A Fairfax County, Virginia General District Court judge earlier this month backed away from driving under the influence of alcohol (DUI) charges filed against a motorist after a defense attorney cast doubt on the accuracy of the county's breath testing machines. Police and courts often entrust machines like the ten-year-old Intoxilyzer 5000 with the authority to exonerate or convict a motorist of serious charges that carry significant monetary penalties, loss of license and jail time. Richmond DUI attorney Bob Battle found that this particular machine, which is being phased out in Virginia, has a significant weakness.

"When I got the records of the machine, it showed that one of the motors -- it's called a chopper motor -- had been replaced," Battle explained. "I found out that Virginia bought a bunch of replacement motors from random companies and they couldn't even tell you what motor was in there... it's very important what they are, and if they measure that the Ohms that they use, the frequency, is different than the original, it's going to cause the whole contraption that is this Intoxilyzer 5000 to be inaccurate."

Electrical engineer Thomas Workman, a former quality manager for Hewlett Packard, explained the importance of this particular motor to the Intoxilyzer 5000.

"If a replacement motor rotates at a faster RPM, then the processor may not have enough time to complete all the computations it must perform each revolution of the wheel (since there are more computations that must be done, since there are more revolutions of the wheel per unit of time)," Workman wrote. "Make the motor turn slower and the problem is that the software thinks that slopes are not being met when they should be, making the mouth alcohol detector faulty."

Although the general principles behind the machine's components are well known, the software used to generate the final calculation that determines guilt or innocence is held to be a "trade secret." Manufacturer CMI Inc. has refused to disclose the source code that would allow an independent analysis of the device. The state Department of Forensic Science guidelines only recommend testing Intoxilyzer machine components with an oscilloscope -- something the state has never done.

Presented with the evidence on the motor issue, the judge in the Fairfax County case agreed to allow experts to test the breath machine for accuracy. To avoid this, the prosecutor offered to reduce the DUI charge to reckless driving allowing the accused to keep his license -- a deal too good to turn down. Battle believes one day the machine will eventually be tested.

"I sincerely believe it's going to be like that scene from the Wizard of Oz," Battle said. "Once they roll back that curtain, they're going to find that this machine is not the perfect machine they try make it out to be -- that this is an outdated contraption. That's why Virginia, when they contracted for the new replacement machines, one of the conditions was that it couldn't have this type of motor in it."

In 2007 the General Assembly appropriated $1.8 million to replace the Intoxilyzer 5000. At the time lawmakers argued that replacement was necessary because machines like the Intoxilyzer were "dated, unstable and unreliable."

View an interview of Bob Battle on the Intoxilyzer case by Ben Glass: