Since Pennsylvania legalized the use of medical cannabis, I have seen a significant upswing in people who have been charged with DUI for driving under the influence of cannabis, or “marijuana.” Most of these clients are quite surprised by the fact that the very same government that issued them a license to legally use medical cannabis is now gleefully prosecuting them for using that very same drug.

Pursuant to DEA Regulations, cannabis is a Schedule I Drug. Under 75 Pa. C.S. §3802(d)(iii) someone who drives with any amount of the metabolites (the chemical byproducts left in your system as the drug breaks down) of any Schedule I Drug in their system is guilty of violating the Pennsylvania DUI law.

There is no exception in the DUI law for medical cannabis cardholders. See my earlier article on the perverse evolution of DUI Law.

According to the U.S. National Library of Medicine, the metabolites of cannabis are detectable in the user’s system for up to thirty days after they stop using the drug. Because of this, if you are a medical cannabis user, you risk a DUI every time you get behind the wheel.

Until the DUI law changes, the only way you can be legal enough to drive is to discontinue the use of cannabis for thirty days. In the meantime, while we are waiting for the law to change to accommodate lawful users of cannabis-based medicines, if you get pulled over, follow my previous advice on what to do when you are stopped for DUI.

Already have a DUI case? Explore Joe’s Practice Areas for more information on how we can help you settle your case.

Driving in an impaired state is dangerous and no one should be doing it.  In my previous blog (The Perverse Evolution of DUI Law) under existing law, you can be sober at the time you are pulled over and be charged with, and even convicted of, DUI because of past or even future intoxication that may or may not have been while driving.  I also discussed how the government is railroading people who have less than the BAC limit in their system into “general impairment” DUI convictions.

Clients and followers alike have been asking me for some time to put together some tips on what to do during a DUI stop.  Of course, I shared my strategies with friends and family, but I held off on writing on this subject for fear of encouraging people to engage in driving under the influence.

As you read this, please keep in mind that this paper is directed at Pennsylvania DUI law only.

If you haven’t read my article on the perverse evolution of DUI law, now might be a good time to do so, because it shows how you don’t need to actually be DUI to get convicted of DUI.

The “Typical” DUI Stop and Arrest.

In this blog, I am going to talk about seven specific parts of a DUI case:

  1. Traffic Violation/Probable Cause to Stop
  2. Initial Interaction with Police
  3. Questioning About Alcohol and Drug Use
  4. Field Sobriety Testing
  5. Arrest and Transport to Testing Facility
  6. Testing
  7. Results and Filing of Criminal Charges

Probable cause to stop

The vast majority of DUI cases begin with the driver being pulled over by police who witness a violation of the motor vehicle code.  This violation gives police probable cause to stop the car and issue a ticket.  Common violations include failure to fully stop at a stop sign, speeding, expired inspection, burned out tail light, and a number of things that rarely result in more than a fine.

Initial Interaction with Police

After you pull over, the officer will approach your car and ask you to produce your license, registration, and proof of financial responsibility (insurance card).  While you are fumbling (typically in the dark) for those, the police officer will continue to talk to you and ask you questions.  At this stage, the officer is already beginning to assess your ability to handle multiple complex tasks under the stress of a pullover.  I suggest that you don’t engage in this stress testing.  If the officer asks a question, stop fumbling, sit up straight and answer it.  Do this a few times and you may find that the officer will knock it off and wait for you to produce the documents they requested.

Questioning about alcohol and drug use

If the officer suspects that you may be intoxicated, they typically inquire as to whether you have been using alcohol or drugs.  This is a “Catch-22”-type question.  Particularly in regard to alcohol use, the officer will almost certainly have smelled it on you.  If you lie and deny your use of alcohol, later testing will reveal this to have been a lie.  On the other hand, if you admit alcohol use, you are incriminating yourself.

Many people try telling a little white lie that might explain the odor of alcohol on their breath without incriminating themselves, “Yes officer, I had a beer after work.”  This never works. And you are answering a question the officer didn’t ask.  They didn’t ask how much you had to drink because they don’t care, all they are trying to establish is that you used any alcohol.  You are trying to answer a question that hasn’t been asked, and law enforcement is trained to see this as an attempt to mislead.

We have all heard stories about people “talking their way out of” a DUI arrest.  You aren’t dealing with the same DUI law your parents did. This is an urban legend from a time long passed, and may not have been all that true, even then.

You should understand that the moment an inquiry about drug or alcohol use starts, you are almost certainly going to be arrested for DUI.

All too often, drivers in this situation focus on doing what they can to avoid being arrested.  They honestly believe that if they are good little boys and girls, answer questions truthfully, and are otherwise compliant that the officer will just “let them go.”

This is complete nonsense.

What law enforcement officer in their right mind would knowingly allow someone who might be intoxicated to simply drive off?  It’s not going to happen.

The officer isn’t trying to determine if you are safe to drive.  The officer is only collecting evidence to prove that it was reasonable for them to believe that you weren’t safe to drive and that it was, therefore, reasonable to arrest you.  Simply put the officer is building a court case, not deciding whether to arrest you.

What you do, or do not do, in the next 15 minutes will have massive effects on how that court case comes out.

But first, you have to stop thinking about avoiding arrest.  Your efforts to talk your way out of being arrested and being allowed to simply drive off are coming out of your mouth with the odor of alcohol on them and may be slurred.  Stop trying to avoid being arrested and start doing things that will help you to avoid being convicted.

Of course, you have been trained to be respectful to the police, to help them and to tell the truth.  It may be difficult for you to envision yourself refusing to answer questions.  You may still believe that you are going to avoid arrest, or you may be intimidated by being pulled over.  Stand up for yourself!  You are about to be railroaded into a DUI, potentially when you may be legally or actually sober, don’t make it easier on them.

You aren’t required to answer questions about drug or alcohol use.  Don’t answer them!  I will explain why towards the end of this blog, but for now, what you need to know is that you should be polite and respectful, and simply refuse to answer questions about drug and or alcohol use.  I suggest a response along the lines of “With respect Officer, I am not going to answer any questions.”

And don’t answer any questions.  You may find that the officer may ask you to explain your bloodshot eyes, slurred speech, or the odor of alcohol or marijuana he claims to notice.  You may feel a “tug” to respond or deny.  Don’t.  Don’t answer questions, and don’t allow yourself to be baited into talking either.

Field Sobriety Testing

Many of us are aware that there are penalties for refusing to be tested for DUI.  Section 1547(a) of the Motor Vehicle Code, sometimes called the “Implied Consent Law,” states that if you drive a car, you have  impliedly consented to be tested for DUI:

Any person who drives, operates or is in actual physical control of the movement of a vehicle in this Commonwealth shall be deemed to have given consent to one or more chemical tests of breath or blood for the purpose of determining the alcoholic content of blood or the presence of a controlled substance if a police officer has reasonable grounds to believe the person to have been driving, operating or in actual physical control of the movement of a vehicle in violation of section 1543(b)(1.1) (relating to driving while operating privilege is suspended or revoked), 3802 (relating to driving under influence of alcohol or controlled substance) or 3808(a)(2) (relating to illegally operating a motor vehicle not equipped with ignition interlock).

Section 1547(b) of the Motor Vehicle Code provides that if you refuse to be tested, the police are to report this refusal to PennDOT and that PennDOT is to automatically suspend you for refusing to be tested:

If any person placed under arrest for a violation of section 3802 is requested to submit to chemical testing and refuses to do so, the testing shall not be conducted but upon notice by the police officer, the department shall suspend the operating privilege of the person.

It is important for the reader to understand that the implied consent law gives your consent to chemical testing of your blood or breath only.  If you don’t believe me, re-read 1547(a), or look it up on your own.

The automatic license suspension set out in Section 1547(b) only applies if you refuse post-arrest chemical testing of your blood or breath.

Field Sobriety Tests are not chemical tests of your blood or breath.  The standard “walk and turn”, “finger to nose”, and ’follow my flashlight” tests done in the field are obviously not chemical tests of your blood or breath.

Preliminary breath testing done in the field by police is not one of the chemical tests to which you consent under Section 1547(a).  Wall v. Commonwealth, 114 Pa. Commonwealth Ct. 397 (1989), 539 A.2d 7.  See Also Section 1547(k) for the proposition that refusal to submit to a preliminary breath test shall not be considered for the purposes of Section 1547(b).

Furthermore, these tests are commonly conducted before the arrest.  The sanctions of 1547(b) only come into play if you refuse chemical testing of your blood or breath after having been arrested.

You have not “impliedly consented” to any field sobriety testing at all, and you cannot be penalized for refusing pre-arrest sobriety tests of any type.  My advice is to politely refuse to perform these tests.  Something along the lines of, ”With respect Officer, I am not going to perform any field sobriety testing.”

You may find yourself faced with a surly officer at this point.  The police certainly won’t like you refusing to perform tests that you aren’t required to perform and serve only to further incriminate you.  The officer may threaten you with arrest if you refuse to do the tests, or say something along the lines of, “I have to warn you that if you refuse to perform the tests required by the law your license will be automatically suspended.”

These are two common responses from law enforcement when confronted with a driver who refuses to perform field sobriety tests and I will discuss the phrases in the following two parts.

“If you don’t perform these tests, I am going to be forced to arrest you for DUI”

For starters, you can be arrested for DUI any time the officer believes that you are DUI.  Field sobriety tests are not required in order to arrest you for DUI.  If field testing is conducted, it need not be “standard” tests.  Moreover, you can still be arrested, even if you “pass” the field sobriety tests via  Cole v. Commonwealth, 909 A.2d 900 (Pa. Commw. Ct. 2006)  See also Commonwealth v. O’Neill 100 Pa.Cmwlth. 448 (1986), 514 A.2d 1008.

The officer doesn’t need the tests to arrest you and they aren’t “forced” to arrest you for failing to perform them.  If the officer believes that you are DUI, they can arrest you.  But they can’t force you into post-arrest chemical testing of your blood or breath unless they have reasonable grounds to believe that you were DUI.  (75 Pa. C.S. §1547)

The field sobriety tests are an effort to document the reasonable grounds required to trigger your “implied consent” to chemical testing, and the right to suspend your license if you refuse post-arrest chemical testing.

Of course, if you do the tests, it will be filmed and introduced into evidence to support the contention that the officer had reasonable grounds to believe that you were DUI.

“Sir, I have to warn you that if you refuse to perform the tests required by the law your license will be automatically suspended.”

This is another misleading and threatening statement police commonly use to coerce people into performing field sobriety tests.

The statement is factually true:  if you refuse to perform the tests required by the law, your license will be suspended.  The problem is that the field sobriety tests aren’t the tests required by the law. Remember, the law only requires that you submit to chemical testing of your blood or breath and you can only be sanctioned for refusing if these tests are requested after the arrest.

“Do you have some reason that you can’t perform the tests?

This is another classic, and it is pure bait.  Here the officer is trying to get you to give a reason as to why you “can’t” do the tests.  You didn’t say that you “can’t” do the tests, you said that you “won’t” do the tests.  You are perfectly capable of performing the tests, perhaps even passing them, you are just refusing to perform the field sobriety tests because they only exist to allow the officer to collect further incriminating evidence.  Now is a good time to remind the officer that, “With respect Officer, I am not going to answer any questions.”

Arrest and transport to testing facility 

So you have refused to admit to alcohol or drug use, and you have refused to perform the field sobriety tests and give the police evidence with which they can convict you.  At this point, the officer is going to arrest you for suspicion of DUI.

They may even take one last try at getting you to incriminate yourself with a comment like, “Well then, you leave me no choice but to arrest you for suspicion of DUI.”  Notice here that the officer hasn’t formally arrested you, they are just trying the “I have to arrest you” gambit in a different way.  If they actually arrest you they won’t say “I am going to have to arrest you,” they will say, “I am placing you under arrest.”  Once they formally arrest you, they have to stop asking questions or read you your Miranda rights – in either case, they may not get that all important admission of guilt.

Either way, you are going to be placed under arrest.  Being arrested is a dramatic event.  Police become quite assertive during the arrest process in order to effectuate the arrest as quickly as possible and with the lowest risk of triggering your “fight or flight” response.  The police do not have to “read you your rights” under Miranda v. Arizona, 384 U.S. 436 (1966) unless they plan on questioning you further, and they commonly do not read DUI arrestees their rights.

After you are “cuffed” the police will search your person and will likely secure your vehicle in place or call for a tow truck.  You will then be placed in the police vehicle for transport to wherever they perform post-arrest chemical testing of your blood or breath, which is usually a hospital, but sometimes a police station.

It is very important that you keep quiet during transport to the testing facility. The interior of a police car that is transporting an arrestee is usually being recorded on audio and video.  You will experience something of a “come down” now that your fear of being arrested passes, and people commonly start talking to police, even admitting to being intoxicated.

Don’t talk to the officer in the police car, keep your mouth shut.  The evidence is still being collected until you are released from police custody.

Although just a few minutes ago they were full of curiosity, during transport the officer will not ask you any more questions.  The officer transporting you may respond to things you say, but won’t ask questions or start conversations.

Miranda requires that you be read your rights before being subjected to post-arrest interrogation. They haven’t read you your Miranda rights and they can’t ask you questions until they have done so.  The reason they didn’t read you your rights is that they know that people commonly make admissions after being arrested and if they read you the Miranda warnings you might realize that, “Anything you say can and will be used against you.”


As I stated earlier, you will be transported to a testing facility for the administration of post-arrest chemical testing of your blood or breath.  These are the tests that you have “impliedly consented” to under Section 1547(a).  If you refuse to perform or allow these tests, the police themselves will notify PennDOT of your refusal and your driving privilege will be suspended pursuant to Section 1547(b).

The most common testing performed today is a blood draw, because that allows the government to check you for drugs in addition to alcohol.  This means a needle.  You do have a right to refuse, but your basis for refusing (fear of needles, religious conviction, wanting to speak with an attorney first, etc.) doesn’t matter.  If you refuse post-arrest chemical testing of your blood or breath the police will report you to PennDOT as a refuser and your license will be suspended by PennDOT.

Refusing to perform or submit to the required post-arrest tests of your blood or breath is a separate offense from DUI.  You can, in theory, be convicted of both refusing to be tested and of DUI, in which case you will serve the punishment for both offenses.  My advice is to submit to the required post-arrest tests of your blood or breath.

Results and filing of criminal charges

Criminal charges will be filed if testing reveals even the metabolites of an illicit or un-prescribed drug or any amount of alcohol at all, even amount below the so-called “BAC Limit” of 0.08%.

Depending on local policy and the ability to do so, you may be released to a friend or held in jail.  If you are held in jail, you may be arraigned, printed, and put through initial processing that day.  If you are released to a friend, you may not hear from the criminal process for a few weeks when a notice of preliminary hearing and fingerprint order arrive in the mail.  But they won’t forget about you.

Maybe it’s not illegal, but isn’t refusing the field sobriety tests disrespectful?

The police really want you to perform the field sobriety tests because they want to establish that they had reasonable grounds to believe that you were driving while “DUI” and therefore that they had the right to arrest you and compel a chemical testing of your blood or breath.

Earlier in this blog, I showed you how some police may try and coerce you into performing the field sobriety tests by claiming that your refusal to do so will “force” them to arrest you.  I also showed you the police trick of acting like you claimed that you couldn’t perform the tests, i.e. “Is there some reason why you can’t perform the tests?” when in fact you had simply refused to perform the tests.   I even showed you the trick of them trying to make you think that the law requires you to perform field sobriety tests.

Another “trick” law enforcement may use to coerce you into those field sobriety tests is to feign offense, or even anger, and claim that by refusing to take the field sobriety tests and/or field breathalyzer you are somehow being “disrespectful” to law enforcement.

In a lot of ways, the police feigning offense and outrage to trick you into performing field sobriety tests or field breathalyzer tests is pretty cynical.  We have all been taught since we were children that if we were good little boys and girls – obedient and respectful – we would be rewarded for those characteristics.  We were also taught that if we were disrespectful or disobedient, that we would be punished.  Here, the police are claiming that you are being disrespectful to coerce you into performing a test that you have already refused, that isn’t required, and serves only to incriminate you!

You are not being disrespectful, you are standing up for your rights.  You are going to be polite, respectful, and non-confrontational.  You will start every refusal with the phrase “With respect officer.”  And you will, in fact, perform the tests that the law requires you to perform, the post-arrest chemical tests of your blood or breath.

Why are you telling us to refuse?

Even if you refuse to answer questions and refuse field sobriety testing, you will still be charged and you may, in fact, still end up pleading or being found guilty.

The police don’t need your admission of drug or alcohol use, the field sobriety tests, or even a field breathalyzer sample to arrest you for suspicion of DUI.  Once you are arrested, you do have to submit to post-arrest testing of your blood or breath.

Your refusal to admit drug or alcohol use and your refusal to perform field sobriety tests and/or field breathalyzer testing denies law enforcement the smooth transition from probable cause to pull you over to probable cause to arrest you and take you in for testing that your admission or drug or alcohol use or “failure” of field tests would supply.

In an “ordinary” DUI pull over, all the officer has is the three standard indicators that almost every DUI stop lists: bloodshot eyes, a strong odor of alcohol, and slurred speech.

There are plenty of reasons you might have these without having had a drink.  Unless you admit to drinking, “fail” field sobriety testing (in the judgment of the officer), or “fail” breath testing on the commonly uncalibrated and dirty portable breathalyzer, the reasonableness of the officer’s decision to arrest you for suspicion of DUI and compel you to submit to post-arrest chemical testing of your blood or breath becomes an issue that can be called into question at a suppression hearing or trial.  If you make admissions or submit to testing that isn’t required, the ability to raise that reasonableness-of-suspicion issue all but disappears.

When an officer asks about intoxication or requests/coerces you to perform field sobriety testing, you aren’t being offered a chance to demonstrate your sobriety, you are being “offered” a chance to make the case against you stronger.   That chance to make the case against you stronger is all I am suggesting that you refuse.

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Business Realities of the DUI Industry: A Problem of Supply and Demand

There is a massive industry that has arisen around what we commonly refer to as DUI cases.  Here in Pennsylvania, the average first time DUI offender pays around $1,900 in legal fees and then $4,000 to $6,000 in court costs, fines, fees, and the like. DUI is the most common crime in Pennsylvania with 43,365 people being charged with DUI in 2016, roughly equating to a quarter billion dollar industry in just one state.  

And it is a very profitable industry.

The DUI industry has no price competition, no inventory costs, and no marketing costs.  People who fall into the clutches of the DUI industry are simply ordered to pay the fees, there is no negotiating, no shopping around, and if you fail to pay, you will be sent to prison.

As good and just as it sounds, the industry has a problem, and that problem is supply and demand.  

Owing largely to public relations campaigns stigmatizing drunk drivers and the fear of falling afoul of the law, more and more drivers are taking an Uber, using a designated driver, using public transport, or not drinking outside the home.  This represents a reduced supply of “drunk drivers” for the DUI industry to extract money from.

Of course, that quarter billion dollar gravy train has a lot of mouths to feed.  The last thing anyone who makes a living off of DUI cases wants to see is an end to people driving drunk.  If anything, the industry wants more DUI cases in the system because that is the only way anyone in the industry could ever see a raise.

But the number of people who get behind the wheel drunk or in an outrageously impaired state has been declining for years, since the late 1930’s when the first modern scientific DUI laws imposed the then legal BAC limit of 0.15.

The Solution?  Move the Goal Posts.

The solution?  Increase the supply of people to run through the system by changing the definition of DUI to include more people, including people who might not even suspect that they are breaking the law.

If you are old enough to remember it, the crime was originally called ”Driving While Intoxicated.”  They really meant it, you had to be Intoxicated, or “drunk” to run afoul of the law.  

As the driving public came into compliance, the industry dealt with the dwindling supply of offenders by changing the crime to “Driving Under the Influence.”  You no longer had to be “intoxicated,” or “drunk,” just Influenced.  They solved the supply and demand problem by simply lowering the amount of alcohol you could have in your system.  It is around this time that the legal BAC limit in most states was lowered from .15 to .10.

Another Solution: Punish Sober Drivers

About 15 years ago, the industry again ran into a supply and demand problem.  It must have been bad because they wrote one heck of a new law.

This time the law was called “Driving After Imbibing Alcohol or Utilizing Drugs.”  

You no longer have to be “intoxicated.”  You don’t even have to be “influenced” at all.  You just have to be driving, “after” imbibing alcohol or using drugs.  In many cases, you can be stone cold sober and still be found guilty.

This new law again lowered the BAC ”limit,” this time to .08, and included “drugged” driving for the first time.

Some of the more interesting and perhaps ill-considered features of the new Driving after Imbibing (“DAI”) law, included that:

  • You would be guilty, as the highest rate offender, if a blood test showed you had the metabolites of an illegal or un-prescribed drug, even if you were demonstrably “sober” at the time of the pullover.
  • You would be guilty if at any point within two hours after driving a blood test showed a BAC in excess of .08.

The metabolites rule of §3802(d)(1)(iii) in PA Title 75 works to criminalize driving by people who may, in fact, be sober but who may have used illegal or un-prescribed drugs in the past.  This law works particular injustice on people who use marijuana, the metabolites of which can remain in the user’s blood for up to thirty days.  

Imagine a situation today where a driver goes to another country or jurisdiction where marijuana is legal, or even medically prescribed, and uses marijuana.  That person is subject to a DAI arrest and conviction, any time he or she drives, for up to thirty days after sobering up.

I have seen many, many very bewildered clients who didn’t understand how they were being charged with a “DUI” when they don’t drink at all and had shared a single a “joint” with a friend a week before the pullover.

The two-hour rule is also used in some unusual ways.  

Imagine a situation where you have dinner and drinks at a restaurant near your home.  The food in your stomach slows the absorption of alcohol through your stomach into your bloodstream, so in spite of the fact that you have had more than the recommended number of drinks, the alcohol hasn’t hit your blood or your brain yet.  

You are, at this point, legally sober, and will be for a while, certainly long enough to get home (depending on distance), so you get in your car and start driving.

On the way home, you make a less-than-complete stop at a stop sign.  The police pull you over and ask if you have been drinking. You admit drinking and pass the field sobriety tests.  The portable breathalyzer reveals a BAC of .04, which is under the legal limit.

I have handled cases that mirror this imaginary situation. In many, the officer has made people wait before allowing them to leave the scene of the pullover.  

The officer can make you wait up to two hours, during which time the alcohol in your stomach can start passing into your bloodstream and your BAC will start to climb.  If it goes over the .08 threshold at any time within two hours after driving you are retroactively guilty of DUI, despite the fact that if you hadn’t been pulled over, you would have been safely home while still under the legal limit.

It is interesting to note that both drivers in the above two scenarios were and felt “sober” but were found guilty nonetheless.  The marijuana smoker because of their use of marijuana in the past, and the restaurant diner because they would go over the legal BAC limit in the future.

Trick them with the BAC “Limit”

The newest trick that has come into use is the cynical and misleading use of our “general impairment” law:

  • “An individual may not drive, operate or be in actual physical control of the movement of a vehicle after imbibing a sufficient amount of alcohol such that the individual is rendered incapable of safely driving, operating or being in actual physical control of the movement of the vehicle.”

This is the carrying forward of a law that existed prior to the use of BAC standards and it relied on the officer’s subjective observation that the driver was so inebriated that they were a risk of harm to society.  These were people that showed obvious signs of their state, such as vomiting or the inability to stand up or walk straight.

The introduction of the use of BAC levels came about because it was thought, primarily by the insurance companies who had to pay for accidents, that there were levels of alcohol use that might not be easily identified by police as dangerous but which, nonetheless, were in fact dangerous.  

BAC levels were envisioned as levels of intoxication lower than that enjoyed by the obviously intoxicated driver, which still presented a risk of car crashes and other accidents.

As noted above, the current .08 BAC limit is actually the third BAC limit that the government has used.  If .08 is an accurate assessment of the BAC level beyond which drivers are incapable of safely driving, it stands to reason that the earlier limits, .15 and .10, were mistakes.  One might reasonably question the government’s ability to set any standard with authority, having already gotten it wrong twice.

The perspective of this blog, however, is that the BAC limit is being lowered to pull in more people, not because of scientific advances in the understanding of the effects of alcohol on coordination and driving skills.

It appears that even this third try at setting a BAC limit does not appear to be bringing in enough DAI cases.  I suggest this is the case because police and DA’s are, at this moment, prosecuting people every day for DAI with BAC’s lower than the .08 limit.

You might ask, how and why that is happening?

After all, the government has gone to great lengths to make the public aware of the .08 BAC limit.  The government prints and distributes charts showing how many drinks you can have based on your weight and still be under .08.  The government also approves courses and driver education programs publicizing the .08 limit.

A legal limit is something you can’t go over without breaking the law, for example, hunters are limited to three shells in their shotgun during hunting season. Imagine the game warden citing, and the DA prosecuting someone, with only two shells in their shotgun for having more than three.

The “how” of prosecuting people for DAI who have less than the legal limit of .08 BAC is accomplished by citing them under the old “general impairment” statute of §3082(a)(1) of PA Title 75, instead of the .08 limit of §3802(a)(2).  The police simply assume that, based on their training and observations, you were under the influence of alcohol to such degree that you were incapable of safe driving. Under the general impairment rule, your BAC is irrelevant.

As for the “why” of prosecuting people who are in compliance with the law, it could be that the driver in question actually was incapable of safe driving at some BAC under .08.  It could be that the driver in question “mouthed off” to the police.

Or it could simply be the law of supply and demand.