“Be kind, for everyone you meet is fighting a hard battle” - Often attributed to Plato but likely from Ian McLaren (pseudonym of Reverend John Watson)

Wednesday, June 07, 2006

The curve

I've been playing with the numbers from my fuel consumption generated over the last 275 days. It appears there is strong evidence of a learning curve on fuel minimizing driving techniques. I placed the numbers for my fuel consumption in a post a couple of weeks back. Since then I've filled up twice.

I graphed the miles per gallon for each fill up and the five tank moving average of mileage at fill up. I then had Excel calculate a linear regression for each data set. The linear least-squares line for the per fill up data is y=0.1008x+20.251 and for the five tank moving average it's y=0.0777x+20.845 where y is the miles per gallon and x is the "fill-up number."

Obviously, the 20.251 and 20.845 (the "y intercepts") can be interpreted as the mileage I was achieving at the outset of the experiment. The 0.1008 and the 0.0777 (the "slopes") can be interpreted as my average increase in miles per gallon achieved per tank full, in other words, my learning to minimize fuel consumption.

The majority of my mileage is on my commute which has not changed and there hasn't been any significant change to the remainder of the vehicle usage, so I think these positive slopes really do represent my increasing ability to drive in a maximally fuel-efficient manner.

The fact that my last four fill ups have resulted in the five tank moving average being above the trend line indicates that my learning is still in progress. Clearly this will have to come to a halt, since otherwise in five years I could expect to be getting 46 miles per gallon. I somehow doubt that that will occur. But I will be very interested in seeing what the number looks like when the learning curve levels off.

On another note, I achieved a milestone (pun intended) today when the average mileage reading on the display clicked to 23.0. Starting from 14.9, I'm amazed. I'm not sure if 24 miles per gallon on the display is in the cards, the current five tank moving average is 23.88. But I'll be trying. Right now it seems to take a couple of weeks or so to goose the display up by a tenth of a gallon, so if I can make it to 24 it will take at least something over four months. I should have been keeping a log of dates that the display changed.

Oh well, I can't think of everything.

1 comment:

Bill Anderson said...

I would be leery of putting too much stock in the results to date. Gasoline is formulated differently between winter and summer (known as blends). Once you've got a year over comparison you can compare similar blends of gasoline and thus the data would be much more accurate. Also interesting would be your choice of gasoline source. Despite public claims to the contrary, I have established in personal experience that there is indeed a fuel economy difference between various supply sources. In some cases 10-18% difference. Just a thought.