typewriter - guilty until proven innocent

Police stops, driving while impaired

Do not confess. Do not consent to searches.


This supplements Guilty until proven innocent (never plead guilty), Until proven innocent - the process, and Police stops. This describes police traffic stops targeting impaired driving.

These are general comments about US criminal process. Other countries of course have different requirements. This is particularly the case with impaired driving, because the US and a few other countries have probable cause requirements for requiring a chemical test for impairment. Without probable cause, the chemical test results cannot be introduced in a court of law under the Exclusionary Rule. ("probable cause" and "Exclusionary Rule" are US terms. Terms in other countries may differ.)

Not legal advice

This is also not legal advice; it is general commentary on the internet. For legal advice and information outside of the US, please look up local law or speak with a lawyer. If speaking with a lawyer is not an option, locate a civil rights organisation in your jurisdiction such as (in the US) the ACLU. There are also quite a few attorneys with information on webpages.

The laws and procedures vary between jurisdictions, so it makes sense to check with local sources (in person or on the web) for information in any given jurisdiction.

Impaired driving stops

US-centric - Police stop procedures for impaired driving (DUI, DWI, etc.) in the US and a few other countries follow a need to establish probable cause ("reasonable grounds" in Canada; not to be confused with "reasonable suspicion" in US law) in order to sustain a charge based on a mandatory chemical test. If probable cause (or the equivalent) is required, Field Sobriety Tests (FSTs or SFSTs) will be commonly used. If probable cause is not required, the police will not waste their own time with roadside "tests" or "examinations" that are basically pseudoscience.

As with any arrest, the procedure for an impaired driving stop follows a progression, necessary to establish probable cause, in this case, before requiring a chemical test. The following are the US terms:

  1. "Reasonable suspicion" (reason to stop a vehicle, not to be confused with "reasonable grounds" in Canada)
  2. "Probable cause" - This is probable cause for arrest, but is also necessary to establish a foundation for a required chemical test if the chemical test is to be used as evidence in a trial.
  3. An evidential test (breathalyzer, blood, urine, drug swab) Essentially the Implied Consent law requires either probable cause for arrest or a warrant because the chemical test is considered a "search incident to arrest".
  4. Formal charges

The actual terms (e.g., "arrest") will vary by jurisdiction, but the procedure is subject to Constitutional limits. It is possible to prosecute an impaired driving charge without a chemical test, but police will try to obtain the test (or an implied consent refusal).

Finding probable cause - Probable cause can include some external observations, but confessions, FSTs and Preliminary Breath Tests (PBTs) or Preliminary Alcohol Screening (PAS) tests make it far easier to document probable cause.

The difference between probable cause and evidence in court - Both are evidence, but probable cause does not need to meet the standards of proof to establish guilt "beyond a reasonable doubt". Instead, probable cause is just that -- probable cause. It allows the police to proceed with an implied consent request to require the chemical test. Without probable cause, the defendant's lawyer will have a strong case for excluding implied consent evidence according to something called the "Exclusionary Rule". These field observations, including FSTs (in some jurisdictions) can be used as evidence at trial, but that is really secondary to establishing probable cause.

The typical procedure comprises:

First try to obtain a confession. An admission of recent consumption of any alcohol will do. (e.g., "A couple of beer.", which is a sort of police joke)  If the driver made any statements about drinking alcohol or taking drugs (whether legal or illegal), this evidence can establish probable cause that the driver was under the influence. (Do not lie; just express a need to remain silent until speaking with a lawyer.)

Note that probable cause does not mean sufficent alcohol to demonstrate intoxication. In most cases, probable cause is evidence of any recent alcohol consumption.

Field Sobriety Tests (FSTs or SFSTs), "HGN first" - FSTs are the familiar roadside "monkey tricks" tests, and are entirely voluntary. Most lawyers in the field advise declining SFTs (starting with HGN !), and often describe their primary function as to collect bogus evidence. The NHTSB describes establishing probable cause.

Details of FSTs are found elsewhere (e.g., Wikipedia article on Field Sobriety Tests) The important aspect is that the Horizontal Gaze Nystagmus Test (HGN) is given fist.

The Horizontal Gaze Nystagmus Test (HGN) is a variation of the roadside "monkey tricks" tests. The HGM test is intended to track the suspect's eyes for visible nystagmus (non-smooth eye movement) at the periphery of vision. This requires that the suspect (voluntarily) track an object with the eyes. The procedure is to watch eye movement while the subject is tracking a moving object such as a pencil. Courts vary on whether this is a "scientific test", but this is a legal evidentiary definition. In either case, the HGN is valid to establish probable cause

HGN first - There are several reason for "HGN first"

Preliminary Breath Test (PBT) or Preliminary Alcohol Screening test (PAS) - This is the same technology as an evidential breath test, but does not follow formal procedures for evidential breath testing. The Preliminary Breath Test is used to establish probable cause for a DUI arrest and it is performed before a driver is arrested. Local recommendations from lawyers vary from never accept a PBT to only take a PBT with no recent alcohol, to only take the PBT if one knows one is below a "presumed sober" level (often different from the per se level; check local information on this one).

While a few jurisdictions mandate the PBT, the penalties are rarely, if ever, as severe as an implied consent refusal. (A PBT may be a requirement for drivers on probation.) Depending on the jurisdiction, any detected alcohol (beyond nominal levels) is probable cause for arrest. (In most cases, the police will state that a "low blow" will not result in an arrest, but that is often not true. Police are allowed to lie about this.)

Since the PBT is not part of the implied consent law, many attorneys recommend conditioning acceptance of a PBT on speaking to an attorney first. Most police will refuse, but the request to speak with an attorney or refusal on advice of an attorney demonstrates the suspect did not arbitrarily refuse. Some attorneys recommend accepting a PBT if the suspect had consumed no alcohol, but that recommendation varies widely between attorneys.

The evidential chemical test cannot be refused without criminal or pseudo-civil penalties. If there was no probable cause, that can be litigated after the fact to exclude the chemical tests under the Exclusionary Rule.

In many cases, it is likely that a suspect who refuses FSTs or PBTs will still be arrested. What is important is that an arrest without sufficient probable cause is far better than arrest with probable cause. It is also very likely that, if FSTs or PBTs are requested, the police have already determined to arrest the suspect.

In summary - Most attorneys recommend that a suspect not confess and recommend the suspect should politely refuse field tests.


Avoid unnecessary police encounters.
Regularly check the vehicle's lighting. Reflections are easy to check when bored at a stoplight.

Don't get careless at stop signs, lane changes, etc.

Be able to immediately retrive the vehicle's documentation.

Expect multiple simultaneous requests, or unexpected questions.

Leave the smart-ass stuff for "Sovereign Citizens" and other show-offs.
(... but enjoy their videos on YouTube.)

Other details

There are a number of details, which can be searched on the web. For example, most attorneys will state, if stopped for DUI, it is usually best refuse "field sobriety" tests.

Here's a Maryland Lawyer's Comments on refusing field sobriety or roadside "monkey tricks" tests.

If there is a legal requirement, be sure to state this clearly when the formal request is made.
In the above example, if one is willing to consent to a chemical test, state, "I will comply with a demand to take a chemical test if required." (or "I will take the 'evidence' test for blood alcohol if required.") That makes it difficult for the police to argue later that consent was refused as a matter of law by ambiguous actions on your part. Such claims of refusal are unlikely to stand up in court, but a statement makes things clear.

It is unlikely that police will disguise the Implied Consent request. In most states, there is a specified procedure used to demonstrate that the suspect is clearly informed that a request is made pursuant to the Informed Consent law. The police need to demonstrate in court that a clear Informed Consent request was made. What is far more likely is an implication or outright lie that something other than the chemiical required under the Informed Consent law is subject to informed consent.

If you have an invisible disability, state this to the police.
While there are a number of bullys on "the job", most police behaviour is based on training on how to make judgement calls. Letting the police know what to expect helps in these situations.

Do not physically resist.
There's plenty of time to deal with illegal police action later.

Never make any move such as touching a policeman without permission.

Do not argue with the cop.
There is plenty of time for that later, either in the courts, through a lawyer, or even with a visit to the police station.

Expect the police to ask "why"
Unless you can come up with a polite explanation, the best response is just a scripted answer, such as:
I wish to remain silent.
(same answer, regardless of the stage of the encounter)
I need to talk with a lawyer.
(same answer, regardless of the stage of the encounter)
Repeat of the original answer.
My [cousin, neighbour, dog, neighbour's dog, etc.] is an attorney. She told me to never consent to searches.
I call that the "some a**hole" answer - "Some a**hole told me to remain silent"

Maintain a regimented form of politeness.
It shows the officer that you are not confrontational (in a street sense) and that you are confident enough to stand up for your rights. Do not say "I have rights."

"For privacy" or "I understand, sir." are generally suitable answers.

Comment on driving while impaired

<lecture mode here> (sorry)

If you expect to be driving over the per se limit, you need to do more than learn how to avoid confessions or probable cause. For one thing, you will almost certainly give the police probable cause through your driving, or worse. Consider that developing a strategy for avoiding driving impaired is going to be a lot easier than a restricted license, license revocation, prison, expenses and more expenses from high insurance costs. Whether one has an alcohol problem or not is really up to the individual. The only issue with the law (for driving) is to do what is necessary to avoid what is prohibited, which is driving while impaired. You know this shit.

Along the same lines, the per se limit is just that -- a limit. It's a number and the number doesn't care how capable your are.

There are questions as to low levels (e.g., see Grand Rapids Effect (Wikipedia)), but it is clear that at most per se levels, an impaired driver is a serious hazard. Just don't do it, because it ain't worth it.

Also consider that, if the suspect has a history of impaired driving convictions, confession and probable cause evidence obtained in the field is more-or-less an afterthought. The police already have probable cause from police records of convictions, which are easily combined with observations not requiring confessions, FSTs or PSTs. At that point, the suspect must depend on the outcome of chemical test as required under the implied consent law.

I hadn't studied what the effects of cannabis on driving are, but it only makes sense to avoid being in a situation where one is obviously high and trying to convince the police that one is not. Again, just avoid putting yourself in that situation.

</lecture mode off>

More information

Police stops are described at

"busted" YouTube video
(45 minute video, but worth watching)

(same thing, in text)

The ACLU website

Please view one of these. In other words, Do not confess

back to arrest.html - Police stops
back to notguilty.html - Never plead guilty
to process.html - "Guilty until proven innocent" (the process)

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First written 2-Jun-18. Last revised 2 Jun 18. ~~ This page copyright 2018,
Stan Protigal - Comments about this site: email me

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