I just found out that the Volt does not exactly have a direct drive with only a reduction gear. It has a planetary gear. So in essence what this does is it works like having a 2nd gear or overdrive gear. When you go 70+ mph, the second electric motor turns on and also lowers the rpm (the Volt has 2 electric motors & 1 gas motor). This may or may not be an over simplification, but for the driver, this is all you need to know, that the overdrive kicks in at 70 mph.
As a driver you do not hear anything or feel anything going on below or above 70 mph. Although, once I discovered this was happening, since I was aware of it, I listened for it. I do not know if it is just me, but I swear I can just feel a sensation that the engine just relaxes when going over 70 mph. I feel like I can just cruise 75 mph all day long with no stress whatsoever.
I decided to run an efficiency test driving 73 mph +/- 2 mph. Well, it was using 1 kwh for 3.8 miles. That puts the range at 39 to 40 miles. It is not exactly the most efficient way to drive. If I were driving across country and had the gas engine running, I would cruise 70+ mph all the way if the hwy allowed.
If you are considering a Volt, it is nice to know you don’t have to baby the car on long trips on the hwy. It will cruise happily and relaxed 70+ mph as good or better than any car.