I think the popups are great in WAZE but, if you are approaching an accident and it asks you to select thanks or not there, it can cause yet another accident.
What I propose is a voice prompt.
When you get to 0m/ft away from the report, it asks you if it's still there "Yes/No". If you reply Yes, you automatically say thanks and if it's not there, it removes it from the map.
The voice recognition will be simple and only contain a few words:
"Report Major Accident"
This would allow users to keep their eyes on the road and promote road safety.