What Are Common Police Mistakes That Can Affect a DUI Case?
August 7, 2026
Police errors during a DUI/drunk driving stop can weaken the evidence used against a driver. Mistakes such as an unlawful traffic stop, an improperly administered field sobriety test, or a mishandled breath or blood sample often give a West Chester DUI lawyer grounds to challenge the charges. Reviewing police conduct closely is a critical step in building a strong criminal defense.
What Common Police Mistakes Affect DUI Arrests in West Chester?
Officers in Chester County must follow specific procedures when stopping, testing, and arresting a driver suspected of DUI. When they skip steps or misapply the rules, the case against the driver can become vulnerable. Common issues include:
- Stops made without valid cause
- Poorly conducted field sobriety tests
- Chain of custody problems with blood samples
- Failure to read a driver their rights at the correct time
Each of these errors can affect whether evidence holds up in court. A defense built around these details often changes the outcome of a case far more than arguing guilt or innocence alone.
How Do Improper Traffic Stops Impact a DUI Case?
Police need reasonable suspicion to pull a driver over. This means an officer must observe an actual traffic violation or sign of impaired driving, such as swerving on Route 202 or ignoring a stop sign near the West Chester Courthouse on North High Street. If an officer cannot point to a specific, valid reason for the stop, any evidence gathered afterward may be suppressed. Courts take this requirement seriously because it protects drivers from random or biased stops. Dashcam footage and radio logs are often reviewed closely to confirm whether the stated reason for a stop actually matches what happened.
What Field Sobriety Test Errors Occur Often?
Standardized field sobriety tests, including the walk and turn, one-leg stand, and horizontal gaze nystagmus test, must be given in a specific way. Uneven pavement, poor lighting, or bad weather along roads such as Route 322 can affect a driver’s balance and performance without impairment being the cause. Officers also sometimes fail to ask about medical conditions, footwear, or injuries that could explain poor results. These tests must be administered under consistent conditions to produce reliable results, and any deviation can be challenged later. A test given on a sloped shoulder or in the dark without proper lighting is a common example that defense attorneys look for right away.
How Can Breathalyzer and Blood Test Mistakes Affect Evidence?
Breath and blood tests require proper calibration, storage, and handling. A breathalyzer device that has not been maintained on schedule can produce inaccurate readings. Blood samples that sit too long before testing, get mislabeled, or pass through too many hands without documentation may not hold up as reliable evidence. Pennsylvania officers and labs are expected to follow certain protocols, and gaps in this process often become a central issue in DUI defense. Maintenance logs, calibration records, and laboratory paperwork are frequently requested to check whether these standards were actually met in a specific case. If your case goes to court, and the prosecutor cannot produce these, the charges against you could be dismissed, or you may win an acquittal.
What Happens When Police Fail to Follow Miranda Procedures?
Once a driver is in custody, officers must read Miranda rights before conducting further questioning. If police continue asking questions without providing this warning, statements made by the driver may not be usable in court. This mistake does not always dismiss a case, but it can limit what evidence the prosecution presents at trial. The issue is knowing exactly when a driver was considered in custody, rather than simply being questioned during a stop, because this can be a determining factor.
Reviewing every part of a DUI arrest, from the initial stop to the final test results, gives a driver a clearer picture of whether the process was handled correctly. Small errors in procedure can carry significant weight in court, and identifying them early often shapes the direction of the entire case.
West Chester DUI Lawyer at the Law Offices of Heather J. Mattes Is Ready to Help With Your DUI Stop
The West Chester DUI lawyer at the Law Offices of Heather J. Mattes is ready to review the details of a DUI stop and identify any mistakes made by police. Our experienced legal team will fight to protect your rights. You can schedule a free initial consultation 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.