Reasonable Suspicion to Stop | Probable Cause to Arrest
It is usually not difficult for an officer to find reasonable suspicion to stop a vehicle. It can be almost anything that leads a officer to suspect a violation. Police stop vehicles for a variety of issues. Sometimes they suspect drunk or impaired driving. Other times, the initial stop is for something totally unrelated (expired tag, brake light out). But once an officer smells alcohol or observes some indication of impairment, the otherwise routine stop becomes a DWI investigation. At this point, the purpose is to develop proper probable cause to arrest. While reasonable suspicion is relatively straightforward, probable cause is different and requires a more substantial showing. So how do police go about establishing their case for probable cause to arrest? 
All states have adopted and employ the DWI Investigation protocols established under the National Highway Transportation Safety Administration (NHTSA). They have similarly adopted the current presumptive blood alcohol concentration level of 0.08%. While such practice may have been born out of good intentions, there is also a substantial federal financial incentive as well.
The basic DWI Investigation and Standardized Field Sobriety Testing course is 24 hours long and includes both a field practicum and written examination to complete. All police officers undergo this training, and DUI defense practitioners should also take this course. The knowledge and skills gained will prove invaluable for lawyers reviewing cases and cross-examining officers at trial. It is important to know what your adversaries will use against your client in DUI arrests.
Continuing where we left off in our Reasonable Suspicion page, the second task of an arresting officer is observation of the vehicle stop after blue lights are activated. There are 10 “post stop” clues including a sudden loss of control or difficult maintaining control of vehicle. Many people “panic” when they see a police car behind them and tend to overcompensate their driving in an attempt to “look fine.” Once stopped, the officer will make notes of characteristic behaviors in the next part of their DWI investigation.
Phase II: Personal Contact
This is the second evolution and allows an officer to personally observe a suspected drunk driver. They will look for “bloodshot” or “red, glassy” eyes. They will also be listening for “slurred speech” and smelling for any indication of alcohol or other impairing substance. Behavior can indicate impairment even if alcohol is not the impairing substance. Prescription and/or other drugs have become a real issue in DUI cases over the past few years. Here are some of the clues a police officer looks for: 
- Difficulty with vehicle controls (cannot find the door handle to get out of car; can’t turn down the volume of the radio once window down)
- Difficulty exiting vehicle (falling out of car or stumbling while attempting to exit)
- Difficulty w/license or registration (cannot find proper documents or handing officer a credit card instead of license)
- Repeating questions or comments (not able to listen or remember simple questions or requests from officer)
- Unsteady on feet (unstable or wavering once out of car)
- Leaning on vehicle (unable to stand on own without support)
- Slurred speech (classic initial finding and first sign of impairment)
- Slow to respond to officer (delay in processing simple requests or ability to answer questions timely)
- Provides incorrect information or changes answers (not able to properly process data or assimilate coherent responses)
- Alcohol odor from driver (can be difficult to gauge while outside car but may become more pronounced once inside patrol vehicle)
Phase III: Pre-arrest Screening
This is the final stage of a proper DUI investigation and involves the administration of field sobriety testing. While there may be any number of “old school” roadside tests (saying the alphabet, counting, finger dexterity, estimating time), there are only three (3) Standardized Field Sobriety Tests (SFSTs) that are recognized by NHTSA (horizontal gaze nystagmus, walk and turn, and one leg stand).
Any tests other than the SFSTs are subject to challenge, since they have not been tested for demonstrable reliability. It should also be noted that the results are invalidated if these SFSTs are not administered exactly as required. Otherwise, they are no longer “standardized” and cannot be considered reliable indicators of impairment.
Of course, these tests are extremely difficult to perform under the best conditions, and the vast majority of people attempting them fail as they are not familiar with them. Police officers become proficient only after practicing the complex balancing maneuvers many times. If they do not consistently and regularly demonstrate the tests, they too can lose the ability to perform them.
Even at trial when they are asked to demonstrate for the jury, officers can “sway” or “step off line.” The simple reality is that we are not physiologically designed to walk “heel to toe” without use of our arms to counter-balance. We are similarly not accustomed to standing on one leg for up to 30 seconds without extending our arms to maintain balance. Impairment can certainly enhance these issues, but it is difficult to perform these “tests” even when fully sober.
The final test in North Carolina involves the use of a “portable breath tester (PBT).” If protocol is followed, the officer will ask a suspected impaired driver to perform two (2) separate tests at least five (5) minutes apart. Many of our clients question why such test is necessary, especially when they have answered “yes” to “have you had anything to drink tonight?” While many officers will share the “numerical reading” of the PBT, such figure is NOT admissible at trial.
Thankfully, the legislature has realized how utterly unreliable these devices are. Only a “positive” or “negative” reading is relevant, not the actual number on the PBT. Again, given our dependence on prescription and other drugs, not all impaired driving cases are based on alcohol.
To Arrest or Not to Arrest 
If the officer has followed their training, they are now at a point where they can make the all important decision of whether there is sufficient probable cause to arrest. The NHTSA standard protocol mandates a thorough and complete investigation following the outline above. If properly completed, there is evidence to arrest and proceed to more formal breath testing back at the police station. Unfortunately, there are too many cases where the officer merely relies on their years of experience and intuition that a person is unsafe to drive. Even if their “gut feeling” is later shown to be correct, the case should still fail as there was improper probable cause to arrest. These are the legal arguments that can make a real difference in the outcome of your case. It also protects us all as the bar of justice is set by how courts and judges adjudicate the weakest case.