That's a number I can't personally provide yet as we have yet to go on any long trips that would rely
solely on the ICE for any long distance.
I did a lot of reading online and found ranges between 35-42MPG as being an expected range, with about 38MPG being average - 6.1L/100KM. Like any other car that can be lower in the extreme winter cold, and can be better with maintaining a more moderate speed during long commute. For example, a trip across Highway 7 to Ottawa (at 85/90KPH) is going to beat a trip to Ottawa via the 401 at 110-120KPH. At 90KPH people report mid 40's MPG, or ~5.2L/100KM.
Over the ICE miles we have seen so far we seem to be averaging better than 6.1L/100KM however, around 5.5-ish, but only a full tank over a long trip will tell the real story and it's been hard to calculate our ICE mileage as all of it so far has been mixed with electric as well.
City ICE MPG are reportedly better than highway ICE MPG as well, kinda the reverse of a typical ICE car. In the city, even when the battery is exhausted, the engine still benefits from regen, so every stop light you brake (regen) at you gain a bit of electric back that delays the engine from starting again, and the engine still shuts down when coasting or stopped at a light. A good example, my wife just got home from work but had to zip out almost immediately for an appointment and even though the battery showed 0KM range she still drove completely down the length of our street towards the main road without the ICE starting using just regained buffer power from regen while coming into our neighborhood.
Yes, before anyone jumps on it (cough), the "average" ICE numbers ARE about 1L/100KM more than a Prius, but more or less on par with the Honda hybrid offerings. This is why I've said several times that there is a "magic number" of kilometers where if you can't recharge, something like a Prius does start to become a better choice...however, for our application we are ahead, particularly the ~210K or so KM we drove it Saturday, Sunday, and Monday without burning a drop of gas proving such.
For something like Taxi service where you're running major miles without the ability to charge and focus on electricity vs gas, yes, a Prius wins vs the Volt. That said, that's not our use, and we are winning significantly vs any Hybrid option.
So, todays stats:
My wife's commute to Peterborough this morning (76KM, she dropped our daughter off at work at her Co-Op, so an extra 5K vs normal) was accomplished 45.6K electric and 30.7KM gas, for a total average of 2.38L/100KM.
Calculating her trip home on pure ICE, which is the closest I'm going to get to a "straight highway ICE" calculation at this point albeit over only 70KM, it calculated out to almost exactly 6.0L/100K. Still a win vs a regular Civic which averages around 7.3-7.5L/100KM, on par with a Hybrid Civic between 5.9 to 6.1L/100K (so basically a wash), and a Prius would have averaged 4.5-5.0L/100K.
Again, when compared to the Prius, she still averaged (between electric and gas) 3.8L/100KM over 155 Kilometers, which beat it.
Once she gets her charger access at work these numbers become far better yet - all the consumption figures basically go down to half.
And hey, I hear gas is going up 6 or 7c a Litre tonight. Electricity isn't.