Work together with similar applications that use their own databases but on a nationally limited level. For example Blitzer de in Germany, Flitsmeister in the Netherlands etc. That would mean an advantage in regards of database size for both parties involved.

Make a cooperative server where Waze and other services upload data. Prevent doubled data by checking if the same kind of report already exists in a radius.

Maybe make an agreement that every service charges their users a specified amount of money for using that shared database to cover the costs of development and servers and to financially compensate the services that have the biggest share of data added to the database.