A driver must have committed a traffic violation or otherwise for an officer to pull the person over. In order for an officer to request the driver to submit to an alcohol screening test, they must have reasonable suspicion. For example, if a driver is following all traffic safety laws, the officer has no reason to pull the driver over. If the driver exhibits no signs of being under the influence of any substance, including alcohol, and does not admit to having been under the influence, the officer does not have authority to request a drug or alcohol screening test.
The driver may then be asked to submit to a blood test if the officers believe they may be under the influence of additional substances. However, they gain their initial authority to request an alcohol screening test because of the use of alcohol. Once the blood test results come back, and they demonstrate drug use, the driver may then have additional evidence against him, even though the driver was initially pulled over and test for alcohol alone.
Thissconcept is best described through an example. Dana has two beers at a friend’s place. She also takes more than the allotted dose of sleep medicine. She hasn’t been sleeping well lately and decides that if she takes the medication prior to leaving her friend’s place, by the time she gets home she will be ready to fall asleep. Dana speeds on the way to her house. She is pulled over by an officer for speeding (valid traffic violation). The officer smells the beer on her breath and asks her if she has been drinking. Dana responds yes, that she has had two beers (reasonable suspicion by admission). The officer then asks her to submit to a field sobriety test. Dana assumes that she has only had two beers so her BAC is low, and she will easily pass the tests and readily submits. She blows a .02.