Alternator/generator/regulator problems of the 2007 Toyota Avalon

The radio station started to fade in and out. Then the dashboard console started to shut down and displayed the letter f (for fail). Then the engine shut down while I was driving on a divided four-lane highway in the lane closest to the median. There was no time to move into the right-hand lane. There was never any battery warning light or other indication that the battery did not have enough charge to run the engine or even to power the emergency flashers. The problem was that the alternator failed. The battery didn't need replacing. Only the alternator needed replacing. I had the Toyota service department test the battery warning light and was told that the sensor was working properly. I have had no trouble with the car since the alternator was replaced. I was told that the alternator has three diodes and the failure of one or two diodes can still provide sufficient charge. Evidently eventually all three diodes failed. I wasn't told how many failed. My complaint is that I had insufficient warning that the alternator had failed. As far as I knew, the problem was in the console which I thought would not require immediate exit from the four lane highway. The lack of a proper warning means to me that I could have been stranded on an interstate expressway without a means for getting out of a high speed lane. That is a very dangerous situation and warrants an investigation into why Toyota provides no warning for an alternator failure.