I am using a GS3 and changed to Google Voice Recognizer and it worked.
Settings>Language and Input>Voice Recognizer

It's not that it can't hear you, it's that it doesn't understand what you've said, the message is misleading.

Same problem here. GS3, stock Android 4.1.2. A few months ago voice commands for traffic or hazards used to work. But no more. What is frustrating though is that once I reach my destination, if I wait for a bit and fire up waze again, and "test" a voice commanded hazard, it hears me just fine. It's only when I'm underway it doesn't work. A fix here would be HUGE, because as mentioned by others, feeding back this sort of road intel to the community via screen taps is way to dangerous. The voice idea and menu structure I think was well thought out (when it worked for me way back when anyway). But now I am no longer able to contribute feedback to the community.

Slates89 wrote:I fixed my Samsung S3 using stock 4.1.2 rom by changing to Google for TTS rather than Samsung TTS. Hope this helps.

I've been using Google TTS and not the Samsung TTS, and still have this issue. Not sure what is going on.