You should use DriveWorkout while driving in the car .
The choice is yours. You can challenge your friends or casual users of the app ; Alternative you can do training .
While driving a vocal coach will give you valuable tips and a percentage value will indicate how virtuous is your guide . No distractions for you because the background color will tell you your progress.
At the end of each training and challenge you can double check your progress and re-read the suggestions received.