You forget that the Bolt EV uses no gas, so its MPG would be infinite, still beating out the Volt in this category.
However, the Bolt EV can't drive long distances easily. I put approximately 9k electric miles per year on the Volt, maybe 1,000 mixed gas/electric miles during winter, and 2,000 gas miles due to long trips. The Bolt EV would eliminate the 1,000 mixed winter miles, and maybe 300 of the longer range miles, but I would still have to put around 1,700 miles a year on a gas vehicle. Flying is not an option for this, so it means the minivan that gets around 22 mpg on the highway. It isn't a huge amount, but maybe means 25 gallons of wasted fuel, but the Bolt would save that back from not having ERDTT/longer winter range than Volt. My net fuel use would be a wash, maybe save a few gallons a year.
However, if my wife also switched to a PHEV Chrysler Pacifica, she drives up to 20k miles a year. I estimate she could save 10,000 gas miles a year, mostly poor MPG city miles, so 17 mpg, and that would reduce my fuel usage by about 600 gallons per year only considering EV miles, it is also a more efficient van, so that might reduce it another 60 gallons.
My point is I can save far more fuel buying PHEV than a BEV, and this will be true for many US families. I understand that on an Island or small area the BEV makes far more sense.
