> Don’t you agree?

No, not in the U.S., for ~99% of cases. When traffic is moving at 5 to 10MPH over the limit (hardly rare, in my area), everyone driving on the road knows knows that they're surrounded by speeding cars. Beyond that - the police certainly know about speeding, and don't make it a priority. And the legal, easily-faked-evidence, and DWB issues with speed camera apps on Pat Smith's cellphone would be extra-bonus messes for an already-low-priority crime.

I'm not sure how this would help in the long term. As it stands, most people ignore those flashing signs that tell you to slow down, or immediately speed back up once they pass the sign. Two ways we can really reduce speeding in the long term are better street design and building cities that don't require the use of a car. Mediumly-dense, mixed-use development means people can live close to where they work and shop and won't require cars. Better street design means a lot of things, but essentially it boils down to more tree-lined streets and narrower lanes. When lanes are wide and there Are no obstacles, drivers feel safer to blow past the speed limit, as opposed to when roads are narrower and there's a constant, looming threat of running into a tree trunk or bollard if they go too fast.

It’s not a solution even slightly close to the proper ones you mentioned for sure. It might just give visibility to the problem and prove how common ignoring speed limits is. It’s a stretch but if drivers feel anyone with a phone can see they are irresponsible drivers might change their behavior.

This assumes that speeding is what takes lives. As long as everyone is going the same speed, things are relatively safe. I don't think more laws are the solution that we should look for, or that ignorance is the cause.

Honestly, in the U.S. we should be raising speed limits.

Multiple sources say speeding is the main cause. One source disagrees: drivers who love speed :D

As they say "Kill the cop in your head".