Document ID: ./input/supremecourt_opinions/opinions/12pdf/11-1425_cb8e.pdf
Page Number: 34.0

Cite as:  569 U. S. ____ (2013) 

5 

Opinion of ROBERTS, C. J. 

tional  penalties  for  drivers  who  drive  with  a  “high  BAC,” 
often  defined  as  0.15  percent  or  above.    NHTSA,  Digest
of Impaired Driving and Selected Beverage Control Laws, 
pp.  vii,  x–xviii  (No.  811673,  Oct.  2012).    BAC  evidence 
clearly  matters.  And  when  drivers  refuse  breathalyzers,
as  McNeely  did  here,  a  blood  draw  becomes  necessary  to
obtain that evidence. 

The  need  to  prevent  the  imminent  destruction  of  BAC 
evidence  is  no  less  compelling  because  the  incriminating 
alcohol  dissipates  over  a  limited  period  of  time,  rather 
than  all  at  once.    As  noted,  the  concentration  of  alcohol 
can  make  a  difference  not  only  between  guilt  and  inno-
cence,  but  between  different  crimes  and  different  degrees
of  punishment.    The  officer  is  unlikely  to  know  precisely 
when  the  suspect  consumed  alcohol  or  how  much;  all  he 
knows is that critical evidence is being steadily lost.  Fire 
can  spread  gradually,  but  that  does  not  lessen  the  need 
and  right  of  the  officers  to  respond  immediately.    See 
Tyler, supra. 

McNeely contends that there is no compelling need for a 
warrantless  blood  draw,  because  if  there  is  some  alcohol 
left  in  the  blood  by  the  time  a  warrant  is  obtained,  the 
State  can  use  math  and  science  to  work  backwards  and 
identify  a  defendant’s  BAC  at  the  time  he  was  driving. 
See  Brief  for  Respondent  44–46.  But  that’s  not  good 
enough.  We  have  indicated  that  exigent  circumstances 
justify  warrantless  entry  when  drugs  are  about  to  be 
flushed down the toilet.  See, e.g., King, 563 U. S., at ___– 
___ (slip op., at 7–8).  We have not said that, because there 
could  well  be  drug  paraphernalia  elsewhere  in  the  home, 
or  because  a  defendant’s  co-conspirator  might  testify  to 
the  amount  of  drugs  involved,  the  drugs  themselves  are 
not crucial and there is no compelling need for warrantless 
entry. 

The  same  approach  should  govern  here.    There  is  a