Thank you so much. that's o helpfulYou can add your own speed cameras to a Nuvi using Point Of Interest (POI) files, these can be displayed on-screen and also play an audio alert when approached, have a look at the link here :-
https://www.gps-forums.com/threads/how-do-i-load-pois.46547/
The *.GPI can be generated by the Garmin POI Loader program detailed in the link above