This is an attempt to answer my own question. This what I perceive but it may not be true. I wish someone could verify or invalidate this anecdotal observation of mine.
I was driving across the whole stretch of I-80 in Nebraska. Relatively flat terrain with some infrequent undulations. Ideal for hypermiling. The speed limit was 75 but I was driving at 55 mph. And the gas prices were $3.299.
But I managed only to attain 40 mpg across Nebraska. In fact, it did not make any difference whether I drove at 40 mph or 60 mph. It was still 40 mpg. Though driving at 75 mph dropped it down to 30 mpg.
The Honda Civic/Accord has a sticky gas pedal, someone told me. When you depress the gas pedal it will reach a point of impedance to your foot pressure. After which, you would have to press harder to inject more fuel into the engine.
Here was my experiment:
When I depress the gas pedal until the point of stickiness, I have anecdotal observation from the sound of the engine, that the engine is still idling at minimum fuel intake.
Until my recent long distance drive, I had tried depressing the clutch to avoid engine drag to allow me to cruise at 40 mph. Which does get me 40 - 42 mpg.
However, just for the past week, I decided to try never to disengage the clutch but to cruise on the 4th gear with the gas pedal depressed to the point of stickiness. There is some magic going on with the Honda sticky gas pedal. After 300 miles of driving that way over the past week, mostly cruising between 40 - 60 mph, I am getting 55 mpg. And, I was not revving up to 60 mph to cruise down to 40 mph. I was driving at constant speed depending on the speed limit of the road.
I am getting 55 mpg, without performing weird tricks like cruising to the traffic lights at 5 mph. I merely ensured I do not accelerate too quickly and kept a 500 ft separation from the car in front of me. Of course, Colorado drivers were showing their anger at me by deliberately zipping past me with their truck engine revved up or beeping at me for traveling at 50 mph on a 45 mph speed limit. I find it difficult to understand why they race to the red light at 40-50 mph to wait for it to turn green when you could cruise there? Nobody does that to you in the Puget sound peninsula.
My theory is, the sticky point on the Honda gas pedal is somehow connected to freeing the clutch to allow the car to cruise without being dragged down by an idling engine. If that is true, Honda is brilliant.
If not, what else explanation could there be for my having achieved 55 mpg, cruising 40-60 mph without needing to step on my clutch? The point is - if I lifted my foot off the gas pedal completely, engine drag would slow the car down to 30 mph. So Honda's sticky gas pedal is a brilliant piece of engineering that I do not understand. And my car is not even a hybrid.
Perhaps, Honda has already done what I asked in this question and I had not been aware of it.