Create a gps app that records the car speed, checks traffic and operates like any other gps app.
Once app is running their should be ZERO distraction to the user. Meaning nothing pops up on the screen, no sounds of incoming mail / text, no blinking lights of any sorts, basically rendering the phone useless for the duration of the trip.
When app is running if the home button is pressed than it will show the following message that (for your safety the phone is temp. off)