Traffic cops are trained to evaluate every driver subjected to a traffic stop for a DUI. That is, they are trained to look for “leading indicators” –such as slurred speech or booze breath–that the driver may possibly be under the influence. Based on the presence of these leading indicators, the cop will start to ask questions like “have you been drinking tonight?” or more presumptively “how many beers have you had tonight?” The question the cop is trying to answer is should I pull the driver out of the car to conduct a full scale DUI investigation. Once the driver is pulled out of the car, the cop will begin to ask him or her a standard series of questions which are designed to elicit incriminating information. The driver will be directed to perform several field sobriety tests, and the driver will be directed to submit to a preliminary alcohol screening test. After the breath test, the driver is arrested if the BAC estimate is over .08.
One important question to ask about this entire process is to what extent the driver is required to cooperate in developing probable cause to arrest him. The truth is that there is very little the driver is actually required to do throughout the DUI investigation. The driver is require to get out of the car at the direction of the cop, but the driver doesn’t have to answer any incriminating questions such as any or all of the questions that pertain to alcohol consumption prior to driving. Nor does the driver have to cooperate with the field sobriety tests or submit to a breath test before being arrested. Assuming a driver makes the tactical decision not to cooperate with any questions or procedures the cop uses to establish PC to arrest, there remains very little evidence remaining to support the PC. Police officers know that if they arrest someone without probable cause they can be subject to civil and criminal lability for false arrest. This gives cops the incentive to not arrest someone in marginal cases.