PDFJUSTICE ALITO announced the judgment of the Court
and delivered an opinion, in which THE CHIEF JUSTICE,
JUSTICE BREYER, and JUSTICE KAVANAUGH join.
In this case, we return to a topic that we have addressed
twice in recent years: the circumstances under which a
police officer may administer a warrantless blood alcohol
concentration (BAC) test to a motorist who appears to
have been driving under the influence of alcohol. We have
previously addressed what officers may do in two broad
categories of cases. First, an officer may conduct a BAC
test if the facts of a particular case bring it within the
exigent-circumstances exception to the Fourth Amendment’s general requirement of a warrant. Second, if an
officer has probable cause to arrest a motorist for drunk
driving, the officer may conduct a breath test (but not a
blood test) under the rule allowing warrantless searches of
a person incident to arrest.
Today, we consider what police officers may do in a
narrow but important category of cases: those in which the
driver is unconscious and therefore cannot be given a
breath test. In such cases, we hold, the exigentcircumstances rule almost always permits a blood test without a warrant. When a breath test is impossible,
enforcement of the drunk-driving laws depends upon the
administration of a blood test. And when a police officer
encounters an unconscious driver, it is very likely that the
driver would be taken to an emergency room and that his
blood would be drawn for diagnostic purposes even if the
police were not seeking BAC information. In addition,
police officers most frequently come upon unconscious
drivers when they report to the scene of an accident, and
under those circumstances, the officers’ many responsibilities—such as attending to other injured drivers or passengers and preventing further accidents—may be incompatible with the procedures that would be required to obtain a
warrant. Thus, when a driver is unconscious, the general
rule is that a warrant is not needed.