Transmission B Mode -- Do my brake lights come on?

Observations

Artnc you were correct, this version of the Prius does not default to D after it has been in B for a certain time or distance. I drove about 20 miles in B yesterday at 60 to 70 MPH and it never came out of B. Driving at a steady speed or accelerating the only difference I could detect between D and B is that the CC can't be set in B.

But when you take your foot off the gas pedal the difference is obvious. In D or B on a particular stretch of fairly level road the tach read about 2200 at a steady 70 MPH. When I let off the gas in D the RPM dropped to a little below 1000 and there was no detectable engine noise. At the same speed in B when I let off the gas the RPM increased to about 3800 and I could hear the engine acting as an air compressor as described above.

I remember last summer coming down a long steep hill in the Rocky Mountains I had a full battery so I put it in B and didn't apply any additional braking. At 85 MPH or so I noticed the tach and it was up to about 4800 RPM, the engine noise was quite noticeable.

As far as I can tell driving in B mode doesn't really hurt anything but it is wasteful except in special circumstances.