Why should cell phones be banned while driving a vehicle?

It helps to have one with you in case of emergency because you can call 911 on it, but I think that people should not be allowed to use them while driving unless they are in an emergency situation while driving, such as a car that won't stop because the brakes won't work, or trying to flee from an earthquake that has affected the road they are on, or something like that. no matter were u are you need a cell phone you might be aducted and you dont have a cell phone to call for help now do you?so go to target whaile you still can and get a pay as you go and the tracfone and be save for crying out loud!!