Transportation

The transportation sector is a major contributor to our environmental problems; it represents 30-40% of our energy consumption. How can we reduce the environmental impact of our transportation needs in a way that makes cost/benefit sense?

Mass Transit

Begin by considering how to integrate mass-transit into your life. If you live on a farm in the mid-west and never go to the big city, skip to the next section; mass transit is not an option for you, at least not for local transportation. But if you live in Boston, New York, Chicago, Washington, DC, etc., read on.

To understand why mass-transit plays an important role in reducing the environmental impact of the transporation sector, we need to apply our cost/benefit methodology. What's the environmental cost of transportation? Fuel consumed and pollution exhausted into the atmosphere. What's the benefit? People moved. So the proper cost/benefit measure or metric is miles per gallon per passenger (miles/gallon/passenger). (Simple algebra tells us we can also call this passenger-miles/gallon.) Now please see Figure 1. The figure provides graphs of passenger-miles/gallon of fuel vs. number of passengers for 7 modes of transport:

• a 30 mpg Toyota Camry passenger car capable of carrying 5 people,
• a 50 mpg Toyota Prius Hybrid passenger car capable of carrying 5 people,
• a 16-19 mpg Toyota 4Runner SUV capable of carrying 5 people,
• a .833 mile/gallon train capable of carrying 1000 people,
• a 9 mpg bus capable of carrying 50 people,
• a .353 mpg Boeing 767, capable of carrying 213 people⁹,
• and a 2.55 mpg Cessna CJ2, capable of carrying 6 people¹⁰.

Note that this figure gives us the efficiencies of these modes of transportation assuming the best-case scenario - that each vehicle is loaded to capacity. In Figure 2, I make some assumptions that I consider reasonable about average occupancy of the vehicles, showing the efficiencies under those conditions. The estimates are: 1.5 passenger average occupancy for car, hybrid car and SUV, 20 for buses, 200 for trains, 100 for the airliner, and 3 for the business jet. I include this graph for your information, but will not use it in the following discussion, since it is based solely on my estimates and the conclusions to be drawn from this analysis don't change.

Referring to Figure 1, we can see a number of interesting things from these graphs. The curves have an odd, saw-tooth shape. Why? Let's think about it by studying the bus curve. Assume we are transporting people from Boston to New York. If we are transporting between 1 and 50 people, we need one bus, which gets 9 mpg. With 1 passenger, the passenger-miles/gallon is 9. With 2 passengers, it is 18, and so on. Between 1 and 50 passengers, the passenger-miles/gallon curve goes up linearly with a slope of 9 (I am making the simplifying assumption that for all modes of transportation, the fuel mileage, in miles/gallon, is constant, independent of the number of passengers). But when the 51st passenger arrives, you need another bus. So now you are using two buses to transport 51 people, increasing your fuel consumption by a factor of 2, so the passenger-miles/gallon is $\frac{9}{2}\cdot 51=229.5$, whereas at 50 passengers, it was $9\cdot 50=450$. As more passengers arrive, the passenger-miles/gallon curve increases again, reaching its peak of 450 again at 100 passengers. When the 101st passenger arrives, you need a third bus to transport 101 people, increasing fuel consumption by a factor of $\frac{3}{2}=1.5$ and passenger-miles/gallon drops to $\frac{9}{3}\cdot 101=303$. So, you can see why the curves have the saw-tooth shape they do: passenger-miles/gallon increases as you add passengers until you reach the capacity of the vehicle you are using, at which point you add another vehicle, increasing fuel consumption. Note that no mode of transportation can ever exceed the passenger-miles/gallon it achieves with one fully-loaded vehicle.

We see that an airliner (in this case, a Boeing 767) is roughly comparable to the SUV, while the small Cessna business jet lags everything else by a significant margin. Little wonder that airplanes are drawing increasing notice from scientists studying our climate stability problems. The advantage of a passenger car over an SUV is obvious, the hybrid even more so. But neither SUVs nor either of the cars, even the efficient hybrid, approaches the efficiency of trains or buses when moving a lot of people, which is why people concerned about the impact the transportation sector is having on our environment (and our national security, previously discussed) are so passionate about mass-transit modalities. And it is this large-economies-of-scale property of mass-transit that motivates me to urge you to use this type of transportation whenever possible.

Figure 1: Maximum Efficiency of Various Modes of Transportation

Figure 2: Estimated Average Efficiency of Various Modes of Transportation

Yes, you say, but I can get to work in my own car in 45 minutes (Can you? Have you taken traffic into account? Or the personal cost of commuting at odd hours to avoid that traffic?) and it will take 75 minutes to do the same trip by mass-transit. 75 is greater than 45, isn't it? Maybe not! You can be productive on a train or a bus, reading a book, working on your laptop, etc. You have much more limited options for productivity while driving a car (e.g., books on tape). In addition, if you are anything like me, driving is a stressful experience. As the roads become more crowded, rudeness and road-rage have become increasingly common. I find that the probability of something unpleasant happening on any individual trip in a car these days is distressingly high. 45 minutes driving a car is far more stressful for me than 75 minutes on a train or bus. So if you can afford the additional elapsed time (if, in fact, the elapsed time for the train is greater than that for the car), you may well accomplish more with less wear-and-tear on yourself (and your car) by taking mass-transit to work.

Let's look at another example, where we will compare several mass-transit options with each other and with cars.

Suppose you need to get to New York from Boston for an 11:00am business meeting. You have four choices: fly, drive your own car, take the bus, or take Amtrak.

Flying means getting to Logan Airport, usually about an hour from the Boston suburbs, at least an hour before flight time (they are getting more and more serious about airport security, thankfully), maybe more. Add about an hour from takeoff to touchdown at La Guardia, more if the flight is delayed (a common occurrence at La Guardia, the airport with the worst flight-delay record in the US). You now have 3 hours or more invested in this trip but you are at La Guardia, and you need to be in mid-town Manhattan. Most people take a cab, which is invariably driven maniacally (a long-standing tradition among NY cabbies). This will take the better part of an hour, especially during New York's extended rush hour (there are huge numbers of folks in New York who haven't read this paper or others like it and persist in clogging the Mid-town Tunnel, the 59th Street Bridge, and the Triborough Bridge with automobiles, despite New York's efficient, though not especially elegant, subway system). The net result is that you will get to your mid-town destination in about 4 or more stressful, hassle-filled hours. And airplanes are among the least fuel-efficient modes of transportation¹¹ (see Figure 1 on Page ). Total round-trip cost: over $500, including the cost of plane tickets, transportation to Logan, and the cab ride to Manhattan.

You could drive. Have you ever driven a car in the vicinity of, or in, Manhattan? You had better be truly battle-hardened. Have you thought about the unpredictability of your arrival time, given the vagaries of New York traffic? Have you thought about where you will park and what it will cost? Have you considered what it really costs to operate your car (the US government reimburses its workers at the rate of $.35/mile when they use their personal cars on government business; this is the result of the government's analysis of the true cost of operating a car (fuel, wear-and-tear, etc.) and the government does not have a reputation for being generous in matters like this)? We know about the fuel-efficiency of automobiles. Total one-way time: 4-6 hours, time totally wasted, compared to the reading and/or computing you could get done on a train, bus, or airplane (and, of course, you get to waste this time again on the way home). Total cost of the round-trip: $185 at $.35/mile, which includes $25 to park. I am not going to waste any more valuable keystrokes convincing you that this is not a smart plan.

You could take the bus. This is a highly fuel-efficient and cost-effective mode of transportation. Buses are not as roomy and comfortable for a trip as long as this when compared to trains, and they are subject to traffic congestion on the roads, but this is certainly a viable choice. Total one-way time: 4-5 hours. Total round-trip cost: $70.

You could take Amtrak. If you are in the suburbs west of Boston, you are most likely 30-60 minutes from the Route 128 station in Westwood. This station, recently completely rebuilt, offers plenty of parking ($10/day). You can arrive 15 minutes before the train departs. The Acela Express will get you from Route 128 to Penn Station on West 33rd Street in Manhattan in 3 hours, 15 minutes. You now have about 4-4.25 hours invested in the trip, and you are in Manhattan. The NY City Subway system is right there, to get you where you need to go quickly and efficiently, regardless of what is going on on the surface. The Acela Express costs about $120 each way. For about $65 each way, you can take the Acela Regional, which completes the trip in 3 hours, 45 minutes. Either way, I am confident you will find the train comfortable and hassle-free. Your trip will be slightly longer than taking the airplane, but only slightly (though you have somewhat less scheduling flexibility than you do with the air shuttles, which leave every half hour, between Delta and US Air, the Pride of Chapter 11), and you will arrive far less frazzled. Furthermore, you can use your cellphone on the train, and you have plenty of room to spread out and compute away on your laptop. You will also have an A/C socket to plug in the laptop's charger. Sleep is also possible, especially in the Acela Express' Quiet Car (where no cell phone use or extended conversation is permitted). We've already discussed the fuel-efficiency of trains. Total one-way time: 4.5 hours. Total round-trip cost: about $270 for the Acela Express, about $160 for the Acela Regional.

And, as an additional benefit, by using Amtrak you are adding to the growing chorus¹² calling for true high-speed rail in the US. This is especially important at a time when Amtrak is in precarious financial condition (due to unrealistic requirements imposed on it by the government, as well as past mismanagement; the current management, led by the tough, smart, no-nonsense David Gunn¹³, is excellent) and the Bush Administration, predictably, is providing little support¹⁴.

Automobiles

We've begun to explore our mass-transit options, and we should all try to use mass-transit whenever possible. But sometimes the only way to get around is in an automobile, if only to get to the train station. Automobiles are a marvelous invention and are invaluable to our lives. We just need to be much less indiscriminate in choosing them and using them.

Emissions

Automotive emissions are usually separated into two categories: smog emissions and greenhouse emissions. The former are substances such as particulates, oxides of nitrogen, benzene, and various other nasty substances. The latter is mainly a single gas - carbon dioxide, or CO$_{2}$.

Smog emissions are the cause of the orange haze that hangs perpetually over car-crazed Los Angeles (see Figure 3). These emissions can cause respiratory problems of varying severities, from asthma to lung cancer. Automobiles are now rated for production of smog emissions and these ratings are posted on a window of a new vehicle. Look for terms like LEV (low-emissions vehicle), ULEV (ultra-low-emissions vehicle), and SULEV(super-ultra-low-emissions vehicle). Achieving low emissions and good gasoline mileage simultaneously is difficult, so SULEV-rated, high-mileage cars are rare. The Toyota Prius is one.

Figure 3: Los Angeles

Carbon dioxide emissions are even a bigger problem than smog emissions, as they are thought to be a primary factor in global warming. Automobiles emit carbon dioxide in inverse proportion to their gas mileage. The worse the mileage, the more CO$_{2}$ produced per mile; it is that simple. If you are concerned about global warming, you should choose a high-mileage vehicle, and then drive it as little as your life-style permits.

Choosing an Automobile

In what follows, you will find that I frequently make praiseworthy mention of Toyotas. I am not a Toyota salesman and have no financial stake in anyone's purchase of any car. My bias for Toyotas comes from having owned four of them, two currently, and having been extremely satisfied with each of them. I've found them to be well-designed, well-made, reliable automobiles.

In choosing an automobile, I strongly believe that form should follow from function. Image is not everything, to disagree with Andre Agassi. We are causing too much trouble with our cars to let style dictate our automotive choices¹⁵.

I further suggest that you think hard about the functionality you require. Suppose most of what you need can be met by an environmentally friendly vehicle¹⁶, and you need something environmentally unfriendly only very occasionally, say, once or twice a year. In such a situation, I urge you not to buy for the infrequent case, which would mean inflicting excessive damage on the environment for no reason or benefit most of the time you use your vehicle. Instead, I suggest that you buy the environmentally friendly vehicle that serves your purposes most of the time, and cover the infrequent case(s) in other ways. For those occasions, rent a van, or an SUV if you must, or fly, or take the bus or the train. In other words, don't buy a Chevy Suburban if you are going to need to carry 9 people once or twice a year and use it the rest of the time to carry one or two people at 10 miles/gallon.

If you do need significant carrying capacity more often than very occasionally, your choices are station wagons, mini-vans, and SUVs. I suggest that you consider them in that order of priority. Why? See Table 1 and Figure 4 for a comparison of various characteristics of examples of these three classes of vehicles. Table 1 contains the raw data for each vehicle, obtained from MSN Carpoint. Figure 4 was generated from this data by dividing each data item in the table by the corresponding item for the VW Passat. For example, the height of the minimum price bar for the Volvo V70 Wagon is about 1.3, which is $30025 / 22550$. The reason for ``normalizing'' the data in this way is that it permits us to use one chart for this disparate data which, in its raw form, would require multiple vertical axes with greatly different scales (e.g., prices are in tens of thousands of dollars, whereas mileage is in tens of miles/gallon), necessitating multiple charts . It also lets us immediately see how the characteristics of the other vehicles compare with the VW. For example, one can readily see that the minimum price of a Lincoln Navigator is more than twice that of the Passat.

What can we learn from this figure? First, looking at the minimum and maximum mileage bars, as we move from station wagons through minivans to SUVs, the fuel mileage goes down drastically; the two biggest SUVs get roughly half the mileage of the wagons. Looking at the two sets of price bars, one can see that the price goes up significantly for the lower mileage of the SUVs. But passenger volume, capacity, and cargo volume of the SUVs is not significantly better than the wagons (e.g., the SUV offering the largest cargo volume, the Cadillac Escalade, provides 20% more cargo space than the Volvo wagon, the same passenger capacity, but gets 43% worse fuel mileage). One can also see that minivans offer great passenger capacity and room, somewhat at the expense of cargo volume. The following discussion explores the relative merits of these vehicles in more detail.

Table 1: Station wagons, Minivans, and SUVs

Make.Model.Type	Min.mileage	Max.mileage	Min.price	Max.price	Pass.volume	Pass.capacity	Cargo.volume
VW Passat Wagon	21	30	22550	38700	97.5	5	39.0
Volvo V70 Wagon	21	28	30025	36235	NA	7	37.5
Toyota Sienna Minivan	19	24	22550	28012	154.1	7	26.6
Chrysler Town and Country Minivan	18	24	24020	38755	164.9	7	20.0
Toyota 4Runner SUV	16	19	26335	36105	87.1	5	44.6
Lincoln Navigator SUV	11	16	48135	54310	NA	7	17.9
Cadillac Escalade SUV	12	16	49805	55370	122.1	7	45.7

Figure 4: Station wagons, Minivans, and SUVs

Station Wagons Station wagons provide good carrying capacity for people and gear, are very space-efficient, provide safe handling, and are more fuel-efficient than either of the other two choices. While wagons have been the primary victims of the SUV craze¹⁷, they are beginning to make a comeback. As previously discussed, a look at Figure 4 begins to give on an idea why. Wagons are very price-competitive with the other types of vehicles, and provide an excellent balance between fuel-efficiency, seating capacity, cargo capacity, and are the safest of the three types of vehicles. There are a number of good choices available. If you can afford one, Volvo is still a leader in automotive safety research, and their cars reflect this emphasis. BMW and Mercedes also make excellent, safe, fast (but expensive) wagons that provide top-notch handling, partly due to their almost perfect front-rear weight distribution, made possible by rear-wheel drive. Rear-wheel drive is a drawback, however, in snow, and if you live in one of the remaining areas where snow is still a factor, a front-wheel drive wagon might be a better choice. The VW Jetta¹⁸, VW Passat, and Audi are all worth consideration (but avoid the four-wheel drive option unless you are the rare person who has a strong reason, e.g., a very steep driveway, for electing it; it is expensive, it is a gas-mileage killer, and it reduces the performance of the vehicle). In the lower price ranges, Toyota makes a vehicle called the Matrix (essentially the same vehicle is also sold as the Pontiac Vibe). The vehicle is quite functional, and because it is a Toyota, it is likely to be well-made and reliable (I suspect the styling won't appeal to the older generations, who can choose other alternatives). Ford makes a wagon version of its highly praised Focus. There is also a Saturn wagon available. See Consumer Reports for recommendations.

Mini-vans If a station wagon doesn't provide sufficient passenger-carrying capacity, mini-vans are a good alternative. While not as fuel-efficient as wagons (despite the manufacturers' efforts to improve their aerodynamics, their width and height makes them hard to push through the air), they are superior to SUVs. There are many good mini-vans available; see Consumer Reports.

Sport Utility Vehicles I will say right at the outset of my discussion of SUVs that the only sensible reasons I can think of for owning one are either a genuine need for four-wheel drive and generous ground clearance¹⁹ (perhaps you live in rugged country, where you travel bad roads or off-road frequently, or there is a lot of snow), and/or a need for something that has the carrying capacity of a small school bus (perhaps you have an unusually large family that would overflow even a mini-van, so the largest of SUVs, an Excursion or Suburban, is your only option).

The appeal of muscular styling, enormous size, or the ego-feeding high driving position are not justifications for owning an SUV²⁰, in my opinion, nor is safety (again, see the DOT safety statistics; you will be surprised), nor is a steep driveway (you can get a four-wheel drive wagon from VW, Subaru, or Mercedes that will scoot right up your driveway and get far better gas mileage than any SUV). Why are SUVs to be avoided? They are extremely fuel-inefficient, space-inefficient, they cost more to operate, and they exhibit dangerous handling characteristics.

Why are SUVs fuel inefficient? They are trucks, built on truck chassis, and thus are extremely heavy. Sir Isaac Newton tells us that more weight requires more fuel to accelerate, all other things being equal. In addition, most SUVs are equipped with four-wheel drive, which is a double whammy. The extra machinery adds weight (Newton again) and that added machinery also adds rotating frictional losses, even when the four-wheel drive isn't engaged. The cost of this is significantly greater fuel consumption, for absolutely no benefit in the vast majority of uses of SUVs²¹. Lastly, the height and shape of SUVs, as well as their typically massive size, makes them un-aerodynamic. They are hard to push through the air, and thus they consume more fuel.

SUVs are space-inefficient. Figure 4 demonstrates that SUVs provide very little additional carrying capacity compared to a station wagon, either in terms of passengers or cargo, but they exact a tremendous additional penalty from the environment, because of their fuel consumption (e.g., a Toyota 4Runner carries the same number of passengers as a VW Passat, 14% more cargo, and uses between 24% and 37% more fuel).

SUVs cost more for certain types of maintenance than cars. Have you ever priced a tire for a big SUV? They are almost twice the price of tires for a car like a Honda Accord or Toyota Camry.

SUVs handle dangerously because they are heavy, high and narrow relative to their height. The resulting high center-of-gravity makes them famously prone to rolling over. Combined with their great weight, the immutable laws of physics say that they cannot be agile. A big SUV is the last vehicle I'd want to be in if I had to undertake an evasive maneuver at 70 mph. Sometimes the best way to survive an accident is to avoid having one. Test-drive a BMW wagon on the highway (doing some lane-changing maneuvers) and on a winding road; then do the same with a Lincoln Navigator (please be careful); you will instantly understand.

SUVs could also turn out to be very bad investments, if gasoline becomes scarce and prices rise as a result of turmoil or war in the Middle East. Nothing will change American automobile preferences faster than waiting on line to leave $100 at the pump (we saw this fickle behavior during the OPEC-induced oil shocks of the 1970s; the 12 mpg land barges people were driving gave way quickly to a huge demand for 50 mpg diesel VW Rabbits, which were selling for prices above MSRP). If this situation occurs, what do you think will happen to the resale value of SUVs?

So, what we have here are vehicles that consume great quantities of fuel per mile (costing you more money/mile than a car), emit CO$_{2}$ and smog gases at unconscionable rates, carry less than they ought to considering their fuel consumption, handle unsafely, and might be bad investments if fuel becomes scarce and expensive. And buying one provides the manufacturer and dealer with the greatest profit margin of any vehicle sold today, so you are paying extra for the privilege of owning a vehicle with this unique combination of bad characteristics. Why would anyone buy such a vehicle? Beats me! I think the history books will record the SUV stampede as one of the greatest triumphs ever of clever marketing and styling over an ill-informed and/or uncaring public.²²

Choosing a high-tech automobile

I also urge you to watch the developments in automotive technology. Things are changing rapidly. As I write this, there are two practical hybrid vehicles for sale in the US: the Toyota Prius and the Honda Civic Hybrid. Both of these vehicles, and especially the Prius, represent a significant leap forward in automotive technology. For those not familiar with hybrid technology, these cars are powered both by gasoline engines and electric motors, with high-capacity battery packs. It is a popular misconception that they need to be plugged in to recharge the batteries. This is not true. Hybrids never need to be plugged in. In fact, owning and driving a hybrid is virtually the same experience as an ordinary car. The difference is that hybrids deliver approximately 50 miles per gallon²³. For purposes of this discussion, let's focus on the Prius, the more technologically advanced of the two vehicles. The Prius has a small, 70 horsepower 4-cylinder gasoline engine, a 44 horsepower electric motor that develops an enormous 258 ft.-lbs of torque, and a 273.6-volt battery pack. Utilizing an extremely clever planetary power-splitting device that serves as a continuously-variable transmission, any combination of the gasoline engine and/or the electric motor can be used to power the car and to store energy produced by the gasoline engine to recharge the batteries (these decisions are made by the Prius' computer without requiring the slightest attention from you; you just sit back and drive). Furthermore, taking advantage of the fact that electric motors and generators are the same machine used in opposite ways (a motor takes electrical energy in and produces rotational energy out; a generator does exactly the opposite), the Prius is able to recapture some of the energy invested when it is accelerated up to speed, energy that is usually lost to heat when a car is braked to a stop by ordinary frictional wheel brakes. It does so by turning the motor into a generator, slowing the car by the effort to turn the generator, and storing the resulting electrical energy in the battery. This is called regenerative braking, and the energy thus recaptured can be used to help power the car via the electric motor, saving gasoline.

The Prius's computer also shuts the gasoline engine down when it is not needed, such as at stoplights, or when the demand for power is small, such as low-speed steady-speed driving on level ground, or when going downhill. In latter situations, the Prius is propelled solely by its electric motor. Prius enthusiasts refer to this as ``stealth mode''.

Whether in electric-only (stealth) mode or with the electric motor assisting the gasoline engine, some of the energy propelling the car comes from that recovered during regenerative braking. This is one of the factors that accounts for the Prius' extraordinary efficiency.

The Prius's gasoline engine is itself an engineering marvel. Unlike virtually every gasoline engine built in the last 100 or so years, it does not use the standard Otto 4-stroke system. It instead employs a variation known as the Atkinson Cycle, which was invented at roughly the same time as the Otto Cycle. The Atkinson approach addresses some of the problems that make gasoline engines less efficient than diesels. The Prius engine also employs an offset crankshaft to eliminate internal friction. If you are interested in the details, there is a brilliantly-done website put together by a gentleman who is both an engineer and a Prius owner. He did considerable research to learn how the Prius works (Toyota is not especially forthcoming with the details, for proprietary reasons) and has provided excellent explanations and animated diagrams that make it all clear, even to interested non-engineers. See http://www.channel1.com/users/graham/MyToyotaPrius/PriusFrames.htm .

The Prius automobile is an innovative design that makes extraordinarily good use of the available space. It is a small, Corolla-sized car, with nearly the interior room of the previous-generation Toyota Camry. It is designed to be extremely aerodynamic, having one of the lowest drag coefficients of any car available today. Furthermore, it is equipped with low-rolling-resistance tires that increase its fuel efficiency.

The Prius is very well-equipped - A/C, power windows, doors, good stereo, are all standard equipment, together with quality interior appointments and comfortable seats. Cruise control, CD player and/or changer, a GPS-based navigation system, and side airbags are available as options. The hybrid system provides powerful performance, and a top speed of over 100 mph. Toyota provides exceptional warranty coverage on this car and free 24/7 roadside assistance, to take the risk out of owning leading edge technology. The Consumer Reports frequency-of-repair statistics have been excellent for the two years the car has been available in the US. The car has been sold in Japan since 1997, and appears to have been quite reliable over that time period as well, based on what I've been able to learn on the Web.

As I said earlier, I am not a Toyota salesman and have no financial stake in anyone's purchase of any car. I do own a Prius myself and believe in the technology. I think anyone in the market for a small sedan should consider it.

I would add that it behooves anyone contemplating an automotive purchase in the next year or two to watch developments closely. Things are moving rapidly in the hybrid arena. New hybrids will be appearing in the next two model years (it is likely that Toyota will introduce a redesigned Prius and there is speculation concerning a hybrid Highlander), so the range of choices will widen.

Fuel cells, a new technology that uses hydrogen as its fuel and emits only water vapor²⁴, are about to be introduced in automobiles on a limited basis (again, Toyota is leading the way). I don't expect fuel cell automobiles to be in wide use in the US for 5-10 years (we have a lot of work to do to establish the needed refueling and repair infrastructure), and thus purchase of a hybrid is a reasonable interim strategy.

Driving your automobile

Having chosen the most environmentally friendly vehicle that meets your functional needs, let's discuss some ways to minimize its negative impact on the environment.

The best way to minimize the environmental damage you do with your car is to drive it as little as possible, consistent with your transportation needs. I am not suggesting that you buy a car and leave it in the garage. Rather, I am suggesting that you can reduce your automobile use with little or no sacrifice through a combination of use of mass-transit (in situations where that is a practical alternative), and elimination of wasted driving.

If mass-transit is a practical alternative for you in commuting to work, or for periodic outings to the city, please consider it. It will save wear-and-tear on your car, reduce the rate at which you accumulate miles on the car (thus deferring the time at which you have to replace it), eliminate parking fees, reduce fuel costs, and, of course, reduce environmental damage. The true cost of driving (remember the US Government's $.35/mile) is almost always greater than the cost of the train or bus.

You should also try to eliminating superfluous driving. Call ahead before running to the store to get something, if you are not certain they have the item you want. Consolidate your trips; one trip to town to go to the food store, the hardware store, and the drugstore is much better than three, and it saves you time, effort, and money, as well as helping the environment. Plan outings with your spouse to the city so that you don't run two cars to the same destination and back if you aren't leaving at the same time. Trains or buses can help here: one person takes the train and the other drives in (or, better yet, both take the train) and you go home together.

The extreme case of superfluous driving is running the engine in a stationary car (during which you are getting exactly 0 mpg!):

• As we discussed earlier, don't leave the engine running when you run into the store or post office.
• Don't warm up the engine for extended periods when you start it on a cold morning. This outdated practice is bad for the car, bad for your wallet, and bad for the environment. Instead, wait 10 or 15 seconds after the engine starts to begin moving, and then drive slowly for the first few minutes while the engine warms up.
• Stopped at a railroad crossing? Turn off the engine.
• Try to avoid sitting for extended periods in a stationary car on a hot day with the engine running to keep the air conditioner going. This is a tremendous waste of fuel.

Speed

Speed not only kills, it uses fuel, a lot of fuel. Why? Go back to your high-school physics. Remember this?

$$E = \frac{1}{2}MV^2$$

Well, maybe it's been awhile, or maybe you just hated physics. This is the formula for kinetic energy. It's the the energy you have to invest in a car of mass M to get it going with velocity V. That energy comes from burning gasoline. The primary thing you need to notice is that the velocity is squared. This is bad if you like speed. Why? Because it means that the fuel required to accelerate a car to 60 mph is four times that required to accelerate the same car to 30 mph (quadratic growth), not twice as much (linear growth), as some might guess. The fuel required to maintain a constant speed (which means fighting aerodynamic drag and other forms of drag) also grows faster than linearly with increases in speed (i.e., it will require more than twice as much fuel per mile to maintain a constant 60 mph as it would to maintain a constant 30 mph).

What does this tell us? Driving fast causes disproportionate environmental damage, as well as fuel costs. So, it makes sense to drive as slowly as you can consistent with your time constraints, practicality, and safety (driving 30 mph, even in the right-hand lane, on a four-lane highway that is generally moving 65 mph, is dangerous). And time constraints can be dealt with by leaving a little earlier. Here the non-linear relationship between speed and fuel consumption works in your favor. Driving 10% slower means your trip will take about 11% longer, but you will use perhaps 15% less fuel²⁵.