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Originally Posted by JRMichler
What is the distance and elevation change on your commute? I see that the constant is exactly the same in both cases, 24.7. This implies that the elevation change is not affecting your mileage.
You could run another set of correlations by lumping all data together, with a to/from work variable. I use 1 for to work, and 0 for from work. The resulting coefficient is a direct measure of the effect of direction / elevation change / how tired you are / traffic variables / other confounders.
I regularly drive a route of about 60 miles with net elevation change of 800 feet. In the summer, I normally get 30 to 35 MPG uphill and 35 to 42 MPG downhill. The exact MPG depends on wind and temperature.
I also drive a 4 mile stretch of winding gravel road with 35 foot total elevation change. In the summer, I average about 38 MPG downhill and about 30 MPG uphill.
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My elevation change is only 140 ft over 25 miles. Morning commute is left to right:
I tried to the regressions with morning and evening all together, but I couldn't get anything that would get the average error under +/- 10%.
I've wondered why I do better in the mornings for a long time. I haven't figured out all of it but I think it's a number of small factors. I'm sure the elevation change does make some difference. Also, I plug in the heaters in the morning, but evenings are true cold starts. Also, even though the route is "the same", it's not truly the same. For example, if you have a red light on a hill, it's completely different if you're approaching it from the uphill side vs. the downhill side. Also, there's several right hand turns on the way to work which are left hand turns on the way home--typically it's easier to roll through right hand turns without brakes because you only have to watch one lane of traffic. Also, in the mornings I have less city/neighborhood driving before I get to the highway than I do in the evenings. Also, there's usually heavier traffic in the evenings as everybody's leaving work near the same time--that can lead to less hypermiling flexibility.