congress would need to amend the existing regulatory framework to change this.
    Another issue is that auto makers need to hit certain fleet-wide fuel efficiency metrics under CAFE, so there will be strong pressure to give plug-ins good ratings to reward manufacturers for selling them.
    So, basically, this issue could be harder to fix than it first appears.
    bluemonkey — the Volt can’t go 180 miles on an electric charge. It’s electric range is about 40 miles.

  4. Mike

    Good points. The EPA should talk to Congress (I’m assuming that’s the procedure) to amend the rules for plug-ins and evs. If Obama really wants millions of plug-ins on the road, we need to be able to deal with them in a rational manner.
    Better to deal with it now, than later.
    And even better, the marketers for GM, Toyota and so on need to get on board with the differences. I know that in talking with others who do not keep up to date as much as I do that there is some excitement about the Volt building. Until I ask them if they know the pricetag. The same is going to happen with these fuel efficiency numbers. If people feel like they’re being lied to their response is going to be very negative.
    As for CAFE, the companies should get the ‘credits’ for producing these vehicles. But again, it needs to be more rational.
    What happens when Toyota comes out with a plug-in Prius that gets a lower mpg number than the Volt, even though it’s more likely to be more fuel efficient in the long run? Just because it will run only 10 miles on electricity?

  5. bluemonkey

    The battery pack itself, rated at 16 kilowatts/hour, comprises more than 220 separate cells wired in series. That means the failure of any one cell disables the entire array, though some existing hybrid vehicles also have this flaw. The Volt pack is about six feet long and weighs a hefty 375 pounds.
    Voltage: 320

  6. Jesse

    Adam, your discussion of the MPG problems with the Volt is good (I too have been dissecting the cost in MPG calibrated for dollars and carbon). But I think you missed two big problems:
    1) The 230 miles per gallon is misleading, not just because it is so sensitive to the usage of the electric and gasoline modes, but because it ignores the energy used in electric mode. Which you and I both know is bogus.
    2) You ignored the biggest travesty here, which is the 367 MPG claimed by the Leaf. I broke those numbers down as well, and found that the Leaf was getting that number be including the 6.67x bonus that CAFE applies to non-petroleum vehicles as a bonus to a manufacturer’s fleet average.
    These electric vehicle manufacturer’s need to stop blowing smoke about their fuel efficiency, because it is going to come around on them big time.

  7. Rusty West

    Keep it simple:
    For PHEV’s give 3 numbers:
    1. Equivalent MPG in All Electric mode
    2. MPG in Gas mode
    3. Miles/charge in All Electric mode
    For EV’s give 2 numbers:
    1. Equivalent MPG
    2. Miles/charge

  8. Adam Stein

    Both good points. Honestly, this article was just getting much longer than I intended, so I punted on digging into the electricity side of the equation. And for the Leaf, I simply have no idea where their number comes from. If it’s true that they’re using a multiplier, well, that’s shameful. In my opinion, GM is basically being truthful with its 230 MPG claim. But using a 6.67 multiplier is just a flat-out lie. Are you sure, though, that that’s what Nissan is doing? I’ve read that they’re using a Department of Energy formula, but I don’t know the details.
    On a related note, I’m not sure how much the electricity side of the equation matters as a differentiating factor. From what I’ve seen, all electric cars perform fairly similarly in electric mode, and they’re so efficient compared to gasoline-powered cars that the differences are somewhat marginal from a consumer standpoint.

  9. Jesse

    Adam, I hesitated to link to my own blog since it can seem kind of cheesy, but you asked, so here it is:
    The short version: the DOE formula actually comes up with an MPG of about 55 based on a well-to-wheel efficiency of power plant to wheels, and then applies a 6.67 multiplier per the CAFE law for the special treatment of alternative fuel vehicles.

  10. BobboMax

    The cost and frequencies mentioned for battery pack replacement make it clear that amortized battery pack cost will be an important factor in the financial bottom line, which to me is life cycle cost per mile. Of course “your results may vary” depending on your driving habits.
    The lack of data on replacment cost and frequency make the calculation problematic at this point, but I think the Prius reliability results to date are somewhat reassuring.
    FWIW, I think the target demographic for Prii (proper Latin plural) is middle aged Unitarians- on a Sunday, my fellowship parking lot has more Prii/sq ft than any place but the factory parking lot, so in a year or two, I should be getting some good anecdotal data on life cycle costs.

  11. Crazy Marlow

    I think you nailed this.
    the big problem of measuring energy is that we use different units mpg and kw/hr.
    costs can vary on both.
    Storage in electricity and the integration of renewable power cells IE hydrogen could revolutionize electric cars storage problem
    a $15000 hydrogen cell starts to make a lot of sense.
    An interesting sideline here is carbon footprint and energy cost
    we could develop a new metric here “cost of emissions”
    Tax the higher systems and encourage the clean efficient systems.
    Rate all vehicles this way and lets see who has the big foot prints.
    Crazy Marlow out

  12. Rubin Diehl

    IMHO, the only HONEST way to put it would be:
    – Electric miles range: 40mi for the Volt;
    – Miles per kWh (real kWh from the outlet) on pure electric mode: about 3mi/kWh, if the Volt has a 16-17kWh pack;
    – Miles per gallon on hybrid mode: around 50mi/gallon, if the Volt performs similar to a Prius.
    Another fair and straight way to inform the consumer would be:
    – miles per gallon, driving 50% miles on gas, 50% on electricity;
    The total no. of electric miles on a single charge would also be informed, of course.

  13. gatcheson

    Don’t forget cost. While the CO2 is important and the government has to find a mpg equivalent, the measure that consumers really care about is how much it COSTS to drive. Prices vary, but I used 8.5 cents/kWh and $2.70 a gallon to break down a few of the cars mentioned here. My miata at 25mpg is $10.80/100 miles.
    Leaf – 2.04 $/100 mi
    Tesla – 2.20 $/100 mi
    Prius – 5.87 $/100 mi
    Volt – 6.30 $/100 mi
    (1st 100 mi from charge)
    Hummer – 19.29 $/100 mi
    For the Chevy volt I just used a straight-up 100 miles from charge, the next 100 would actually be less (5.40). Double the price of gas and really exciting things happen, because the Hummer becomes almost $40 while the Tesla is unchanged. But the Volt and Prius swap places at about 9 and 12. Go gas tax.

  14. Rene LeBlanc

    I agree with Mike’s logic on this, but another factor of interest is what sort of performance limitations occur when the battery is dead and the vehicle must depend upon a small gas engine to recharge the battery while it is being driven?
    Perhaps a realistic way to calculate gas mileage is to assume that most gasoline powered cars have a range of 300-400 miles per tank. We could base a mileage rating upon a standard 300 mile distance. This would reward vehicles that have a large battery capacity, and that may be a good idea.

  15. Adam Stein

    I agree that $/mile is important (see post above), but your numbers for the Volt seem off. Intuitively, the Volt should do better than the Prius, and the Volt’s first hundred miles should be considerably better than the second hundred miles, because the engine isn’t even running for the first 40. Your analysis suggests that electricity is more expensive than gasoline on a per-mile basis. In reality, it’s about half the cost, give or take.

  16. Adam Stein

    Unfortunately, there would be nothing fair or realistic about this measurement. Most people have commutes less than 20 miles. GM’s 230-MPG figure, questionable though it may be, is actually a lot more realistic than a test drive based on a 300-mile road trip.

  17. gatcheson

    Ah yes, I have the charge for the Volt wrong: I used 36k Wh for the full charge for 40 miles but it looks like it should be 16. That would change it to 4.60 $/100 miles.

  18. Adam Stein

    I think it’s actually 8 kWh, based on usable capacity. It’s a bit hard to tell from publicly available info.

  19. michael

    With repect to mpg I am still coming to grips with a direction comparison between electric and gas…the two are different and in some shade of light should be rated based purely upon their energy content.
    I understand the need to compare but that very comparison can make for cumbersome calculations…on the show room floor.
    Now, how each pollute might be a better comparison – comparing mining to refining and burning crude with coal or hydro generated electricity.

  20. jonak

    blue monkey
    pistin engines have a life of around 10-15 years on average, or around 150k miles
    The Prius battery pack also has an anticipated life of around 150k miles.
    Seems like your opinions are slanted…..Which part of Chrysler did you work for ?

  21. Apex Alex

    interesting. my UU fellowship in fairbanks, alaska, is also the one place in town with more Prii per sq/ft than anyplace else. one owner still has the original Gen I model (bought from another person who wanted a new Prius, got it bent and is not on his THIRD.) another couple is on their 2nd Gen II model.
    this, in interior alaska where winters are most definitely NOT battery friendly!

  22. Apex Alex

    as for battery longevity, the person with the Gen I model did have to replace a battery. but NOT the primary motive one. only the small 12v to run accessories. and he sidestepped the usual big dealer markups by just getting a motorcycle battery from sears.

  23. Tom Harrison

    Watts and CO2 together are a fair comparison, if meaningless to today’s car driver, whose only input is gasoline.
    Watts in the form of electricity to your house cost money and result in CO2. How much money and CO2 depends. I am an NStar Green customer — I pay a bit more for a Watt than my neighbors, but all of my electrical usage is made up for by generation from wind turbines. For me, a plug-in car is more expensive, but has almost no CO2 emissions.
    Of course this discussion will evolve/devolve to a question of the embedded energy of the car itself, which is, as with all cars, huge. And a little huger still when one considers the lifetime cost of batteries.
    But all of this misses the larger and longer-term point.
    In some future time, one could imagine that electricity is mainly a non-carbon energy form. Maybe not next year (although theoretically it is today, for me with NStar Green, or anyone buying a Terrapass House Offset). In some other future time, one could imagine that the cost to generate electricity falls significantly, A true dreamer could believe that fossil fuels become relatively more expensive because their CO2 externality has been figured in to their cost to the end user. And yet another future holds batteries that don’t completely suck.
    These futures will all come. Cars like the Prius made people think, “Gee, adding some electricity to the mix isn’t as stupid as I thought”, and cars like the Volt and Leaf may make people think “Electric cars are actually kind of cool, and you know, they’re actually practical, and gosh, they aren’t just golf carts after all.”
    We tend to think that the future brings us cool things. Indeed, its the present that reveals what cool things today will be practical and common in the future.
    The automotive industry, for all its failings has shown this truth over and over. I sure hope that GM’s future vision turns into a present that is practical.

  24. BobboMax

    “A true dreamer could believe that fossil fuels become relatively more expensive because their CO2 externality has been figured into their cost to the end user.”
    That’s a great line. As part of my Unitarian thing, I’ve been researching the “moral cost” of electricity, that is, the $/kWH if all the externalities are included- in the NW, all the salmon that never make it past our dams, the backyard views “spoiled” by by the sight of windmills, the fishing grounds impacted by wave energy harvesters, nasty chemicals from the solar cell factories, and oh yes, the mercury and CO2 emitted by our coal burning generation plants. Not a lot of luck so far, partly because people just don’t get the idea, partly because it definitely is rocket science, even for first order effects.
    BUT, if we had energy prices that included externalities, we’d have one number to use for our figure of merit for transportation costs.

  25. skierpage

    I thought http://www.epa.gov/fedrgstr/EPA-IMPACT/2000/June/Day-12/i14446.htm is the official word on EPA’s “Petroleum-Equivalent Fuel Economy Calculation” , and it’s far more complicated than your math. It almost makes sense until I get to “fuel content factor”.
    Bluemonkey, I don’t appreciate you hijacking this thread.

  26. Jesse

    Fuel content factor is not related to fuel efficiency, but rather fuel economy regulations, i.e. CAFE.
    If you are a car manufacturer, CAFE requires you have a certain fuel economy across all vehicles you make. The “fuel content factor” is a way of providing an incentive to manufacturers to make non-petroleum fueled cars. If you make a car that gets an equivalent 15 MPG, but it runs on electricity, it contributes to your CAFE number the same as a petroleum fueled car that gets 100 MPG. That DOES NOT mean, however, that it actually gets 100 MPG. That’s why the 300+ number being reported by Nissan for the Leaf is totally bogus.

  27. dlmchale

    Hello all, what is amazing and the most exciting part is we are having this discussion. Just a few years back a ‘spotter’ for the other side would ‘pine’ about how the additional dollars to purchase would not offset the conventional ‘ride’.
    EPA needs to establish the miles per kw so when the mini-e, the leaf, phoenix motor car, that soon to arrive south korean ‘ride’ and these exciting ‘rides’ we’ve talked about here, when they come to market; then we can see how far we can go on a full charge. This is were the real fun begins like the computer industry.
    Now we all understand why Exxon/Mobil is getting into the battery business.
    Final question can they get one to look like a ’57 Chevy or ’58 Cameo P.U. or then again a ’56 t-bird with a continental kit (for my wife):)?

  28. michael

    A fuel’s ENERGY content can be directly related to efficiency…diesel, from memory, has about 30% more energy per unit than gasoline.

  29. Tom Harrison

    Yep, internalizing all externalities would eventually include all social, environmental, and human costs (although those moral costs could be a trifle sticky). I was just talking about CO2 costs, but that’s only a narrow slice of what we’re not paying for now.
    When we account for them all in dollars, then we’ll know what our society values most.
    On second thought, maybe we’re better off with our heads in the sand :-).

  30. BobboMax

    I really think it’s possible to get a handle on at least a significant number of the first order externalities for electricity and the major fossil fuels (coal, oil, methane,) a SWAG level of accuracy, perhaps +/- 25% if I’m lucky. It wouldn’t do for writing legislation, for example, but you could say, “Well, if you’re spending $100/month of fossil fuels, you should consider spending an additional 32% on remediation projects. Let your conscience be your guide.” Kind of like when the Pope used to sell indulgences, so you could sin and still get into heaven, if you were rich enough.

  31. Chris R

    Jonak (earlier) had a good question–are you working for Chrysler or are you just someone with an axe to grind against Hybrids? My wife and I both drive Hybrids, hers a Civic, mine a Prius with a Hymotion supplemental battery pack.
    My tires have well over 25000 miles on them, snow, city, highway, summer… and don’t need replacing any faster than any other tires. The stock tires’ manual said to observe them “regularly” after 5 years, and replace them after 10 regardless of how they look. They’re warranted for 6 years… My wife’s tires have much less mileage on them, but have the same 5y/10y guidelines (specifying “annual” inspections) and are only warranted for 1 year or 12400 miles. No special tires, no extra expense, just go to Canadian Tire and buy ’em off the shelf.
    I’m not sure how fast batteries lose capacity, but I’ve not noticed any meaningful change in close to 2 years–my mileage stays at 63 MPG in the summer, 55 MPG in the winter. The Hyotion supplemental battery is fully discharged halfway through my day, and the stock battery, if it was discharging too quickly, would force the gas engine to kick in more frequently… If my batteries are losing capacity, it would reflect in my mileage. The stock battery is warranted for 8 years or 100000miles, the Hymotion one for 3 years, but it loses only 20% of its capacity after 7000 uses. Replacing the stock one is (according to an old LA Times article) $3000. A new Hymotion Battery is not priced (I asked the installer, but he said he’d never needed to do one, so didn’t know), but large mass-produced Lithium batteries cost ~$500 /kWh, so maybe it’ll cost $2500? My wife’s Civic battery is warranted for 8 years / 80000 miles, and will cost $2500-3000 to replace.
    The website listed for information on lithium batteries refers to the ones you buy at the grocery store (duracell, energizer, etc), not to the ultra high-tech ones in modern cars. Just last week 2 of our D size lithium rechargeables died for good after only 2 years. But our cars keep (silently) chugging along…

  32. Tom Harrison

    Chris —
    There’s a reason your Prius batteries last a long time: they were engineered to do so. The car will only discharge them to around 30% and charge them to around 70% — this means that they live in their “sweet spot” of performance, lifetime, and power … at some expense (60%, perhaps) of their complete ability. It’s a simple and obvious trade-off that Toyota made — everyone talked about how the batteries couldn’t possibly last. So they made them last, and put on a warranty to prove they meant it.
    I also concur with your point about replacement. If either or both of our Priuses last for 100,000 miles, I would have certainly spent more on replacing or repairing the normal wearing parts of a normal car thant the cost of a battery pack — people talk as though the car was 100% lithium or something.
    The battery isn’t really that much bigger than a standard lead-acid battery in a normal car … it’s just made of a different material. And while lithium has its costs as a metal, so does lead. And, by the way, cars are by far the most recycled product on the planet … and lithium, nickel, and lead all recycle easily and with minimal loss.
    Our first Prius is now 4 years old, and we’re still getting 50+ miles per gallon year round (a bit less in winter, a bit more in summer — just like all cars). Our second is three years old.
    Sorry to rant, but it makes me angry to see people talking as though the Prius or other good hybrids, like the Civic are some sort of Frankenstein experiment. The car works, and it gets far better mileage than any other car on the road for the last few years. And if the Volt, or the Leaf are successful (and I hope they are), it is on the shoulders of the Insight, Prius, Civic, and all the other hybrids that came after.
    Nothing makes me happier to see companies coming along and beating what is, in truth a very modest mileage of 50MPG. I don’t feel good, or smug when I drive my Prius — I try not to when better alternatives are feasible. But after 60,000 miles of driving two Priuses, we have used about 1,200 gallons less gas than an average car … in other words, 1/2 as many. It’s a trivial amount, to be sure, but a million here, a million there, it adds up, no?
    OK, I’m done now. 🙂

  33. michael

    As a car enthusiast I am quite intrigued by hybrids; true performance need not be how fast a car can go. But I am very concerned with the life of batteries. I have driven just over 200,000 miles on every car that I have owned and although replacement costs begin to ramp up after 150,000 miles, none of these have been for non-maintenance engine repairs.
    I do not know the cost of replacing the battery(s) in a Prius or Honda. That written, all else about these cars is conventional…replacing brakes, tires, CV joints, ball joints etc is no different.
    Most gasoline fired engines require timing belt replacement – this is very typical of Honda and toyota. Thankfully my current rig has a timing chain. and because hybrids use a conventional gas engine, spark plugs, air filters and perhaps individual coil packs for each cyclinder require perodic replacement. The oil still needs to be changed as well.
    So a hybrid has both a conventional motor and an electric(s). If the electric motor lasts until 100,000 miles, and costs $4,000.00??? to replace then Im not so sure the technology sniffs well at all. In my case, I’ll need another battery at 200,000 miles. Stacked on top of a battery replacement is the maintenance cost of the conventional motor siting next to the battery.
    On the other hand, fuel mileage and clean air benefits are perhaps trade offs we need to make since we all subsidisze the cost of dirty air and the cost of fuel – foreign fuel to be exact.

  34. bob fulford

    No matter how effecient one makes an automobile the problem…the true problem…remains: the automobile itself.
    When we change the goal from “a better way to move folk around in cars” to “a better way to move folk around” is when we will more likely solve the problem.
    And the problem WILL be solved. When urban areas became filled with mounds of horse apples,dying and decrepit horses and horse carcasses lying around for days the private auto caught on. (and that solution became another problem as solutions often do)

  35. Peter Chicago

    Soon cometh a technology with few or no faults.
    A very sad day for many of you.

  36. michael

    Actually, it’l be a great day…but trade-offs are part of life and a car is a giant trade-off, in any form.

  37. BobboMax

    (and that solution became another problem as solutions often do)
    Yes, one of my favorite mottos is “Every problem began as a solution to an earlier problem.”
    On the subject of cars as people movers, if you run the numbers, cars are surprisingly efficient people movers- an SUV w/ just a driver is on a par with a bus w/ two passengers, but if you compare a Prius w/ a driver & a couple of passengers to a half-full bus, the Prius does quite well, especially when you factor in convenience and the value of people’s time. (And by necessity, busses often run half-full, in the sense they start their run empty and at best arrive at the end point full. During commuter hours, they often make a nearly empty run back to the starting point.)
    None of which is to deny that we have an ecological problem produced by our need and insistence on mobility.

  38. Jacque

    Can’t this just be a simple equation? Charge up the battery to full, fill up the gas tank, and see how many miles it can go until the battery and tank are empty. Granted, this will only work for mixed-fuel vehicles, and for the electric-only vehicles, well, I don’t have an answer.

  39. Anonymous

    About the horses and horse manure clogging the cities? That’s what is called common knowledge….everyone knows that. I did not mean to tell you something you did not know, I meant just to draw a connection you may not have seen yourself.