What do police officers look for when searching for drunk drivers on the highways?
How Police Identify Drunk Drivers on Pennsylvania Roads
Law enforcement officers are trained to detect impaired driving using specific behavioral cues that research has shown to correlate with intoxication. Understanding what police are looking for — and how their observations can become evidence against you — is important if you’re facing a DUI charge in Pennsylvania.
The NHTSA’s Driving Cues for DUI Detection
The National Highway Traffic Safety Administration (NHTSA) has developed standardized training for DUI detection. Officers are taught to look for specific driving patterns that studies have associated with a blood alcohol concentration above the legal limit. These include:
- Problems maintaining lane position — weaving, drifting, straddling a lane line, swerving, or turning with a wide radius
- Speed and braking problems — driving significantly below the speed limit, stopping too far from or past a stop line, accelerating or decelerating erratically
- Vigilance problems — driving without headlights, failing to signal, driving the wrong way, or slow response to traffic signals
- Judgment problems — following too closely, improper lane changes, driving on the shoulder or in opposing lanes
Each of these behaviors, alone or in combination, may give an officer “reasonable articulable suspicion” to initiate a traffic stop — even if no traffic violation has technically occurred.
What Happens After the Stop
Once a vehicle is stopped, the officer shifts from observing driving behavior to observing the driver directly. At this stage, the officer is looking for:
- The odor of alcohol coming from the vehicle or the driver’s breath
- Bloodshot or watery eyes
- Slurred or confused speech
- Fumbling with a license or registration
- Open containers or other evidence of alcohol in the vehicle
- Admission to drinking (“I had a couple of beers”)
These personal observations — combined with the driving behavior that prompted the stop — form the basis for the officer’s decision to administer field sobriety tests or request a breath, blood, or urine test.
DUI Checkpoints in Pennsylvania
In addition to routine traffic stops, Pennsylvania law enforcement also conducts sobriety checkpoints — fixed locations where officers briefly stop vehicles without individualized suspicion of impairment. At a checkpoint, every driver (or drivers selected according to a neutral formula) is briefly evaluated. These checkpoints are constitutional in Pennsylvania when conducted according to proper procedures.
Why This Matters for Your Defense
If you’ve been charged with DUI in Pennsylvania, the circumstances of the traffic stop are critically important. If an officer lacked a legal basis to stop your vehicle in the first place, the stop itself may be unconstitutional, and any evidence gathered as a result — including breath or blood test results — may be suppressible. An experienced Pennsylvania DUI defense attorney will examine every step of the stop and arrest to identify any procedural or constitutional violations that could affect your case.
