The ordinary rules don't apply for DWI

A ruling by Louisiana's 2nd Court of Appeals has expanded the arrest power of police officers outside their jurisdictions. Prior to the court's ruling, an officer outside his jurisdiction was considered a civilian and could only make a "citizen's arrest" for a felony.

A private person may make an arrest when the person arrested has committed a felony, whether in or out of his presence. - Art. 214, Louisiana Code of Criminal Procedure

At trial, in two separate cases, police officers outside their jurisdiction stopped motorists they believed were driving while intoxicated. In one case, State v. Stapa, an officer noticed a motorist weaving between the fog line and the center line and called a state trooper. The state trooper told the officer to "light up" the motorist but to stay in her car until he arrived. In the other case, State v. Williams,  an officer observed the motorist driving and stopped him.

In both cases the Court acknowledged that the officers did not have the authority to make the stops -- in fact, the trial courts, in both cases, suppressed all evidence attained as a result of the illegal stops. The Louisiana court quoted from a dissent by Chief Justice Roberts to a denial of ceriorari in which Roberts wrote that "[t]he imminence of the danger posed by drunk drivers exceeds that at issue in other types of cases."

The Chief Justice and Justice Scalia went on to write:

"Drunk driving is always dangerous, as it is occurring. This Court has in fact recognized that the dangers posed by drunk drivers are unique, frequently upholding anti-drunk-driving policies that might be constitutionally problematic in other, less exigent circumstances." Virginia v. Harris, 130 S.Ct. 10 (2009).

So there you have it. The Chief Justice of the Supreme Court and "Mr. Original Intent" think that your constitutional protections are situational and shouldn't apply equally in all cases. In the two Louisiana cases, the Louisiana Court also expressed its belief that statutes protecting citizens from overzealous law enforcement don't always mean what they purport to mean (keeping in mind that Louisiana is not a common law state).