What is the two-hour rule for DUI tests in Pennsylvania?

Last updated October 4, 2026.

Pennsylvania's blood alcohol tiers are measured by a breath or blood test of the alcohol in your system within two hours after you drove. A sample taken later still counts only if the Commonwealth shows good cause for the delay and proves you did not drink or use a controlled substance between the arrest and the test (75 Pa.C.S. 3802(g)). The rule does not apply to the general impairment charge under 3802(a)(1), which is about being unable to drive safely, not a number.

That makes the clock one of the first things to check in any DUI file with a test result. This page explains which charges use the window and what the exception requires. For penalties by tier, see our main DUI defense page.

How does the two-hour clock work, step by step?

1. The clock starts when you last drove. The statute measures from when the person "has driven, operated or been in actual physical control of the movement of the vehicle," not from the stop or the arrest.
2. The sample is taken. A breath test at a station or a blood draw at a hospital records a time on the printout or the lab paperwork.
3. The result is matched to a tier. Under 0.08% is below the adult per se line; 0.08% to under 0.10%, 0.10% to under 0.16%, and 0.16% or more are the three adult tiers (3802(a)(2), (b) and (c)).
4. If the sample came after two hours, the Commonwealth must prove both parts of the 3802(g) exception for the number to count.
5. If it cannot, the result cannot establish the number-based charge on its own, and the case turns on what other charges and evidence remain, often the general impairment charge under 3802(a)(1).

Which DUI charges use the two-hour window?

Each number-based section uses the same phrase: the alcohol concentration in the person's blood or breath must reach the level "within two hours after the individual has driven, operated or been in actual physical control of the movement of the vehicle." PennDOT's manual summarizes the limits the same way: 0.08% for drivers 21 and older, 0.02% for drivers under 21. Commercial drivers also face a separate disqualification, explained in what a DUI means for a commercial driver's license.

When can a test taken after two hours still be used?

Section 3802(g) allows a later result to establish the blood alcohol element when both of these are shown:

• the Commonwealth shows "good cause explaining why the chemical test sample could not be obtained within two hours"; and
• the Commonwealth establishes that the person "did not imbibe any alcohol or utilize a controlled substance between the time the individual was arrested and the time the sample was obtained."

Both parts are the prosecution's burden. The statute does not define good cause, so whether a particular delay qualifies is argued on the facts of each case. Act 58 of 2025 extended the same exception to the new offense of DUI following diversion under 3802(h).

Why does a tier line matter so much?

The tier sets the mandatory minimum. For a first offense, 75 Pa.C.S. 3804 provides six months of probation and no mandatory jail at the general impairment tier, at least 48 hours at the high rate, and at least 72 hours at the highest rate. The tier also sets the ARD license suspension: none below 0.10%, 30 days from 0.10% to under 0.16%, and 60 days at 0.16% or higher or when the BAC "is not known" (75 Pa.C.S. 3807(d)). Delaware County's ARD application uses the same lines for its Tier I, II and III community service hours.

Here is what each line means for a first offense under the current statute:

So a result just over 0.10% or 0.16%, or a sample drawn well after the two-hour mark, deserves a close look. If a result cannot be used for the tier it was charged under, what remains of the case depends on the other evidence. The full first-offense picture is on our first offense DUI page.

What rules apply to the test itself?

Timing is not the only requirement. Under 75 Pa.C.S. 1547(c):

• Breath tests must be performed on devices approved by the Department of Health, using procedures set by the Departments of Health and Transportation, by a person trained in an approved program; the device must have been calibrated and tested for accuracy as the regulations require.
• Blood tests done in Pennsylvania must be performed by a clinical laboratory licensed and approved by the Department of Health, or by a State Police crime lab.

You may also request the results of any chemical test, and you were entitled to have a physician of your choosing perform an additional test (1547(g) and (h)). The small roadside breath test some officers use before an arrest only helps the officer decide whether to arrest (1547(k)). If you refused testing instead, the issues are different; see what happens if you refused a breath or blood test.

What records show whether the two-hour rule was met?

• The affidavit of probable cause, which describes the stop and the arrest.
• The breath test printout or the lab report, with the time the sample was taken.
• Hospital or ambulance records if blood was drawn during treatment.

In Delaware County DUI-ARD cases, the county's application says the assistant district attorney will, if able, provide the driving history, criminal record check and lab report at the preliminary hearing, which is one early chance to see the timeline. For the rest of the case schedule, see what happens after a DUI arrest in Delaware County. For how the tier lines feed into ARD, read DUI ARD in Delaware, Chester and Montgomery counties.

A challenge to the timing is usually raised in the omnibus pretrial motion, which is due within 30 days after formal arraignment unless the grounds were not known in time (Pa.R.Crim.P. 579(A)). In Delaware County that motion is filed in the Court of Common Pleas in Media; our guide to what to expect at the Delaware County Courthouse shows where it fits.

What changes the answer?

• When the driving ended. A driver found in a parked car raises the question of when the person last drove or was in actual physical control, which is where the two hours start.
• Breath or blood, police or hospital. Each kind of test has its own equipment and lab rules under 1547(c), and hospital draws come with medical records that show the times.
• A crash. A general impairment charge with a crash that caused injury or property damage is sentenced in the high rate tier even without a number (3804(b)). The rest of the crash picture is in what happens when a DUI involves a crash with injuries.
• Drugs. The controlled substance sections in 3802(d) have no two-hour language. For blood tests, the Department of Health sets minimum levels a result must reach to be admissible in a 3802(d)(1), (2) or (3) case (1547(c)(4)).
• Your age or license. Drivers under 21 face a 0.02% line, and commercial drivers 0.04%, both measured within the same two hours.
• No result at all. When the BAC "is not known," the ARD suspension is 60 days, the same as the top tier (3807(d)(3)); a refusal adds its own suspension.

For example: a hospital blood draw after a crash

Here is a hypothetical. A driver slides into a guardrail at 11:10 p.m. Police arrive, arrest the driver at 11:40 p.m., and an ambulance takes the driver to the hospital, where blood is drawn at 1:35 a.m., about two hours and 25 minutes after the driving ended. The result is 0.11%, and the driver is charged in the high rate tier.

Because the sample came after two hours, the 0.11% counts toward the high rate charge only if the Commonwealth shows good cause for the delay, for example medical treatment that had to come first, and proves the driver had nothing to drink or use between the arrest and the draw. If it cannot, the number alone does not establish the 3802(b) charge, and the case turns on the general impairment charge and the officer's observations, where the crash itself still matters for sentencing. This example is only an illustration; every case depends on its own facts.

What mistakes do people make about the two-hour rule?

• Counting from the arrest. The two hours run from the driving, not the handcuffs.
• Assuming a late test ends the case. The exception exists, and the general impairment charge does not depend on a number.
• Relying on the roadside device. That preliminary breath test only helps the officer decide whether to arrest (1547(k)).
• Not asking for the results. You are entitled to the results of any chemical test on request (1547(g)).
• Forgetting the hospital records. They often hold the most precise times for the draw and the treatment.
• Waiting past the motion deadline. Timing problems belong in the omnibus pretrial motion, due 30 days after arraignment.

What should I do this week?

1. Write down, as best you remember, when you last drove, when you were stopped, when you were arrested and when the test happened.
2. Ask for a copy of the breath printout or lab report through your lawyer.
3. List any hospital or ambulance involvement so those records can be requested.
4. Note whether anything was eaten or drunk after the arrest; the 3802(g) exception turns on it.
5. Keep every PennDOT letter, since the tier also drives the suspension.
6. Check how your tier affects ARD in who is eligible for DUI ARD in Delaware County.

Frequently asked questions

When does the two-hour clock start?

When you last drove, operated or were in actual physical control of the movement of the vehicle. The stop, the arrest and the trip to the station all happen inside that window or after it.

Does the two-hour rule apply to a drug DUI?

No. The controlled substance offenses in 3802(d) do not use the two-hour language, although blood results must meet the minimum levels the Department of Health sets for admissibility (1547(c)(4)).

Can I be convicted without a valid test result?

Yes, under 3802(a)(1), if the evidence shows alcohol made you incapable of safely driving. That charge depends on observations, driving and other evidence rather than a number.

Does a late test change whether I should fight the case?

It can, because it may change the tier, the minimum sentence and the ARD suspension. Weigh it with a lawyer using whether to accept ARD or fight a DUI.

What happens to my license if the result is thrown out?

The suspension on a conviction follows the offense you are actually convicted of (3804(e)), so a lower tier can mean a shorter or no suspension. Our page on when PennDOT suspends your license after a DUI explains the timing.

Call Giribaldi Law at (610) 891-8303 or contact us online for a free consultation and a review of your test timeline.