I meet way too many “out of date" hazards, so this is my suggestion.
On Waze, when a driver is approaching a hazard, a dialog box should appear. In the dialog box it should read: “Hazard still here?” The driver should then have the option to press a “Yes” button or a “No” button.
There should also be a timing and a colour code system. i.e. If the “Yes” button is pressed the clock will reset to zero, the hazard icon will stay/change to red. Other drivers can then click the hazard icon and see that this hazard has just been confirmed by another Waze user a few minutes ago.
If the “No” button is pressed, the hazard icon would change to black to indicate to other Waze users that this hazard may not be present any longer. If the hazard receive say 2 or 3 “No’s” it would then be removed.
Hope you agree :)