Driver Safer with Do Not Disturb While Driving
Tucked into the Do Not Disturb Settings is an option to enable Do Not Disturb while driving. This will prevent calls and texts from interrupting you, while still allowing favorites or urgent messages to get through.
Go to Settings -> Do Not Disturb and then scroll down to the Do Not Disturb While Driving option. You can set this to activate automatically based on speed and movement, when connected to car bluetooth or manually.
You can tell the feature that you are a passenger if it activates when you aren't driving. Here's more on how to set up Do Not Disturb While Driving in iOS 11.