The Constitution of the United States pretty clearly says that police can’t just stop someone and conduct an investigation unless there are “articulable facts” indicating possible criminal activity. So how can they do exactly that with DUI roadblocks?Good question. And it was raised in the case of Michigan v. Sitz (496 U.S. 444), in which the U.S. Supreme Court reviewed a decision of the Michigan Supreme Court striking down drunk driving roadblocks as unconstitutional. In a 6-3 decision, the Court reversed the Michigan court, holding that roadblocks were consitutionally permissible. Chief Justice Rehnquist began his majority opinion by admitting that DUI roadblocks (aka “sobriety checkpoints”) do, in fact, constitute a “seizure” within the language of the 4th Amendment. In other words, yes, it’s a blatant violation of the Constitution. However….

However, it’s only a little one, and there’s all this “carnage” on the highways MADD tells us we’ve got to do something about. The “minimal intrusion on individual liberties”, he wrote, must be “weighed” against the need for and effectiveness of roadblocks. In other words, the ends justify the (illegal) means….aka, “the DUI exception to the Constitution”.

The dissenting justices pointed out that the Constitution doesn’t make exceptions: The sole question is whether the police had probable cause to stop the individual driver. As Justice Brennan wrote, “That stopping every car might make it easier to prevent drunken driving…is an insufficient justification for abandoning the requirement of individualized suspicion.” Brennan concluded by noting that “The most disturbing aspect of the Court’s decision today is that it appears to give no weight to the citizen’s interest in freedom from suspicionless investigatory seizures”.

Rehnquist’s justification for ignoring the Constitution rested on the assumption that DUI roadblocks were “necessary” and “effective”. Are they? As Justice Stevens wrote in his own dissenting opinion, the Michigan court had already reviewed the statistics on DUI sobriety checkpoints/roadblocks: “The findings of the trial court, based on an extensive record and affirmed by the Michigan Court of Appeals, indicate that the net effect of sobriety checkpoints on traffic safety is infinitesimal and possibly negative”.

p.s. The case was sent back to the Michigan Supreme Court to change its decision accordingly. But the Michigan Supreme Court sidestepped Rehnquist by holding that DUI checkpoints, if permissible under the U.S. Constitution, were not permissible under the Michigan State Constitution, and ruled again in favor of the defendant — in effect saying to Rehnquist, “If you won’t protect our citizens, we will”. The State of Washington has since followed Michigan.

So what did I mean in my earlier post by "unreliable breath machines" and "passing laws against science"? Here’s just one of many examples… The computers inside Breathalyzers actually multiply the amount of alcohol in a DUI suspect’s breath sample 2100 times to get the blood alcohol concentration ("BAC"). This is because it is programmed to assume that the suspect has 2100 units of alcohol in his blood for every unit of alcohol in his breath. This is called the "partition ratio". But this ratio is only an average: actual ratios vary from as low as 900:1 to as high as 3500:1; if individual ratio is different, the BAC result will be different.

Translation: If a suspect has a true BAC of .06% ("not guilty") and a partition ratio of 1300:1, for example, the machine will give a result of .10% ("guilty"). Convicted by a machine. His crime? He was not average.

Well, when juries hear this kind of evidence, they tend to return "not guilty" verdicts. This did not sit well with MADD’s and prosecutors’ lobbyists. The result: in California and other states, drunk driving laws were changed by adding "Percent, by weight, of alcohol in a person’s blood is based upon grams of alcohol per 210 liters of breath". In other words, the law no longer cared what the actual amount of alcohol was in your blood: it was legally (not scientifically) presumed to be 2100 times what is in your breath — even though we know it is not.

The conservative California Supreme Court later found the new DUI law constitutional in People v. Bransford. But a dissenting Justice pointed out the obvious: "The majority…has on its own created the new crime of driving with alcohol in one’s breath". (Justice Joyce Kennard, 8 Cal.4th 894)

Result: today, defense attorneys are prohibited from mentioning anything about partition ratios to a jury. Scientific truth has been banned from the courtroom. And the conviction rate in drunk driving cases has risen dramatically.