Many police officers are very professional and work hard to perform their job well. But, in the real world, some are better than others. When a driver is stopped in Chattanooga on suspicion of driving under the influence of alcohol, the officer can carefully note the condition of the driver, their behavior, their competency in performing field sobriety tests, and anything else of relevance that would support an assertion of a DUI charge. This demands experience and skill and in a trial, may require a significant amount of time from the officer to prepare.
Or, they take a breath test reading and present a blood alcohol content (BAC) number to the jury. After all, with the definition of DUI in Tennessee being a BAC reading of greater than 0.08, obtaining that number from something like a breath test is all it takes to show that a motorist is guilty.
However, the value of that number is entirely dependent on a couple of factors. The test must be preformed correctly and the machine must be properly calibrated, otherwise, the numbers are meaningless. But the magic box producing magic numbers carries the appearance of scientific fact.
In Washington, D.C., the police virtually stopped making DUI arrests when their Intoximeter technician quit. The department has filed lesser charges that do not require a measurement of a driver’s BAC, but those cases are more complex because they lack the veneer of “fact” the breath test provides.
While intoxicated driving can be shown by something other than a BAC, the bottom line is that law enforcement often does not want to go to the trouble of building a case, and would rather use a magic box that creates a number that may or may not indicate intoxication.
The problems in D.C. can occur in any city and BAC readings from breath testing equipment may not be as accurate as they appear. Every DUI should be challenged in court, forcing the prosecution to prove that every test was done correctly.
Source: washingtonpost.com, “D.C. police take most breath test machines out of service,” Peter Hermann, Keith L. Alexander and Spencer S. Hsu, September 19, 2015