Drivers Should Be Wary of Roadside Drug Tests

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Jeffrey Johnson is a legal writer with a focus on personal injury. He has worked on personal injury and sovereign immunity litigation in addition to experience in family, estate, and criminal law. He earned a J.D. from the University of Baltimore and has worked in legal offices and non-profits in Maryland, Texas, and North Carolina. He has also earned an MFA in screenwriting from Chapman Univer...

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UPDATED: Aug 14, 2016

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Alcohol and keysDrivers who are suspected of driving under the influence of alcohol are usually asked to blow into a portable breath testing device. No similar testing device helps the police decide whether they have probable cause to arrest a driver for being under the influence of drugs. No roadside test measures the content of a drug in a driver’s blood, and even if those tests existed, there is no scientific consensus about the drug quantity needed to establish that a driver is “under the influence” of most illicit drugs.

Police who suspect a driver has used drugs usually look for evidence that the driver is carrying drugs. They may ask for consent to search the car or the driver. If they find illegal drugs, they make an arrest for drug possession, a crime that does not require proof that the driver is under the influence of the drug.

The problem is that many drugs are not easy to identify. Marijuana has a distinctive appearance and odor, and prescription narcotics in pill form can be identified by markings, but most street drugs are trickier. A piece of crack cocaine usually looks like a piece of chalk. It isn’t easy for the police to decide whether something is or isn’t a drug unless the driver confesses.

Some police agencies have relied on an inexpensive roadside drug test to provide probable cause to arrest suspects for drug possession. Unfortunately for innocent drivers, the test frequently results in false positives, leading the police to arrest drivers who have done nothing wrong.

False Positives

An investigation conducted by Pro Publica and the New York Times Magazine found that police frequently use cobalt thiocyanate to test for cocaine. The test is simple. When a sample of the suspected drug is placed in a tube with cobalt thiocyanate, the chemical should turn blue if the tested substance contains cocaine.

The test, however, is too simple. It cannot distinguish cocaine from more than eighty other compounds that also make the chemical turn blue, including acne medications and many household cleansers. Drivers who clean their dashboards with the wrong product might find themselves arrested for drug possession if the police mistake residue from the cleaner for cocaine.

A study of cocaine field tests in Las Vegas established that one-third of positive test results over a three-year period were false. In Florida, 10 percent of field tests for methamphetamine resulted in positive results when the tested substance was not a drug. Another 10 percent misidentified a different drug as methamphetamine.

More sophisticated roadside tests require officers to follow a series of steps and then to make difficult judgments about color changes. Poor lighting and weather conditions can affect the officer’s perception of the test results, as can the officer’s eagerness to make an arrest.

Police officers are not chemists and it isn’t fair to expect them to conduct chemical tests with the precision of lab analysts. At the same time, it is unfair to subject drivers to drug arrests on the basis of unreliable tests.

Drug Exonerations in Houston

The former Houston Police Crime Lab had a notorious history of shoddy practices, including the failure to conduct tests that prosecutors requested.  A reform effort resulted in the creation of an independent crime laboratory known as the Houston Forensic Science Center. Whether the reform effort has been successful is questionable. New investigations have raised concerns about the quality of the lab’s work.

As part of the reform effort, however, tests are finally being conducted on evidence that prosecutors long ago submitted for analysis. The results of tests on suspected drugs that were identified by police officers in the field are shocking.

An audit of drug convictions by the Harris County District Attorney’s Office identified 298 cases in which the arrested individual entered a guilty plea to a drug crime based on an incorrect field test result. When lab tests were finally conducted, they revealed that the tested substance was not a drug at all. Some of those convictions have been overturned while others have yet to be remedied.

The Pressure to Plead Guilty

Why do drivers plead guilty to drug possession when they know that they are innocent? Articles in the New York Times Magazine and the Houston Chronicle each cite examples of individuals who felt they had no choice. Police and prosecutors tell arrested drivers they are facing a felony possession charge that carries a lengthy prison sentence. When they are offered the chance to plead guilty to a misdemeanor or a lesser felony, even if it means serving a month or two in jail, they decide to cut their losses and take the deal.

Drivers who cannot make bail are particularly likely to make that choice, since they will get out of jail more quickly than if they would after proving their innocence in a trial that will not be held for many months. Setting cash bail for defendants accused of low-level drug crimes produces anomalous results. Guilty offenders may be credited with the time they have already served and released after pleading guilty, while innocent defendants spend a longer time behind bars as they await lab test results.

At least 100,000 people plead guilty across the nation each year to drug offenses based on roadside tests. How many of those are innocent is unknown, but the evidence suggests that there may be thousands of wrongful convictions attributable to false positives every year.

How Drivers Can Be Protected From Wrongful Arrests

Three changes in public policy would go far to preventing wrongful drug convictions. One is to ban unreliable roadside tests of suspected drugs. The second is to grant release of defendants on their own recognizance after an arrest for drug possession that is not supported by a reliable lab test. The third is to test suspected drugs in a lab soon after the arrest, and to await the results before accepting a defendant’s guilty plea.

Unless and until those changes occur, innocent drivers should always decline to consent when an officer asks permission to search their vehicles. Drivers who are arrested for drug possession should insist that their lawyers do everything possible to have the suspected drug tested promptly, even if that means seeking a court order for independent testing. No driver should feel pressured to plead guilty to a drug crime when the driver is innocent.

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