, 70? I'm sure flat vs hills, slow grades vs steep all make a difference I'm just currious. Btw I've got about 70miles on gas and I'm at 40.2 
around 215ish overall mpg with somewhere around 350 miles +-20.The third graph in the post here provides some insight. Regardless of power source, efficiency drops at speeds above 55mph primarily due to air resistance.
http://gm-volt.com/forum/showthread.php?288713-Effect-of-Speed-and-Temperature-an-extrapolation-for-2017-Chevy-Volt
The Volt is most efficient between 20 and 36 mph. For overall best efficiency use EV mode for driving at all speeds until the battery charge is depleted (contrary to my example below) and then use gas. Hold mode can easily exceed the EPA mpg estimate of 42mpg combined. You want the gas engine to reach full operating temperature for best efficiency, monitor the engine coolant temperature and you will see it stabilize at between 185 and 205 F, then it has reached full operating temperature.
If you consider the cost of electricity in your area then at current gas prices EV mode and when using gas may be within 1 cent per mile of actual cost. The last time I calculated this in my area the cost was 4.5 cents per mile EV and 5.5 cents per mile gas.
I usually try and hold my highway speed to no more than 62 - 65 mph (EV) and 65 - 70 mph (gas).
On a recent trip I traveled ~70 miles (60 miles highway and the rest secondary roads): 55 miles EV and 15 miles using gas. The Volt displayed 54.7 mpg (gas) but I am sure this included additional miles due to regeneration. I used Hold mode for part of the way (both going and on the return trip) as I like to arrive home on battery power. My Volt still had approx. 4 miles of EV range when I arrived home so I could have traveled a bit further on battery than I did. The air temperature was in the 70s. The Volt showed a combined MPG of 250+
The unused battery capacity (approx 1 kwh) was not wasted, the Volt recharged in 4 hours instead of 4.5 hours it would have taken if the battery had been fully depleted. I estimate I used an additional 9 oz. of gas to travel the extra 4 miles on gas instead of battery.
http://gm-volt.com/forum/showthread.php?288713-Effect-of-Speed-and-Temperature-an-extrapolation-for-2017-Chevy-Volt
The Volt is most efficient between 20 and 36 mph. For overall best efficiency use EV mode for driving at all speeds until the battery charge is depleted (contrary to my example below) and then use gas. Hold mode can easily exceed the EPA mpg estimate of 42mpg combined. You want the gas engine to reach full operating temperature for best efficiency, monitor the engine coolant temperature and you will see it stabilize at between 185 and 205 F, then it has reached full operating temperature.
If you consider the cost of electricity in your area then at current gas prices EV mode and when using gas may be within 1 cent per mile of actual cost. The last time I calculated this in my area the cost was 4.5 cents per mile EV and 5.5 cents per mile gas.
I usually try and hold my highway speed to no more than 62 - 65 mph (EV) and 65 - 70 mph (gas).
On a recent trip I traveled ~70 miles (60 miles highway and the rest secondary roads): 55 miles EV and 15 miles using gas. The Volt displayed 54.7 mpg (gas) but I am sure this included additional miles due to regeneration. I used Hold mode for part of the way (both going and on the return trip) as I like to arrive home on battery power. My Volt still had approx. 4 miles of EV range when I arrived home so I could have traveled a bit further on battery than I did. The air temperature was in the 70s. The Volt showed a combined MPG of 250+
The unused battery capacity (approx 1 kwh) was not wasted, the Volt recharged in 4 hours instead of 4.5 hours it would have taken if the battery had been fully depleted. I estimate I used an additional 9 oz. of gas to travel the extra 4 miles on gas instead of battery.
