This app would have four main aspects:
1. Sat nav
Pretty standard functionality but essential for getting users to put their phone into windscreen holder and open the app.
2. Looped video recording
Lots of drivers are using in-car cameras to record what’s going on in front of them so they’ll have evidence if they have an accident. This app would make use of the phone’s camera to record short videos that loop so erasing the previous recording unless you press a button to save the video.
3. Braking distance warning
Since the app is already using the camera and the GPS it could also use both to detect the vehicle in front, measure the distance between the two, and calculate the stopping distance at that speed. It would then alert the driver if they are getting too close and not leaving themselves enough safe braking distance.
4. Driving efficiency reports
Since the app is collecting data about the driving it may as well show the driver with a simple dashboard with things like top speed, average speed, etc., and more interestingly driving efficiency by calculating all the accelerating and braking and providing a score that encourages more efficient driving next time.