We have similar alerts in the UK from TrafficMaster and Elgin, but as yet don't have a way to remove them. If you see then while driving, pressing 'Not there' is supposed to send s signal to Waze about it. Also, HQ are working on some way for editors to delete them too. "Soon"
Reach out to your local champs and ask them to put pressure on Waze...
Re: TrafficNav alerts