The issue is that the local Police are aggregating the same types of data E.G. Auto scanning tags of cars within sight of a police car and it's only a matter of time before the links are made to pool the data. All that needs to happen for this to become a reality is one piece of legislation be snuck into a spending bill or farm bill etc.. and bam - all police forces are required to send their data to the national data pool that all other police forces can access for the "greater good".

Not being involved in this myself I don't know the extent or the checks in place but police do have access to cell phone location data since about ten years ago? (if you call 911 on a cell phone they use it to find you)