The Supreme Court, in Missouri v. McNeely, ruled that blood tests in DUI investigations require warrants. The court held specifically that, in drunk-driving investigations, the natural dissipation of alcohol in the bloodstream does not constitute an exigency in every case sufficient to justify conducting a blood test without a warrant.
You can read the entire decision here: Missouri v. McNeely Opinion.
The impact of this decision on DUI prosecution is yet to be seen. However, this decision will likely serve to protect the rights of drivers in DUI prosecutions under the 4th Amendment. The right to privacy in one’s person is strengthened by this decision. It will prevent police from using subjective judgment before ordering invasive blood draws, prevent innocent prosecutions and vindicate those wrongly accused. Furthermore, requiring a warrant ensures that probable cause exists to prosecute in the first place.
Minnesota attorney Charles Ramsay explains:
A healthy respect for everyone’s privacy does nothing to prevent law enforcement from doing their jobs – instead, it ensures that fewer innocent people will be subjected to intrusive searches on the whim of police officers. Hundreds of DWIs may be thrown out of court as a result of this decision, but in the long term, the legal system will be further strengthened and we will see less examples of “rogue” cops who would like to act with as little judicial oversight as possible.
The warrant requirement not only protects innocent individuals from being prosecuted, but will also save the state costly litigation. It will not serve to make the roads a dangerous place but instead will ensure that proper protocols, inherent in the 4th Amendment, are followed to ensure a balance between safety and individual rights.