To the OP.

Yes, in a "Plug-In" Ford Escape ( I've driven one for 4 days ) battery assist occurs at all speeds. You can get extended periods of EV if you are going slow. This is true.

On the Highway, you will get up to 90 MPG for the first 25 miles, then regular MPG after that.

With a mix of EV and ICE use in the city, I net 141 MPG during 5 HOURS of driving.

-John