What Is the “Two-Hour Rule” in Pennsylvania DUI Cases?
December 5, 2025
If you are the defendant in a driving under the influence (DUI) case in Pennsylvania, you have legal rights. The prosecutor intends to use evidence against you that can prove that you were impaired when you were driving. However, that evidence needs to have been taken in close time proximity to when you were stopped by police on reasonable suspicion of drunk driving. If too much time has passed before law enforcement has obtained evidence of potential intoxication, the proof may be inadmissible in court under the two-hour rule. An experienced DUI lawyer can review the evidence that the prosecutor proposes to use against you and challenge it in court when necessary.
How Does the Two-Hour Rule Apply to Your Case?
One of the main protections that you have in a DUI case is that the evidence that is being used against you must be admissible under the law. Not only does there need to be a continuous chain of custody over the evidence, but it must also be authenticated. You may be able to raise doubts about the evidence if it has either been corrupted or if it was taken too long after the traffic stop.
It is a scientifically accepted fact that your blood alcohol content can rise and fall over time after alcohol has supposedly been consumed. There is even a chance that your blood alcohol content can go up some time after you have been taken into custody. Either way, the reliability of the evidence is not the same if it has taken too long for the police to draw blood from your system.
No matter what, you are always free to challenge the evidence being used against you for various reasons. Even if law enforcement drew the blood sample within two hours, you may still be able to argue that the evidence is faulty or that it lacks the proper chain of custody. An experienced DUI lawyer can review your case and help determine whether you have any potential defenses or ways to go after the evidence that the prosecutor is proposing to use against you in court.
Are There Exceptions to the Two-Hour Rule?
There are some exceptions to the two-hour rule that can keep it from applying in your case. In some cases, the driver who has been arrested refuses to undergo a blood alcohol test. Then, the police officer must go to a court and seek a search warrant to draw blood for testing. It can take some time to fill out the paperwork and establish probable cause, such that a magistrate would approve a search warrant. If this has happened, the two-hour rule would be inapplicable because the police were not able to be diligent in conducting the testing within the required amount of time.
There could also be exceptions based on the fact that police exercise all reasonable diligence, yet still fail to conduct a blood test within two hours. In addition, the two-hour rule may not apply if the driver who was arrested needed medical attention, and the blood could not be drawn within the required amount of time. Even if the blood test evidence is suppressed, the prosecutor may still be able to win a conviction if they can otherwise show that you were impaired without having to use the blood test evidence. Nonetheless, having any chemical evidence against you thrown out of court can give you an edge when you are defending against DUI charges or trying to negotiate a plea deal with the prosecutor.
West Chester DUI Lawyer at The Law Offices of Heather J. Mattes Will Fight to Get You the Best Legal Result
If you have been charged with driving while impaired, speak to a West Chester DUI lawyer at the Law Offices of Heather J. Mattes. We can help get to the bottom of your case and work to obtain the best possible legal result. You can schedule a free initial consultation with a DUI attorney by filling out an online contact form or by calling us today at 610-431-7900. Our office is in West Chester, Pennsylvania, and we serve clients in the surrounding areas.