Q
Do I have to answer police questions?
 No.  You do not have to answer police questions during an interrogation or at any other time.  You have a right to remain silent whether you are a witness or a potential/actual defendant.  A witness can be subpoenaed and force to testify in court, if it is believed they have relevant information concerning a case.  However, the court, government, nor prosecutor can make you testify a certain way.  The court can force a witness to testify by granting the witness immunity and using the contempt power of the court.  However, a potential/actual defendant cannot be forced to testify against himself/herself due to his/her Fifth Amendment right to remain silent.  As such, a defendant does not have to answer any police questions and cannot be forced to testify in his/her own case.  Please keep in mind 
you have the right to speak with an attorney and/or have an attorney present with you prior to answering questions of the police.  However, the police can ask basic questions during a traffic stop such as your name, address, date of birth, insurance and title information for the vehicle being stopped without allowing you time to speak to an attorney.