By Eunice L. Alexander, Ready for 100 Chester County volunteer, Southeastern PA Group
There are many ways we can reduce our energy consumption and save money every year, as well as enhance road safety, prevent avoidable wear on our vehicles and reduce greenhouse gas emissions (GHGs). Traditionally, gasoline and diesel fuel consumption has generated just over one-quarter of our country’s total energy-related carbon dioxide (CO2) emissions, [1] so cutting GHGs in the transportation sectors is worth our whole-hearted pursuit.
Energy usage in vehicles is determined by the type of vehicle, the source of energy and the way it is driven. [2] [3] Mass, aerodynamics, friction, accessories [3] and the efficiency of automotive parts are key factors. Although this article focuses on the driver of a gas- or diesel-powered vehicle or a plug-in hybrid, the recommendations are generally relevant to those driving electric vehicles (EVs), plug-in hybrid EVs (PHEVs) and even flexible fuel vehicles (FFVs).
Under “normal circumstances” some 147 million gallons of motor gasoline are burned by passenger vehicles in the United States every day. [4][5] Consider that a four-door sedan with listed mileage of 35 miles per gallon on the highway could attain 27 mpg by being poorly maintained and driven aggressively, but 37 mpg if driven efficiently.[6] Mindful driving would cut the energy consumption by our vehicles substantially with no change in fleet composition. This is indeed part of the current low-hanging fruit in energy conservation.
Burning one gallon of regular gasoline directly produces 19.64 lbs. of CO2 (5.35 lbs. of carbon), but 10% ethanol content (E10) gasoline is commonly available today. [7][8] This formulation is 3.5% less carbon intensive than regular, emitting 18.95 lbs. of CO2/gallon (5.17 lbs. of carbon). [1] E85 fuel, also called “flex fuel” because of its variable high ethanol content, is less common, and its ethanol content varies somewhat with the seasons. In terms of burning diesel fuel, about 22.38 lbs. of CO2 is released by the burning of one gallon. Of the formulations for diesel-fuel powered vehicles, B20 (20% biodiesel and 80% petroleum diesel fuel) is commonly sold; if this is burned, “then about 20.22 lbs. of CO2 are produced.” [8][9]
Now, let’s examine the impact on fuel economy of the 70-mph speed limit posted by the PA Turnpike Commission in May, 2016, which applies for much of the Turnpike’s length. We compare two 100-mile trips, theoretically flat to slightly rolling terrain, made by a 2012 Subaru Impreza AWD with automatic transmission, 4-cylinder engine. One trip is driven at 70 mph, the other at the speed limit set for the national energy crisis of the mid-1970s. In January 1974, President Nixon instituted a national highway speed limit of 55 mph. [10] We further compare these results with the same 100-mile trip at these speeds, but this time travelled by a common commercial vehicle: the 2012 Peterbilt 389, a tractor trailer (“18 Wheeler). [11]
This Subaru averages 35 mpg at 55 mph, 3% less than that (34 mpg) at 60 mph, 8% less (32 mpg) at 65 mph, 17% less (29 mpg) at 70 mph, and 23% less (27 mpg) at 75 mph. [6] [12] The 55-mph 100-mile journey consumes 2.86 gals. of gasoline; it takes 3.44 gals. at 70 mph. Therefore, an extra 0.58 gallons of gasoline is combusted on that trip to drive the speed limit on today’s Pennsylvania Turnpike as compared with the limit required in a time of national emergency.
Although about 40% of trucks in use in the United States are single as opposed to a combination-unit trucks like this tractor trailer, the fuel economy of the commonly seen (again, traditionally) charter buses on the Turnpike such as the MCI D4505 for this year is comparable. [13] [14] The partially well-loaded Peterbilt tractor trailer with dual tires perhaps averages 7 mpg at 55 mph.[11] The general rule of thumb of lowering fuel economy by 0.1 mpg for every increase of 1 mph yields 5.5 mpg at 70 mph. [15] The 55-mph, 100-mile journey consumes 14.3 gals. of gasoline; it takes 18.2 gals. at 70 mph. Therefore, an extra 3.9 gals. of gasoline is combusted for this common type of truck hauling goods at the speed limit on today’s Pennsylvania Turnpike as compared with 55 mph.
During Fiscal Year 2017-2018, the equivalent of 59.35 million such 100-mile trips were made by passenger vehicles and 59.47 million such trips made by commercial vehicles. [16] Choosing to make this Subaru represent passenger vehicles and this Peterbilt the representative commercial vehicle, we multiply the above miles traveled (in millions) by the extra gallons of fuel consumed by traveling this 100-mile stretch at 70 mph. We then multiply the results (34.4 million gals. for passenger and 231.9 million gals. for commercial vehicles) by their respective fuel’s CO2 in lbs./gallon (18.95 for E10 gasoline and 20.22 lbs. for B20 diesel fuel). Adding the two amounts of pounds of CO2 in millions gives a total of 5.34 billion lbs. of extra CO2 release, which constitutes 2.4 million metric tons (MMT).
Don’t normally exceed 60 mph on the highway; do “drive 55” mph on the highway where possible.
The “Drive 55” slogan was a key part of our energy plan during the fallout of the OPEC oil embargo in the 1970s.[10] While every vehicle is different, the fuel economy of most cars, vans, pickup trucks and SUVs typically peaks between 30 and 50 mph. [17] In highway driving, the loss of fuel economy is mainly due to aerodynamic drag; and merely lowering one’s speed by 5 to 10 mph saves fuel significantly. [3] Over 50 MPH, fuel efficiency decreases quite rapidly in most cases, because a car encounters ever more wind resistance and the tires more rolling resistance.” [17]] [18] Most vehicles travelling 75 miles per hour on the Pennsylvania Turnpike waste 20% of the fuel that they would consume going 60 mph. [17] According to Simon East, CEO of DriveGain, staying below 55 or 60 mph only adds a few minutes to the average travel time; [19] so, to save gas and maximize road safety, stay at or under the speed limit.
Finally, to reduce how hard the engine must work, shift into the highest appropriate gear. For the highway, the transmission should be in overdrive [4] On a manual transmission, pay attention to the revolutions per minute (RPMs) as you accelerate, shifting to higher gears as soon as possible. [20] Truck drivers who block shift, by going from 2nd gear to 5th gear, for example, and other techniques improve fuel economy. Overall, good driver training is essential for those operating large trucks, like tractor trailers. [15]
Don’t alter your driving speed frequently; do drive as smoothly as possible.
Aggressive driving habits such as gunning the engine, speeding, screeching around corners, and jamming on the gas pedal are major fuel wasters. Tests consistently find this to be key behavior to avoid for energy-efficient driving. In fact, how smoothly you drive makes much more of a difference on gas mileage than how fast. Smooth driving can improve the fuel economy of your vehicle by 15%–30% at highway speeds and 10%–40% on slower roads. [21] [22] [23] [24] By watching what pedestrians and other vehicles are doing, and anticipating what they might do next, you can drive more smoothly and require less energy. It’s also safer to drive this way. [4] [17]
The power needed to accelerate any vehicle primarily depends on the mass of the vehicle. Try to accelerate gently. Terry Penney, a technology manager at the U.S. Department of Energy (DOE) National Renewable Energy Laboratory in Colorado, suggests that we “drive as if there’s an egg between your foot and the gas pedal.” [18] Coast when you can by increasing your following distance and look ahead to let the vehicle slow down naturally. [3] [17] Hybrid vehicles use friction braking but take advantage of the vehicle’s regenerative power capability. [3] And, of course, braking any vehicle cuts its forward momentum and then requires more energy-draining acceleration.
Smooth cornering and the other good habits mentioned also reduce wear-and-tear on your engine, transmission, brakes and tires and drain on your battery. [18]
Don’t use cruise control when driving on highways with steep grades; do use it if driving on fairly flat terrain.
Cruise control is generally an asset in highway driving. Of course, we must be mindful of the right conditions under which to use it. First of all, we must acknowledge that even the best drivers unnecessarily waste fuel by varying speed. [3] When should cruise control be used? Consider turning it on for long stretches of highway driving. It can help you keep a steady speed and thereby save fuel. [14] Do turn it off in areas with steep hills, however; cruise control’s efficiency is lost in such terrain. [25] It is also energy efficient to allow gravity to do the work. In hilly areas and where traffic permits, let your car slow down going uphill and pick up its momentum on the downslope. [17]
Cruise control systems also can vary in design quality; better systems do not require surges to climb a hill. [26] They also minimize the power needed to retain a selected speed. 26] If your cruise control is not high quality, you should stick to using it only on fairly flat highways. [4]
Don’t delay basic car maintenance and/or use the wrong fuel octane-level; do take good care of your vehicle and have the engine tuned-up and other basic maintenance performed at the recommended frequency.
Good vehicle maintenance conducted on a sound schedule, including oil changes and replacing the air filter and spark plugs, is the best way to improve energy efficiency. [27] Also, the fuel injectors and throttle body should be cleaned regularly. [28] Just 10% of cars, especially poorly functioning ones, cause most air pollution from cars. [4]
Part of good maintenance is washing off the vehicle’s exterior; [3] even plain water and a sponge accomplish this quite well, applying just a little degreaser where needed. Dry any areas that are prone to rusting.
Use the manufacturer recommended engine oil to get the most from your engine and not cut as much as one-tenth of your fuel efficiency accidentally; oils with organic and other friction modifiers exist and may be warranted. [3] [27] Using the manufacturer's recommended fuel octane matters, too. Smaller, modern engines might use turbochargers to produce more power and need a higher-octane fuel for proper combustion; this premium fuel is more expensive and does not improve the fuel economy of other engines, however. [3]
Have the wheels correctly aligned, and keep your tires properly inflated. [3] Under-inflated tires can be dangerous. They run much hotter and are more likely to fail at high speeds and also increase braking distance. [18] [20] [21] [29] DOE has calculated that a billion gallons of gasoline could be saved in the U.S. every year simply by having tires properly inflated. [29] As much as 4% extra fuel was consumed by cars with tires 8 pounds under-inflated; this amount was also estimated to cut 6,000 miles off the life of tires. [17] [30] Therefore, do measure the pressure of your “cold” tires; monthly is the frequency recommended by experts. [18] [27] [29]
Which tire should you buy? In addition to affordability, look for good all-around performance in braking, handling and resisting hydroplaning; after that, consider its rolling resistance, which is the friction of tires on the road, before purchase. [3] Naturally, this friction increases as tires get larger and vehicle weight goes up. [3]
Although the sensor might be bad, an engine light coming on should be checked out as soon as possible. [3] It can point to an additional problem: one with the fuel emissions system. [3]
Maintain your cooling system. Turning on the air conditioner for at least a few minutes monthly helps keep the internal rubberized parts “lubricated.” [28] Using the AC on hot summer days can sometimes cause overheating. [28] If this happens at stop lights or in slow traffic, a mechanic should check the fan clutch; if overheating is a general problem, the cooling system (the coolant tank, radiator cap, radiator, water pump, and heater core) should be examined for leaks. [28] The aluminum condenser coil on the front of the radiator should be cleaned every spring with a non-acidic cleaner to remove grit and insects. [28] An air conditioner’s efficiency also declines as it ages, because it has to run longer to maintain any setting; its refrigerant (CFCs (chlorofluorocarbons)) can also leak. [28] One mechanic noted that you should take the vehicle to a professional for service if you see oily deposits around the fittings of the A/C. Any leak of this refrigerant would lower efficiency. [28]
Don’t maximize your comfort with your vehicle’s air conditioner and heating system; use them sparingly, only as really needed.
This discussion will focus on cooling but also generally applies to heating of the vehicle’s cabin.
The most critical task is to pay attention to solar power by practicing passive cooling (and heating) of your vehicle. [30= [30] On hot days, try to wear lighter clothing or change at work, and roll down the windows right away; the hotter the car is, the harder the A/C system has to work. The more work a system must do, the more energy consumed. [30]
Using an air conditioner (A/C) requires mechanical energy from the engine to spin the A/C compressor, thereby burning some fuel, or, in an EV, requires power from the battery. [28] Automotive air-conditioning has become more efficient by drawing much less power than older units did, but this is still true. [31] Turning on your air conditioner could worsen gas mileage just 3%, which adds up when we consider the amount of usage in just the U.S., let alone world-wide. [17] [18] [30] In a 2008 Ford Focus, Honda Accord, and Subaru Forester, lower mileage was detected with A/C running to combat temperatures even in the low 70s degrees F outside. [18] On scorching hot days, setting an A/C to minimum temperature makes it run hard and continuously. This can then increase fuel consumption as much as 20%. [17] [28] EV drivers will find the need for more frequent charging of the battery, and these batteries have a certain number of recharges associated with its life cycle.
Less than rigorous thought has thus far gone into the issue of energy inefficiency of windows versus A/C. The devil appears to be in the details. Deciding whether to choose A/C or open windows depends on driving speed, wind speed, terrain, vehicle size and aerodynamics, and, so, is complicated. [27]
Open windows are generally thought to introduce an unacceptable aerodynamic drag at speeds above 40 or 45 mph, causing it to use more energy than if the windows were closed. [28] An A/C compressor running constantly or intermittently does cause a small drag of its own; [28] however, at speeds greater than 45 mph, the horsepower and torque of these speeds easily operate it, and this consumption is extremely low. [28] Of course, drag from the “open” windows also depends on how open the windows are!
So, the common wisdom is to roll up your windows and use your air conditioner at speeds above 40 mph (on higher-speed secondary roads and highways). [3] [17] [30] Researchers at Oak Ridge National Laboratory in Tennessee who compared the performance of a Ford Explorer and a Toyota Corolla, unsurprisingly, found that energy consumption was the lowest when AC was off and the windows were up. However, at speeds slower than 75 mph, it was more efficient to have the windows down. [21] A/C usage lowered energy efficiency in the Corolla, but not for the larger cabin of the Explorer which was “harder to cool.” [27] However, a 2008 Consumer Reports test of a Honda Accord at 65 mph with the windows down versus running the A/C revealed no measurable effect on fuel mileage. [18]
Tests by Edmunds at 65 mph with the A/C on and the windows up versus the A/C off and windows down revealed no measurable difference in mileage with the windows down. Similarly, in Consumer Reports tests with a Honda Accord, using air conditioning while driving at 65 mph reduced gas mileage (by more than 3 mpg), but opening the windows at 65 mph caused no measurable loss of efficiency. [21] [27] Edmunds’ testing of an SUV with open windows likewise had no discernable impact on the mileage, but opening its sunroof did lower efficiency. [21] Their 65-mph testing of a full-sized truck (Toyota Tundra) yielded 10% better gas mileage at with the windows down than with using the A/C. [27]
Plan B: Windows often need not be open much to attain sufficient comfort, especially when coupled with use of the flow-through ventilation system even on the highway. [17] [28] However, heat, humidity and noise can be intolerable; [28] levels of ozone and other air contaminants can also be unacceptable. Light use of air conditioning may provide tolerable comfort and cleaner air and consume a low amount of energy. This energy use then would be considered in a carbon-footprint analysis by the driver or occupants and potentially offset. If you do use air conditioning, prevent bringing in hot air that will require cooling by using the recycle-inside-air (recirculate) option for the vehicle. [17] [30]
Don’t lug unnecessary cargo weight in and on your vehicle; do travel as lightly as you can.
Avoid carrying unnecessary weight. The less it weighs, the less hard your engine must work and the less fuel your vehicle will use. Check the trunk and back of the vehicle for unnecessary items that may be safely stored elsewhere. [32] You might not choose to shave about 2% off your fuel efficiency by keeping an extra 100 pounds of salt, sand or sports equipment stashed in your vehicle. [17]
Some opt to fill their gas tanks only halfway to lighten the load. A half a tank of fuel could weigh as much as fifty pounds or as little as twenty pounds and allow more fuel economy; but only partially refilling requires more frequent trips to the gas station and probably does not justify the infinitesimally small gain in mileage. [33] Accordingly, you can minimize evaporation of fuels by not pumping during the heat of the day. [2] Also, leave a bit of room in the tank for expansion, and replace the gas cap tightly. [4] And, it is a myth that the most economical time to buy gasoline is the cool of the morning for highest density, because gasoline is normally stored in the cooler underground.
At highway speeds, more than 50 percent of needed energy automatically goes to overcoming wind resistance, so avoid carrying unneeded things on the roof. [30] Hauling cargo on your roof significantly lowers fuel economy. A roof-top cargo box, depending on the design, can reduce fuel economy by 2 to 8% in city driving and 6 to 17% on the highway. [24] [34] At highway speed, a Nissan Altima carrying two mountain bikes on the roof lost 13 mpg, going from 46 mpg down to 33 mpg; a Toyota RAV4 lost 7 mpg, dropping to 32 mpg from 39 mpg. [30] Note that you can deduct 10 to 25% off your efficiency by traveling this way at 65 and 75 mph, respectively. [24] [34]
Streamline your vehicle by taking off roof and bicycle racks that will not be used for a while. Merely driving with an empty roof rack caused the Altima to lose 5 mpg and the Toyota 2 mpg. [19] The Altima lost 12 mpg with the bikes on the hitch-mounted rack, while the RAV4 mostly hid them and was down only 5 mpg. The bikes stuck out to the sides of this sleeker sedan, which created extra drag. [2][19] A roof-top cargo box lowered the Altima’s mileage by 9 mpg and the RAV4’s by 5 mpg. [19]
Finally, at the risk of being a real downer, extraneous objects on vehicles like antlers and noses can raise your spirits but lower your energy efficiency; flags particularly maximize the drag. [3]
Don’t buy a larger vehicle than you need. Do select as compact a vehicle as you need and as is safe for you to drive.
Consider buying a new or newer-than-you-have used car. Technologic improvements are happening at a higher rate than in the past. [3] American fuel-economy regulations have been relaxed but advancements that impact fuel economy are available in good automotive choices. [3]
Unencumbered by expensive gasoline, many Americans have purchased larger vehicles in recent years; in 2018, sales were 2 to 1 light trucks over cars, according to data from Kelley Blue Book. [3] These large vehicles consume more energy than small ones; for example, the impact on fuel economy of driving a large SUV versus a compact is like driving 75 versus 55 mph. [19] Most SUVs gas mileage is 20-25 MPG compared to 30 to 40 mpg for sedans. [30] The emissions pumped into the atmosphere by SUVs (and light trucks), all else being equal, are higher. [4] Furthermore, the lifespan of the more costly tires of an SUV is roughly 30,000 miles versus 50,000 on most sedans. [35]
An all-wheel or four-wheel drive vehicle will burn more fuel than a two-wheel drive car because there are increased drivetrain losses. [3]
The past decade has seen the rise of lighter tractor trailers and other commercial vehicles. Improvements have been made in aerodynamics, tire rolling resistance and other factors. [15]
Don’t idle unnecessarily; do turn off the engine if you have to wait more than a minute and can safely do so.
Oddly, idling consumes more fuel than restarting the engine. Traffic-permitting, turn off your engine if you have to wait more than a minute or two. [20] [36] And avoid drive-thru service unless safety suggests otherwise. Instead, park and go into the building or to an outside window or ATM. [3] Idling can use a quarter to a half gallon of fuel per hour, depending on engine size and air conditioner use. [17]
The fuel-injected, electronically controlled drivetrains in modern vehicles do not require warming up before driving in cold temperatures. [18] If it’s bitterly cold, a 30-second “warm-up” before shifting to drive is adequate. [37]
Don’t waste fuel when doing errands; do plan ahead.
Call ahead as necessary to make sure your trip won't be wasted. [4] Shop around online, not in the car. [18] Plan ahead and reduce the distance you travel. [24] Combine short trips to save time and money, especially in cold weather. Short trips per mile can use twice as much fuel as a multi-purpose trip. [4] [30]
Choose feasible routes that avoid the stop-and-go traffic during peak commuting hours, road construction and accidents whenever possible [4]. Use four-lane highways when you can as these allow better flow. [17]
If ordering online, try to place one larger rather than two small orders to minimize vehicle miles traveled (VMT). Choose vendors that are closer to you, if possible.
Don’t ignore your fuel efficiency; do use available feedback to improve your driving and help your vehicle.
Besides keeping track of your gas mileage, driver feedback devices, like dashboard indicators and drive assists, did help most drivers lower their fuel consumption by 3-10%.[4] [38] A 2018 study by the National Center for Sustainable Transportation found that some drivers saved 15% more fuel by taking action prompted by display feedback. [17] 24]
Don’t drive unnecessarily, especially alone; do drive less.
Consider whether you can car- or vanpool, take available public transit, walk or ride a bike. [4] In 2018, three-quarters of people drove alone when going to and from work. [39]
Each day that millions work from home reduces the amount of fuel used by 20%. [17]
Take the free online ecoDriving course and play the Auto$mart Game to learn more about how fuel-efficient driving can help you save money and reduce your greenhouse gas emissions. [16] 2020 Challenge yourself!
If you'd like to promote idle reduction in your area, the Clean Cities IdleBox Toolkit can help you get started.
[NOTE of May 29, 2020: The Union of Concerned Scientists’ (UCS) Catalyst publication (Vol. 20, Spring 2020) has just reported relevant research despite being pre-pandemic by UCS Senior Analyst Elizabeth Irvin in its article, “Ride-Hailing: convenience at what cost?'' by Jiayu Liang. Although she previously has found that ride-hailing fills a gap in areas with low car ownership and poor access to mass transit, Irvin’s report, “Ride-Hailing Climate Risks”, provides some stark data and conclusions.
In brief:
- “Deadheading” causes the release of 47% more carbon than that from a private car. As with taxis, this is the extra miles driven that customers do not observe.
- Riders are migrating from biking, walking and taking the bus, carpooling and other options and even from remaining at home to rides from Lyft, Uber and other companies much more than was expected. Those changing their habits this way were more than a quarter of Californian ride-hailers surveyed. Irvin’s team estimated 69% more pollution generated in this way. If the trend persists.
Mitigating actions include:
- choose a “pooled ride” as soon as this can be safely done;
- request a PHEV or battery-powered EV; a ride-hailing EV would possibly reduce emissions three-fold compared with a private EV;
- apply smart measures to incentivize the desired changes by riders and companies (e.g., steps taken by the City of Chicago, suggestions by Elizabeth Irvin and campaigns such as #ElectrifyMyRide on Twitter).]
All references can be found here.
This blog was included as part of the Spring 2021 Sylvanian newsletter. Please click here to check out more articles from this edition!