I don't know how it is supposed to work on the Jazz, but as I mentioned all the radio stations were giving traffic alerts, and of course, Google Maps knows as it monitors all our phones, so it knows what speed we are moving at (or not).
Radio stations only get there information from the Highways Agency, or in Scotland, the police. Our local radio still reports roadworks which ended several months ago!
I assume with Google Maps you agree when you install the app for them to monitor your location.
As for GPS, lots of people think the satellite knows where you are. It doesn't. The GPS receiver knows where the satellites are, and with that information calculates where you are in relation to the satellites. The increased accuracy will only be available if your sat nav can make use of it. My old TomTom One cannot even tell if you are on a Motorway, on the slip road, or on a minor road paralleling the motorway!