## Monday, September 1, 2014

### Prius+Pilot versus two Accords -- household fuel efficiency.

Multi-Vehicle Household Fuel Consumption Problems

Question:  Household A has two six-cylinder Honda Accords.  Household B has a Honda Pilot and a Toyota Prius.   Both households drive 25,000 miles per year, 50 percent in each car.   The city/highway miles ratio for all cars is 2:1.  How much gasoline do the two households consume?

Summary of information needed to solve the problem:

 City HWAY Honda Accord 6 Cylinders 21 34 Honda Pilot 17 24 Toyota Prius 51 48 Household VMT 16666.7 8333.3

Answer:   Gas consumed is equal to highway miles traveled divided by epa fuel efficiency.  (gas=miles/(miles/gas))

So for each car calculate gas consumed for city and highway.

Add gas consumed for each car both city and highway.

Results are summarized below.

 Honda Accord 6 Cylinders 21 34 VMT Both Identical Accords 16666.7 8333.3 Gasoline consumed 793.7 245.1 Honda Pilot mpg 17 24 Toyota Prius mpg 51 48 VMT Pilot 8333.3 4166.7 VMT Prius 8333.3 4166.7 Gas Consumed 653.6 260.4

Add city gas consumed and highway gas consumed to get total gas consumed.  Include expenditure estimates at \$4.0 gas and calculate a household fuel efficiency statistic.

 Household Gas Gallons Gas Expenditure at \$4.00 Household Fuel efficiency Two Accords 1038.7 \$4,155 24.1 One Pilot and One Prius 914.0 \$3,656 27.4 Difference 124.7 498.9 -3.3

In this example, the household with the Prius and the Pilot consumes 124.7 fewer gallons of gas per year than the two-Accord household.   At \$4.00 gas this amounts to around \$500.   The household fuel efficiency is 3.3 mpg higher for the household with Pilot/Prius combination than for the two-accord household.

Notes:

Note One:  Calculation for city gas consumed for household with Prius and Pilot is presented below.

(8333.3/17) + (8333.3/51) should equal 653.6

Note two:  Household fuel use efficiency can be measured as actual fuel consumed for the household divided by total fuel consumed by the household.    This number could also be obtained by taking the harmonic average of city and highway fuel efficiency numbers.   A discussion of the use of harmonic averages for fuel efficiency calculations can be found at my previous post.

Three fuel efficiency averages:

Note Three:  I have also published several blogs involving fuel efficiency and pollution reduction measurement from the use of the Toyota Prius.   See the post below.

Links in the post above can lead you to other posts on economics of owning a Prius compared to the Corolla.

This post probably understates the advantages of the Pilot/Prius combination over the two-accord combination.  More on why this is the case will follow.