It is usually best to pull over when calling 911, as there is less chance of the cell phone signal being dropped if in a stationary location. Additionally, any emergency instructions that need to be carried out can best be done while stopped. Finally, if help needs to reach you it is best to be in one place so help can get to you, instead of trying to meet them somewhere. If you cannot safely pull over to speak to 911 then stay calm, pay attention to the roadway with surrounding vehicles, and follow the 911 call taker's instructions.