I was just on the highway this afternoon with my PHEV and once I reached 110 km/h, the vehicle did switch to EV only mode. As long I was able to stay at 110 km/h it stayed in EV mode for the time I was on the highway. For the most part it tries to stay in EV mode if that is what you selected for the mode. I have so far been able to spend the majority of my driving mostly highway in EV mode.