Do You Know How Many Miles You Drive?

The Center for Transportation Analysis of the Oak Ridge National Laboratory has a publication called the Transportation Energy Data Book. In it you can find all sorts of interesting data. There is a section called Self-Reported vs.Odometer Average Annual Miles available as a Microsoft Excel spreadsheet. One fundamental principle of saving on gas is that you have to know how much you are using to know if you are saving or not. You have to know how much gas you are putting in your tank how often and how many miles you are driving in between fills. Getting into the habit of watching these things is important. Otherwise it is all too easy to forget everything except for the last fill up. That can convince you of things that are not true.

For example, maybe you tried a new hypermiling technique for a couple of days. Then you went to the pump and were surprised at how much money the bill was. You conclude the technique did't work. But what you might not be aware of is that you actually drove quite a few more miles before that fill. Or maybe traffic was especially bad. You have to keep a long term watch over what is going on.

Anyway, the interesting thing about the self reporting odometer study done by Oak Ridge is that on average people do not know how far they drive in a year. I have reproduced the data from the study here.

Self-Reported vs. Odometer Average Annual Miles, 1995 NPTS and 2001 NHTS

Vehicle age (years)	1995 self-reported	1995 odometer	2001 self-reported	2001 odometer
Under 1	15,900	15,600	15,500	14,500
1	16,800	14,500	14,300	14,200
2	15,500	14,800	14,000	13,700
3	14,400	13,800	13,100	14,100
4	14,100	12,900	12,500	13,400
5	13,500	12,700	12,000	12,900
6	13,200	12,400	11,800	12,400
7	12,800	11,600	11,600	12,100
8	12,200	11,300	10,900	11,300
9	12,200	11,200	10,800	10,500
10 and older	8,900	9,000	7,400	8,100
All household vehicles	12,200	11,800	11,000	11,800

The study was done twice, once in 1995 and again in 2001. Both times Americans said they traveled an annual distance that the odometer disagreed with. One observation is that in the years between the studies, the error switched sides. In 1995 Americans thought they drove more than they actually had. This conservative estimate would help to reduce gas usage and let families build a little safety into their financial planning. But in 2001 Americans thought they had driven less than they really did. This is a worrying trend. Underestimating your driving is likely to discourage efforts to save on gas. It also throws off family budgeting because it will generate unexpected shortfalls. Kind of like the "all risk" style of modern banking.