Saving Fuel - Hypermiling Plus A Detailed Look At How Much Fuel Is Used While Idling

 With fuel prices at their highest numerical value ever (but still below the highest inflation-adjusted value ever of $5.37 per gallon), there is increased interest in electric vehicles. However, for drivers who are unable or unwilling to buy a new car, there are numerous ways to increase one's existing vehicle's fuel economy.

 There are the familiar tips like keeping your engine tuned up and your tires properly inflated, but hypermilers go far beyond the usual. Wayne Gerdes, who coined the term hypermiling, has broken several fuel economy records (including his own) in normal combustion vehicles, such as getting over 81 mpg in 2015 in a diesel VW Golf TDI rated at "only" 45 mpg highway by the EPA - an 80% improvement. While that car was provided by VW for the attempt, he got 59 mpg in his own non-hybrid used 2005 Honda Accord back in 2007 (depending on the engine/transmission combination, that year's non-hybrid Accords were rated at between 27 and 31 mpg on the highway, so his improvement's between 90-119%). The same techniques work to extend the range of EVs: during an LA to NYC cross-country record attempt, "Gerdes at times nearly doubled" the 225 mile EPA range of the 2021 Porsche Taycan he was driving - and spent less than $77 at charging stations for the entire 2800 mile trip. Although there are many approaches to hypermiling (such as this or this or this; the best single list I've found yet is this), some could be dangerous, like drafting other vehicles or shutting off the engine while coasting.

 Personally, I've been focusing on minimizing time spent accelerating (in other words, getting up to speed quickly, as traffic permits) and maximizing time spent coasting (while keeping the engine on!), and also driving in the slow lane on the highway with my cruise control set about 5-10 mph below the speed limit. For several months now, my average fuel economy is up to around 35 mpg calculated from miles between fill-ups divided by gallons added until the pump shuts off. Based on my mix of more highway than city driving (about 36% city / 64% hwy), that same combination of the EPA city/highway ratings for my car (21/29 mpg) should be about 26 mpg. That works out to a roughly 35% improvement - not as impressive as Mr. Gerdes but not bad at all for a casual and safe approach. The two approaches I'm going to add next are trying to time my arrival at intersections when the light turns green (braking gently earlier if necessary, but again, traffic permitting) so as to minimize accelerating from a standstill, and starting to move immediately after starting the engine when possible and shutting off the engine immediately upon parking.

 While I already tend to avoid sitting in drive-thru lanes, seeing images on the news of long lines of cars waiting at gas stations had me wondering how much fuel is wasted while idling. The only two sources I've found that appear to show reliable data are from Argonne National Laboratory, which lists a few specific passenger cars and numerous types of heavier vehicles (see their Excel worksheet for details), and a Complete Use article that mentions specific engines from two other passenger vehicles. To summarize their data for passenger vehicle gasoline engines with no load (i.e. not running the air conditioning or other accessories):

• Ford 2.0 liter:     0.16 gallons/hour, or 0.080 gal/hr per liter of engine size
• Ford 4.6 liter:     0.39 gallons/hour, or 0.085 gal/hr per liter of engine size
• Subaru 2.0 liter: 0.165 gallons/hour, or 0.083 gal/hr per liter of engine size
• Honda 3.5 liter:  0.3 gallons/hour, or 0.086 gal/hr per liter of engine size

 What's interesting is how close the numbers are for each liter of engine size, averaging about 0.084 gallon/hour per liter of engine size. This number allows one to estimate how much money is wasted by standing still with the engine on. Each 20 minutes of idling (to use one third of an hour as an example) thus burns about 0.028 gallon per liter of engine size. At the current national average gas price of $4.289 per gallon (as of March 17, 2022), that times 0.028 gallon equals about 12 cents every 20 minutes, per liter of engine size. As an aside, while I'm focusing on the financial aspect, those concerned with carbon should note that 0.028 gallon of gasoline produces about 249 grams or nearly 0.55 pound of CO2. Therefore, every 20 minutes, the fuel consumption, cost, and emissions are:

1. For a 1.0 liter engine: 0.028 gal/0.106 l, $0.12, 0.55 lb/249 g CO2
2. For a 2.0 liter engine: 0.056 gal/0.212 l, $0.24, 1.10 lb/499 g CO2
3. For a 3.0 liter engine: 0.084 gal/0.318 l, $0.36, 1.65 lb/748 g CO2
4. For a 4.0 liter engine: 0.112 gal/0.424 l, $0.48, 2.19 lb/993 g CO2
5. For a 5.0 liter engine: 0.140 gal/0.530 l, $0.60, 2.74 lb/1.243 kg CO2
6. For a 6.0 liter engine: 0.168 gal/0.636 l, $0.72, 3.29 lb/1.492 kg CO2

For intermediate or larger gasoline engines, just interpolate or extrapolate as the case may be. (Note, while the cost is variable, depending on the price per gallon, the emissions are directly proportional to the volume of fuel consumed.) What the above numbers mean for someone with, say, a 2.0 liter engine waiting in line to buy gas and buying 8 gallons, every 20 minutes spent idling is like adding 3 cents to the price per gallon. If they buy less, say 6 gallons, they're adding 4 cents to the price per gallon. For bigger engines it's proportionately higher.

 Use this information as you see fit. For me, it's a good incentive to continue to avoid idling as much as possible. Best wishes with your own fuel savings!