The next time your coasting in drive with the ice is off and the battery is charging. Slip the lever from drive to neutral. You will be gliding. If you need any braking, be sure to move it back to drive then brake. I do this when i'm coasting down some mountains that are not too steep. I leave it in drive on the steep ones.

Someday I will measure the angles of the two mountains I do this on. Actually I did not pick up as much mpg as I thought I would gliding the 15 miles in neutral. Next time I will try it in drive for comparison.

My theory. The reason the TCH don't glide in drive, is that is has only one generator/motor. It switches electrically in a instant to charge the battery or drive the wheels.

The Prius has two separate motors, one generator and one drive motor. They may use a relay to do the switching from one to the other. Could be the ECU is programmed to have the glide function.