Generally, the issue of the applicability of the law in a DUI case is that the courts look to the law of the state in which the offense has occurred.  So it is not a "federal offense" but a state offense.  If the law of the state is ambiguous then the court will most likely look at neighboring states and how they handle the matter.  Even if by some stretch of the imagination you landed in Federal Court on the matter the Judge would most likely apply the state law to the offense.  Generally, if there is a conflict of state and federal law then the federal law will rule.  But these matters are relegated to the states to decide.  Get an attorney.