62.5 mpg over 50.5 miles
This car does not cease to amaze.
After driving with Hobbit that one day on the highway, I had a much better idea of what was going with his sweet spot posts. My way home that day was mildly successful, netting me probably around 56 real mpg with the hilly ride home.
Since then, I've been able to work the 15 kW routine into regular driving, including pulsing and gliding during my commute, for really wonderful figures, in spite of hills and stoplights run amok.
That being said, really quality (60+ mpg) figures have still eluded me on the few pure highway trips I've taken. Well, this morning I had the perfect opportunity to try again. I had gone up to a friend's last night (73.8 mpg over 37 miles, thank you Hobbit for 15 kW pulsing and gliding!), and then had to drive straight to work today, a drive of about 50 miles. Rather than go for a couple hours on the backroads, I decided to man up and just take the highway.
Before we start, please keep in mind that all figures noted in this post are from a calibrated Scangauge, and are very close to the real deal.
Starting out in temps of 48°F in a car that had sat overnight, I got to the highway after about 1.5 miles of 30 mpg warmup driving. I got right up to speed of around 65 mph, then tried the 15-18 kW acceleration trick combined with warp stealth downhill. For a good deal of time. I had really wanted to stick with it all trip, but the downhills didn't seem long enough to make up for uphill burns. Even when I was accelerating at the upper end of the high-torque sweet spot, I couldn't get to a high enough speed to justify using warp stealth by the top of each hill. I'd spend most of the time accelerating.
After 16 miles of this, my mileage was creeping up, it was in the high forties, then low fifties somewhere, but the whole thing was so much effort, especially with the terrain, and the five minute mileage bars were nothing special - all over 50 mpg easily, but not much higher than 60 if at all. I'd have to drive all day like this to get the average fuel economy up into the 60s.
Now, I should mention that I don't consider this a critique of Hobbit's style (the guy has got some!), but rather of my ability to control and use it properly. As the speed limit slowed to 55 anyway, I thought I would try Super Highway Mode.
The results were immediate. Next bar near 75 mpg, next somewhere in the 60s, and so on. Another 19 miles into the trip (about 35 miles in of the 50 total miles), the mileage figures were in the upper 50s, flirting with the 60 mpg mark.
I kept on, and finally 60 was broken, and it kept trekking higher - until the 2500 RPM hills came. The last 2.6 miles were hypermiling land, but even before I got to that, the mileage was still handily over 60 mpg.
So, the next logical question is how...
I travelled largely between 50 and 55 mph, set 50 as a floor for part, then 55 for another segment to see if it would still work (it did). At a given speed, I held 14 IGN on Scangauge, or occasionally 15 IGN if I really needed it (IGN on Scangauge shows ignition timing, by the way). If my speed floor was hit, I would accelerate back up a couple miles per hour faster (or just to the top of the hill if the terrain made that choice logical) at the most efficient accelerating output possible (so 15 to 18 kW) and then flipped right back to IGN 14.
That was it.
While at IGN 14, the mileage tends to be between 60 and 85 mpg. I had always thought you would lose excessive speed this way, but it wasn't the case. Using IGN 14 you slowly accelerate on the slightest downhill or even a flat (I got up to 60 mph a couple times without trying). At IGN 15, I accelerated more quickly than I thought on flats, and if you get to your speed floor on an uphill, it would usually only take a couple seconds of an efficient burn to get sufficiently back up to speed to use IGN 14 or 15 again. Unlike the warp stealth technique, the harder burns are not long at all, but quite short to bump you up a couple mph at the most. The result was that almost all time was spent between 60 and 80 mpg.
I rarely used warp stealth this trip, though I did some, especially in the second to last five minute mileage bar you saw in the second pic above (yes, that 100 mpg bar was at 50 mph, I just knew the terrain well at that point in the trip and could exploit it) and on longer downhills where I wouldn't lose much if any momentum. It was probably the most I've ever used the engine in a trip - I kept gas burning almost the entire time.
-I realize not everyone has a wide highway with Sunday morning traffic where they can go 50-55 mph. That being said, 55 mph is the speed limit in many places, and this would conceivably work at 60 mph, though with reduced efficiency, which would be perfectly acceptable in my area, especially in the right lane.
-If I take out my warmup of 1.5 miles at about 30 mpg (0.05 gallons) and the last 2.6 miles of hypermiling off the highway at 75 mpg (0.03466 gallons) from the 50.5 mile trip that used 0.808 gallons of fuel, I get a 46.4 mile trip using .7233 gallons of fuel, or slightly above 64 mpg for average highway cruising mpg throughout the trip - and that was with hills. Anyone driving on flat ground could definitely coax their Prius into better results.
-This was an astoundingly refreshing, stress-free way to drive. I absolutely love hypermiling, but it typically involves a corresponding hyperawareness of everything around you, both within the engine and without the car. Personally I'm constantly looking ahead and in every mirror to make sure I don't block a stream of traffic with a glide. It's always constant motion and thought. With highway driving at IGN 14, all you do is keep it at that one metric. That's it. If you want to go faster you go into familiar 15 kW territory for a several seconds, then back to normal. The speed fluctuations are very minimal, so if you're already in the right lane, you don't have many people flying up on your tail. You're just driving. Easy. Even if I could get the hang of Hobbit's technique, I think I would choose this one for the simplicity and relaxation I got out of it. I absolutely loved it.
-If you go onto the highway for 6 miles a day, don't expect to have a 60 mpg average. My average started low during the trip and worked it's way up gradually like I mentioned. This technique would work wonderfully on long road trips.
I don't think I've left anything out, it really was that simple. I was absolutely ecstatic to have beaten 60 mpg on the highway. Think about this: with the adjusted highway estimate for the 2007 Prius being 45 mpg, a result of 62.5 mpg with SHM at 14 IGN is 40% better than the EPA! Please ask any questions if you have them, and let me know if you're able to achieve good results on longer highway trips.