what r the chances of having a dui thrown out at preliminary hearing

The Preliminary Hearing has the lowest burden of proof that the Commonwealth has to face in a criminal proceeding.  Its important to note that this burden is so low because its not a guilt finding phase its merely a factual hearing to determine whether significant evidence exists to establish that a crime may have been committed and that you may have been the one who has committed it.  As such, it is rare to have a case dismissed outright at the preliminary hearing.  This does not mean its impossible, but because it is not a guilt finding phase the Commonwealth can refile the charges against you even if the charges are dismissed.  OFten times the best use of a preliminary hearing is to examine the officer to determine whether suppression defenses may exist.   It sounds like you have representation at the preliminary hearing.  This is wise.  A good DUI attorney can learn alot about a case at a preliminary hearing and can help you prepare for a trial.