What Drives Us

– Tony Schaefer

“That which is documented is measured.
That which is measured is improved.”

There are several attributes as to who originated that quote, whether it was ever actually spoken, or whether it’s a mash-up of multiple quotes. As important as is the origin, the impact it can have is equally so. Basically, it’s this: if you want to improve something, start documenting. However, documentation does not, in and of itself, result in improvement. That’s where the middle step comes in: the documentation must be measured and comparisons must be made. After all, sheets of detailed documentation would be meaningless if they were tucked into a binder and never reviewed.

What Do We Document?

The following is going to be a list of as many possible things as I can imagine. In no way am I saying that you must document it all or even that every item is important to you. It’s up to you, your priorities, and your gumption to decide how far you wish to take the whole thing.

Route Timing (with waypoints)

Sometimes, the speed of the drive is more important than the mileage. Or perhaps you’re interested in finding out exactly how much longer it takes to drive one route compared to another. Consider using a small notebook and a pencil to make note of when you pass certain intersections or other static waypoints.

Create a table on the sheet. Down the left, list all the waypoints. Along the top, list Mon, Tue, Wed, etc. or perhaps Day1, Day2, Day3. Whatever. The waypoints should be far enough to allow a measureable amount of time but close enough that the measurements aren’t a half-hour apart. For example, when I did this, my 50-minute commute had eight waypoints, mostly represented by stoplights, four-way stops, or important turns.

Some unexpected benefits to logging when you pass certain areas include knowing when the train comes, knowing the school bus routes, knowing when businesses let their employees out, etc. Sometimes it’s possible to identify something that had always been taken for granted but can be completely bypassed by adjusting your travel time.

The key to logging the travel is to be accurate to the time displayed on the clock in your car. From day to day, you might leave at approximately the same time but perhaps not exactly the same time. Don’t worry about that. Just record the time exactly as the clock shows it. After the trip, go back and figure out the time it took to travel each segment. Do not attempt to calculate the travel time until after the trip is complete. Driving is hard enough without performing math.

Don’t expect a good average for the segments until you’ve driven the same route for a full week. By that time, you will know very precisely exactly when you will be passing specific points in your drive based on when you started the drive.

Route Congestion versus Travel Time

If you have the liberty, consider driving your regular commute at different times to see how traffic patterns vary. We’re not talking about hours apart, here. But no doubt you’ve noticed that leaving home fifteen minutes later than usual results in completely different traffic characteristics.

Why would you do this? If you are going to be working on achieving good mileage, you might want to be surrounded by fewer cars. For example, it is harder to pulse and glide when you are creeping along in bumper-to-bumper congestion. On the other hand, you will have fewer opportunities to drive at the speed you want when the few cars on the road want to drive all-out as fast as possible.

The key is to find that time when there are enough cars on the road to keep everyone at a reasonable pace but not so many that it’s a parking lot. I’m not going to tell you that such a situation exists in your area, but it might and you might not know about it.

Trip MPG

The good news is that some newer cars display the trip mileage on their own. You simply need to write it down at the end of the drive. If you have an older hybrid, however, you might need to reset the trip odometer to get the mileage for just that trip. If you have a non-hybrid, you might not be able to calculate the trip MPG at all. I say that because – unless you have another way – the only way to manually measure consumption over distance is to start with a full tank and then top off the tank when the drive is over. Since we’re talking about single-trip calculations, the amount of fuel consumed will be miniscule.

Documenting the Trip MPG is nice, but by itself, only presents a part of the story. For example, yesterday your trip MPG was much higher than today. Why? Without other variables, it might be impossible to know. Which is why you might want to also consider documenting. . .

Trip Temperature

Anyone who has driven a hybrid for more than a couple years knows that the ambient temperature really does have an impact on mileage. On the surface, it is easy to see that when the temperature is lower, the mileage is also lower. However, a little digging will reveal that the engine block cools down faster in the cold air and ran more to keep warm; the battery was cold in the morning and wasn’t running as efficient; or perhaps you were cold and ran the heater. Likewise, a hot battery pack is not a happy battery pack and you are more inclined to run the A/C when the temperature is above 90F.

And so it is that with the combination of trip MPG and temperature, the mystery of why today’s mileage is different from yesterday’s might be settled with an examination of the role played by ambient temperature.

Tank MPG

Most hybrids and some newer conventional cars maintain an average MPG that the user can reset; many users reset it when they refill their gas tank. In this way, an average for the entire tank can be recorded. Another way to record the tank average is to divide the number of miles driven (per the odometer) by the amount of gasoline physically pumped into the tank. This can confirm the car’s calculations or prove it wrong. Some hybrid drivers have proven that even if the tank-to-tank calculations don’t match, they tend to even out over time. Which is to say, the car’s calculation and your manual calculation might differ for individual tanks but over multiple tanks, both methods return a very similar calculation.

Average Tank Temperature

This one is a little controversial. I didn’t think it would be, but clearly I was mistaken. When I recorded and posted my tank-to-tank averages, I would refer to weather.com for temperature readings. Here’s what I did: in a spreadsheet, enter all the high and low temperatures for each day during that particular tank; then average all the numbers. This is the value I entered as “average temperature for the tank.” Was I actually driving at the hottest or coldest points of the day, every day? No. What about the days I worked from home and didn’t actually drive; did I include those days in my calculations? Yes. Why? I simply didn’t care enough to be that precise. The end result was, as far as I was concerned, close enough.

How Do We Document?

This one is entirely up to you. File it under “try a lot of things and go with whichever one works best for you.

Personally, I record the tank averages. There is an added convenience to this: with every fill-up the gas station gives me a receipt. On that receipt is the exact amount of gasoline I pumped to which I add the car’s reported average MPG and the odometer’s recorded distance. The amount f gasoline simply adds into the “total amount of gasoline consumed”. The tank distance is primarily used to verify the overall odometer.

A friend keeps a small notepad and pencil in his glove box. He records all the pertinent information there. He never transfers the data and refers to the notepad when he wants to look up past tanks. Since I transfer my numbers into a spreadsheet, the gasoline receipt is temporary.

How Do We Use the Measurements?

Most people keep their documents because they simply want to know their own mileage. It surprises some people have quickly a problem can be detected simply by monitoring the mileage. For example, some people have been able to determine they get better mileage with one gas station versus another. Others have been able to identify a failing 12-volt battery through a drop in mileage. Of course, if a hybrid battery is starting to fail, overall mileage could be a forbearer.

My spreadsheet started simple but became more complicated in time. I started with:

• Date
• Tank MPG
• Tank Miles
• Refill Gallons
• Tank Ave. Temp

With these four data points, I was able to create a historical trend graphic showing tanks over time compared to the average temperature for each tank. The “Tank Miles” was only because I wanted to know how many miles I could travel on a full tank of gas.

In time, I started getting curious about other calculations such as a rolling 12-month average and the Lifetime Average MPG. With the Lifetime MPG, I can use the sum of all Refill Gallons (Total Gallons) to compare my car to any other car driven the same total distance. By using their estimated MPG, it’s easy to show how much more they spend in total fuel costs.

Here is a screen capture showing one 12-month span from August 2010 to August 2011. This format shows the raw numbers and automatically generates the chart underneath. With the temperature shaded in the background, it is amazingly easy to see the direct impact temperature has on overall mileage.

Conclusion

Whatever your intentions, without proper documentation there cannot be proper measurement and nothing will improve. Think of it this way: if you want to tell someone you get good mileage or that you drive the quickest route, or that traffic is always bunched up this time of day, be prepared for them to say, “prove it.”

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