Just being on a public road in an area that is under contruction does not given police sufficient reason to pull you over
Police officers certainly have a duty to protect the public as a whole. Part of this duty would be to protect areas under construction from thievery. However, just because you are driving on a public road out of one of these areas is not by itself sufficient reasonable suspicion for a law enforcement officer to stop your vehicle, even if it can be one factor out of several to establish articulable suspicion.
Illegal stop by police = Evidence arising from the stop cannot be used against you
If the stop was unlawful, then any other evidence arising from the stop (such as evidence of driving under the influence of alcohol) cannot be held against you. You or your attorney should file a motion to suppress to have the evidence against you excluded. Without the evidence, it will be very hard for the prosecution to pursue it's case against you.