I guess there are some reasons why bus drivers are not allowed to discuss with the passengers in many countries.

according to John Medina's book [Brain Rules], rule number 4 (attention) he says "Driving while talking on a cell phone is like driving drunk. The brain is a sequential processor and large fractions of a second are consumed every time the brain switches tasks. This is why cell-phone talkers are a half-second slower to hit the brakes and get in more wrecks." so maybe that is true for lighting a cigarette or putting it down. or actually playing with the setreo to change a CD or a tape