What are some potential defenses to an allegation of DUI?

DUI cases in Pennsylvania offer a range of potential defenses depending on the specific facts of each arrest. The complexity of DUI law — spanning constitutional protections, scientific evidence, and detailed statutory requirements — means that even cases involving chemical test results above the legal limit may have viable defenses worth pursuing.

Was There Reasonable Suspicion for the Traffic Stop?

A lawful DUI arrest begins with a lawful stop. An officer must have reasonable articulable suspicion of a traffic violation or criminal activity before initiating a traffic stop. Common bases for DUI stops include speeding, swerving, running a red light, or equipment violations. If the officer lacked sufficient reasonable suspicion — if the stop was pretextual, based on a mistake of law, or without factual basis — a motion to suppress all evidence from the stop may succeed, effectively ending the prosecution.

Were You Actually Driving or in Control of the Vehicle?

Pennsylvania’s DUI statute requires the Commonwealth to prove that the defendant was driving, operating, or in actual physical control of the movement of a vehicle. When a driver is found in a stationary, parked vehicle, the question of actual physical control is contested. Courts examine whether the keys were in the ignition, whether the engine was running, the position of the driver in the vehicle, and other circumstances to determine whether actual physical control existed. Ambiguous situations present genuine defense opportunities.

Was the Chemical Test Properly Administered?

Chemical test results are admissible in Pennsylvania only if they were obtained in compliance with statutory and regulatory requirements. Potential challenges include:

• Breathalyzer calibration: The device must be properly calibrated and certified. Calibration and maintenance records are discoverable and may reveal deficiencies that undermine the result’s reliability.
• Observation period: Before administering a breath test, officers must observe the subject for a mandatory period to ensure no belching, vomiting, or oral alcohol contamination occurred. Failure to comply with this requirement can invalidate the result.
• Blood draw procedures: Blood samples must be collected by qualified personnel, preserved with the correct anti-coagulant and preservative, maintained with chain of custody documentation, and analyzed by an accredited laboratory. Any break in this chain can support a challenge to admissibility.
• Rising blood alcohol defense: Because BAC rises for a period after alcohol consumption, the BAC at the time of testing may exceed the BAC at the time of driving. Expert testimony on alcohol absorption rates can establish that the driver’s BAC was below the legal threshold while actually operating the vehicle.

Were Your Constitutional Rights Violated?

Several constitutional protections apply during a DUI investigation:

• Fourth Amendment (search and seizure): Unlawful stops, unlawful arrests without probable cause, and warrantless blood draws without consent or exigent circumstances may all support suppression of evidence.
• Fifth Amendment (self-incrimination): Statements obtained through custodial interrogation without Miranda warnings may be suppressed.
• Sixth Amendment (right to counsel): Post-arrest denials of requests to speak with an attorney may affect the admissibility of subsequent statements or test results.

Medical and Physiological Conditions

Certain medical conditions can mimic signs of impairment or affect chemical test results. Diabetic ketoacidosis can produce substances that certain breathalyzers interpret as alcohol. Acid reflux or GERD can cause mouth alcohol contamination affecting breath test readings. Neurological conditions, inner ear disorders, and physical injuries can impair performance on field sobriety tests for reasons entirely unrelated to alcohol. Medical evidence from treating physicians can provide an alternative explanation for observations that the prosecution attributes to impairment.

Checkpoint Procedural Challenges

DUI checkpoints must comply with specific constitutional requirements under both federal and Pennsylvania law, including advance public notice, a neutral vehicle selection formula, and limitations on the duration of stops. Failure to comply with these requirements can render checkpoint stops unconstitutional, supporting suppression of all resulting evidence.