I work on a navy base where the speed limit is 15 to 35 miles per hour (strictly enforced). That's the last 1.3 miles of my commute. The 3 miles before that is 35 - 45 miles per hour. I used to try and get the car to run in EV mode as much as possible during that time by doing about 40 in the 45 zone when no one was in back of me. Problem is that the the battery level would drop too low during the last part of the trip and I was running on the ICE doing 15 miles per hour on base.

At 45 - 55 miles per hour while running on the ICE I'm getting over 30 mpg. At 15 - 25 miles per hour I'm getting 15 - 20 mpg. I found that I was better off running in EV mode in the 35 miles per hour zones and putting the speed to 53 miles per hour in the 45 zone. That keeps me below the ticket threshold, the car runs more efficiently at 53 than 45 and when I arrive on the base I have a full charge on the battery.

Moral of the story. Save the battery for when you'll get the most benefit.