Traffic stops and DUI

The most frequent line on a Montana blotter is a traffic stop. Across 56 counties the volume is uneven, but the legal rules are statewide. This chapter walks through why you can be stopped, what implied consent really does, what field sobriety testing means, and what happens to your license afterward.

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What this chapter covers

• Why a Montana officer may pull you over (and why they do not need very much)
• What "reasonable suspicion" means at a traffic stop versus a Terry stop
• The implied consent law: MCA § 61-8-402
• Field sobriety tests, the preliminary breath test, and the 10-minute rule
• What happens to your license after a DUI arrest
• The administrative per se process and how to request a hearing
• Open container, passenger rights, recording the stop

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> Not legal advice. This chapter summarizes published Montana law in the Montana Code Annotated (MCA). Statutes change. Verify every citation against the current text at leg.mt.gov/bills/mca and consult a licensed Montana attorney for your specific situation.

> Editorial standards. Every claim links to a primary Montana Code section on leg.mt.gov/bills/mca. We do not invent scenarios or dispositions. If a citation has drifted from the current statute, email records@montanablotter.com — subject line Course Citation Update.

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Why you can be pulled over

The constitutional minimum is the same standard as a Terry stop: reasonable suspicion, supported by specific and articulable facts, that you are committing or have committed a traffic violation. (Whren v. United States, 517 U.S. 806 (1996); MCA § 46-5-401.)

Reasonable suspicion is a low bar. A single observed violation is enough:

• Speeding or driving too slowly (MCA § 61-8-303)
• Failure to signal (MCA § 61-8-343)
• Weaving within a lane (MCA § 61-8-301 covers reckless driving; lane-weaving alone may or may not meet the reckless standard)
• Equipment violation — a burned-out tail light is enough (MCA Title 61, Chapter 9)
• Expired registration (MCA § 61-3-301)

What an officer may not do is stop you on a pretext that is actually a search for criminal evidence. The U.S. Supreme Court in Whren held that an officer's subjective intent does not invalidate an objectively reasonable traffic stop. This means a stop made in order to investigate something else is still valid if a traffic violation actually occurred. It does not mean the stop is valid if no violation occurred — the test remains objective.

Sobriety checkpoints

DUI checkpoints are addressed in State v. Walser, 2014 MT 167, where the Montana Supreme Court reaffirmed that checkpoint stops must satisfy Fourth Amendment and Article II, Section 11 standards. Operational plan requirements include neutral criteria for stopping vehicles, advance publicity, and supervision by a commanding officer. Random stops without a plan are unconstitutional in Montana.

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What happens during the stop

The three phases

1. Approach. The officer approaches the vehicle. You are being detained. Stay in the car unless told otherwise. Turn off the engine. Roll the window down far enough to communicate, but no further than needed.
2. Investigation. The officer will ask for license, registration, and insurance (MCA § 61-8-301 and related). You are required to produce these. If you cannot, the officer may give you a reasonable opportunity to locate them.
3. Decision. The officer either writes a citation, gives a warning, or escalates to a DUI investigation.

What you must produce

You must produce, on request:

• Driver's license. Carry it. MCA § 61-5-114 (display on demand).
• Registration. MCA § 61-3-101.
• Proof of insurance. MCA § 61-6-301 requires liability coverage; MCA § 61-6-304 requires proof.

What you may decline

• Answering questions beyond identity and documents. Once the documents are produced, you may decline to answer where you are going, where you have been, or whether you have been drinking. The answers are admissible against you; the silence is not.
• Consenting to a search of the car. The car is a different constitutional category than the home. Under the automobile exception, an officer may search the car without a warrant if they have probable cause to believe it contains evidence of a crime (Carroll v. United States, 267 U.S. 132 (1925)). Without probable cause, the officer needs consent or a warrant. The phrase "I do not consent to a search" is the correct answer.

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Implied consent and the 10-minute rule

What "implied consent" really means

By operating a motor vehicle on a Montana public highway, you are deemed to have consented to a chemical test of your blood, breath, or urine if an officer has reasonable grounds to believe you are under the influence. MCA § 61-8-402. The statute is straightforward; the consequences are not.

Implied consent does not mean you have consented. It means the law has created a penalty for refusing. The penalty is administrative: the Montana Department of Justice will suspend your driving privilege. The criminal penalty for DUI (MCA § 61-8-401) is unaffected by whether you take the test.

What an officer must do before asking

Before requesting a breath or blood test, the officer must:

1. Have reasonable grounds to believe you are under the influence.
2. Place you under arrest for DUI.
3. Inform you of the implied consent advisory — a specific, statutorily-prescribed warning that includes the consequences of refusal.

The advisory language is set out in MCA § 61-8-402(3). If the advisory is not read correctly, the refusal (or the result) may be challenged.

The 10-minute rule

Montana v. their admin rule at ARM 23.4.201 (administrative rules of Montana) and the Montana Supreme Court's interpretation in State v. Pendergrass require that the implied consent advisory be given and a decision reached within a timeframe that protects the driver's rights. The well-known "10-minute rule" is shorthand for the rule that an officer may not delay the advisory process to obtain a refusal. The case is regularly cited; verify the citation in current Montana case law before relying on it.

This is one of the more often-litigated corners of Montana DUI law. If you are facing a refusal-based suspension, the public defender's office or a private DUI attorney will know the current state of the 10-minute rule.

What happens if you refuse

Refusal triggers an administrative suspension of your license:

• First refusal: 6-month suspension, with restricted driving privilege available after 30 days for work/school/medical (MCA § 61-8-403).
• Second refusal within 5 years: 1-year suspension, no restricted privilege during the suspension.
• Third or subsequent refusal: 1-year suspension.

You have the right to request an administrative hearing within 10 days of the notice of suspension (MCA § 61-8-403(2)).

What happens if you take the test and the result is 0.08 or higher

A test result of 0.08 BAC or higher creates a rebuttable presumption that you were under the influence (MCA § 61-8-401(2)). The criminal case proceeds independently of the administrative per se suspension.

What happens if you take the test and the result is below 0.08

You may still be charged with DUI under the "under the influence" prong, which is not strictly BAC-based (MCA § 61-8-401(1)(a)). A low BAC result is evidence in your favor, but not a shield.

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Field sobriety tests

The standardized field sobriety tests (SFSTs) — walk-and-turn, one-leg stand, horizontal gaze nystagmus — are voluntary in Montana. The officer may ask; you may decline. Refusal of field tests cannot be used against you in the criminal case (South Dakota v. Neville addressed refusal of the chemical test, not the SFSTs, and the SFSTs are not addressed by Montana's implied consent statute).

Practical reality: SFSTs are designed to be administered under conditions favorable to the officer. Roadside surfaces are uneven, weather is cold, the driver is nervous, and officers are trained to interpret any deviation as a "clue." A defense attorney will look at the dashcam video, the weather, and the officer's training record. None of this is dispositive, but it is the texture of these cases.

The preliminary breath test (PBT) — the small handheld device offered roadside — is a separate question. Under MCA § 61-8-405, the PBT result is not admissible in the criminal case. It may be used by the officer as part of deciding whether to make a DUI arrest. You may decline the PBT.

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Search of the car

The trunk

The trunk is not categorically protected. An officer with probable cause may search the entire vehicle, including the trunk and any containers inside (United States v. Ross, 456 U.S. 798 (1982)). Without probable cause, the officer needs consent or a warrant. Containers and bags inside the car generally receive less protection than containers inside a home.

Passengers

Passengers have a limited privacy interest in the car. They may be asked to identify themselves and may be detained briefly. A passenger's refusal to identify may be charged under MCA § 45-5-401. A passenger's belongings are subject to the same probable-cause rule as the driver's.

Open container

Open container — MCA § 61-8-460 — prohibits an open container of alcohol in the passenger area of a motor vehicle on a highway. A first offense is a misdemeanor with a fine. The statute has exceptions for the trunk and for the area behind the last upright seat in a vehicle without a trunk. Beer cans, half-empty bottles, and empties can all be relevant depending on context.

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After the stop: citation, arrest, or warning

• Citation. You are released. The case proceeds in court. You are required to respond to the citation by the date on it. Failure to appear can lead to a bench warrant (MCA § 46-6-212).
• Warning. No legal consequence. A record may be kept by the agency.
• Arrest. You are transported, booked, and either released on bond, released on your own recognizance, or held pending arraignment. Chapter 5 covers this.

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What you can do tonight

• [ ] Confirm your insurance card is in the car. MCA § 61-6-301.
• [ ] Check your registration expiration. MCA § 61-3-301.
• [ ] Know the Montana State Highway Patrol non-emergency line for your area.
• [ ] Read the implied consent statute end-to-end. It is short and the language matters: MCA § 61-8-402.
• [ ] Find a public defender contact in your county before you ever need one.

Where to verify

• MCA Title 61 — Motor Vehicles
• MCA § 61-8-401 — DUI definitions and penalties
• MCA § 61-8-402 — Implied consent
• MCA § 61-8-403 — Suspension upon refusal
• MCA § 61-8-405 — Preliminary breath test
• MCA § 61-8-460 — Open container
• MCA § 61-6-301 — Liability insurance required
• Whren v. United States, 517 U.S. 806 (1996)
• Carroll v. United States, 267 U.S. 132 (1925)

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Chapter last reviewed: 2026-08-05 · Montana Blotter · Know Your Rights course