Energy Efficiency of Food and Personal Transportation in Rural and Urban Environments

Used under CC BY-NC-SA 2.0 license. Photo by flickr user LN.A thought experiment: there are two population centers, one of which is a relatively small town of 50,000 and the other is a major metropolitan area of 1.5 million. The smaller town, Smallsville, has a vibrant farmer’s market where for the sake of simplicity 100% of the population buys their food. The larger town, Bigsville, has no farmer’s market and 100% of Bigsville’s residents buy their food at major grocery stores. At first blush one would think that the citizens of Smallsville with their locally sourced food would use less energy than the residents of Bigsville who rely on long supply chains of 18 wheelers for their food.

This is not necessarily the case.

First, let us consider other factors besides food that could impact the energy consumption of the residents of Smallsville and Bigsville. Beyond food, what else could these residents be using energy doing? There are many durable goods – cars, refrigerators, dining room sets – that people in the developed world, regardless of how large a community they live in, consume. These durable goods, at least in the modern city structure, are rarely manufactured near the point of sale and thus travel great distances no mater if the buyer lives in Smallsville or Bigsville. Likewise, many nondurable goods – clothing, shoes, office supplies – are also made far from the point of sale and thus the energy consumption of both manufacturing these goods and transporting these goods to market is a wash when judging the relative energy consumption of Smallsville residents and Bigsville residents. This leaves us with two activities that require energy: food transportation and personal transportation.

In other words: for the sake of argument these are the two areas where energy use will differ between the two populations in question is food transportation (farmer’s markets versus big grocery stores) and personal transportation (cars versus urban alternatives).

Also for the sake of argument we will be ignoring the last mile problem of the consumer getting the food from the point of sale back home. If it helps, consider the calculations on personal transportation to take some of the slack that this oversight creates.

Food Transportation
As mentioned before, 100% of Smallsville residents depend on locally grown food which is harvested no more than 100 miles away. This super popular farmer’s market is supplied solely by small, private farmers. The average farmer bringing his goods to Smallsville will most likely do so in his trusty truck and trailer. A recent model year Ford F150 has a GVWR of 11,500 lbs and capacity for an additional 2,900 lb payload in the truck bed. A good quality trailer weighs 2,400 lbs. The total payload of this truck is (11,500 – 2,400) + 2900 or 12,000 lbs. The fuel efficiency for such a truck without trailer and without anything in the bed is 23 miles per gallon. Because we cannot test the fuel efficiency of the truck with a full load, we will say the Smallsville farmer’s trucks are able to attain 23 mpg despite being fully loaded. We are also saying that 100% of the road from farm to farmer’s market is highway allowing the farmers to travel at 55 mph for maximum fuel efficiency.

The distance between farm and market is 100 miles which means the farmer must drive 200 miles to complete the trip, there and back. The amount of fuel he would use bringing his 12,000 pounds of goods from farm to market then driving back to the farm at 23 mpg is as follows: (100/23)*2/12000 = .000725 gallons of fuel per pound of goods. For shorter distances, say 50 miles and 25 miles farm to market, the gallon per pound usage is .000363 and .000181 respectively.

Not bad. At the national average of 4.7 pounds of food consumed per person per day, a resident of Smallsville getting their food from farmers 100 miles away use .0238 gallons of fuel to get their food every week.

Now for the residents of Bigsville. The food that these residents buy is shipped to them from much farther than 100 miles. For the sake of argument lets say their food is shipped from, on average, 1,500 miles away. Yes, California oranges make their way to New York but some foods are sourced much closer than 1,500 miles. Thus, a 1,500 mile average seems to make sense for our calculations. Further, for the sake of simplicity, let us speculate that on the return trip each truck is empty. I do not know the details of the shipping industry but I would imagine that they try to avoid empty trips as much as possible. Not having these details, though, we are forced to consider the truck empty on the return trip.

Each 18 wheeler truck can carry 44,000 lbs and gets roughly 7 mpg. The gallon per pound rate that Bigsville residents consume is (1500/7)*2/44000 or .00974 gallons of fuel per pound of food. At the 4.7 pounds of food per day average, a resident of Bigsville uses .320 gallons of fuel per week for food transportation. This means that the F150 driving farmer who supplies Smallsville is using 1/13th the amount of fuel per pound of food! Much more efficient.

This isn’t the whole story though.

Personal Transportation
Because Smallsville is not a major metropolitan area, the residents use their own cars for nearly all of their transit needs. In a best case scenario, a resident of Smallsville needs to travel 10 miles per day (driving to work, driving to pick up the kids). This is a very low estimate as the national average is 29 miles per day, nearly three times as much. Because Smallsville is a small town and because its residents are careful not to use their cars, 10 miles per day seems reasonable for our calculations. 10 miles per day equates to 70 miles per week.

The average fuel efficiency for passenger vehicles in America is roughly 23 miles per gallon. At this rate, Smallsville residents are consuming 3.043 gallons of fuel per week to move themselves from place to place.

Meanwhile, the residents of Bigsville use their public subway system as cars are prohibitively expensive in the big city. Various studies have put the energy usage of these electric subway cars at 2.61 kWh/person-km. According to James Strickland, 2.61 kWh/person-km equates to roughly 8 miles per gallon. That sounds low but one must remember that the subway car is getting 8 mpg to move 315 passengers (instead of the 23 mpg to move 1 Smallsville resident in their car). At this full capacity of 315 people per subway car, the per person mpg is 2,520. Even if the subway car is moving only 66 people, all of whom would be able to have a seat, the per passenger mpg is 528.

Now, metropolitan Bigsville covers an area roughly 15 miles long and 2 miles wide. Yes, it is shockingly similar to Manhattan in this respect. A resident of Bigsville travels 40 miles per day, 4 times more than Smallsville residents and 11 miles more than the national average. They live on one end of the metropolitan area and commute to the other end 15 miles away. They do this commute twice a day for a total of 30 miles. In addition they travel 10 miles a day extra running errands. 40 miles per day means Bigsville residents travel 280 miles a week in the city. Even if they only ride subway cars that are at fifth capacity (roughly 66 riders) and walk nowhere (highly improbable considering how close they are to many destinations) they use only 1.886 gallons of fuel for transportation every week.

_Conclusion and Further Exploration_
To bring it all together: a Smallsville resident, who gets 100% of their food from local vendors and drives 10 miles per day in their average gas milage car, uses 3.0668 gallons of fuel per week or about 159.5 gallons per year.

A Bigsville resident, who gets 100% of their food from 18 wheeler-supplied groceries stores where the food travels on average 1,500 miles from farm to market, and travels 40 miles per day uses 2.206 gallons of fuel per week or roughly 115 gallons per year.

Smallsville residents use 38.7% more fuel.

Are there complicating factors? Of course. We have completely ignored other fuel uses from trash transportation to durable and nondurable good transportation to heating and cooling. Some of these would fall in favor of Smallsville residents, like trash transportation, while others would be more efficient for Bigsville residents like heating and cooling, while still others are probably a wash like durable/nondurable good transportation.

However, the upside possibilities for Bigsville residents seem to outweigh those of Smallsville residents. What if, instead of 18 wheelers, the food going to grocery stores in Bigsville was transported on trains? A train can get much higher fuel efficiency than trucks. American freight trains, on average, can move 2,000 lbs of goods 436 miles on 1 gallon of diesel fuel. If all the trucks moving things to Bigsville were replaced by trains and the same 3,000 mile round trip was required, trains would only need 151.3 gallons of diesel while trucks would need 428.6 gallons of fuel.

While trains could also be used to deliver goods to Smallsville, the efficiency benefit would not be as high due to multiple stops and a possible inability to formulate a reliably consistent delivery circuit that mimics the simplicity of the A to B circuit Bigsville trains would enjoy.

In closing: without considering the multitude of other complicating factors, it is not entirely obvious that small cities and farmer’s markets are inherently greener than big urban centers.

What about a community that is not as dense as Bigsville but more populated than Smallsville? These suburbs are the real efficiency hogs. Their problems are many: due to their layout they often require residents to drive far more, often there is not enough density to make subways or other high efficiency public transit feasible and suburbs suffer from an over choice of shopping possibilities that would make simple A to B truck or train transportation setups not possible.

Average passenger car mpg
Train fuel usage
Produce image used under CC BY-NC-SA 2.0 license. Photo by flickr user LN.


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31. March 2011 by Chris
Categories: Thought Experiments | Tags: , , , , , , | Leave a comment

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