Yes, a report from another driver, a bartender, or a family member can justify a traffic stop in Montana, but only if the report is reliable enough. The Montana Supreme Court uses a three-part test, and it has thrown out stops where an anonymous caller offered an opinion and nothing else. This page explains the test and how the cases have come out. It is part of our Montana DUI Guide.
A Tip Has to Add Up to Particularized Suspicion
The standard for any stop is the same. An officer needs particularized suspicion that someone in the vehicle has committed, is committing, or is about to commit an offense (MCA § 46-5-401(1)). Our page on the reasons police can stop you covers stops based on what the officer personally sees.
A tip is different because the officer is relying on someone else's eyes. In State v. Pratt, 286 Mont. 156, 951 P.2d 37 (1997), the Court held that information from a citizen informant, whether identified or anonymous, may provide the basis for a stop, but the report must carry some indication of reliability. Less reliable tips require more corroboration by the officer.
The Three Pratt Factors
| Factor | Why it matters | What satisfies it |
|---|---|---|
| 1. Did the caller identify themselves? | A caller who gives a name, or reports in person, is exposed to liability if the report is false. That makes the tip more reliable. | A name, address or phone number given to dispatch. An anonymous call scores low here. |
| 2. Is the report based on personal observation? | An officer may infer personal observation when the report has enough detail that it was plainly not made up. | A description of the driving or the drinking the caller saw, plus the vehicle, plate and direction of travel. |
| 3. Did the officer corroborate it? | Corroboration happens when the officer sees illegal activity, or finds the person and vehicle substantially as described. | For a reliable tip, finding the described vehicle where the caller said it would be can be enough. |
The factors are weighed together under the totality of the circumstances. A strong showing on the first two lowers what the officer has to confirm personally.
Tips That Justified the Stop
- Pratt (1997). The night manager of a convenience store called 911, gave his name, and reported a customer he believed was intoxicated, with the vehicle, its personalized plate, and its direction. An officer found the vehicle almost immediately on the street described. The stop was lawful even though the officer saw no bad driving.
- State v. Rutherford, 2009 MT 154. A passenger in another car gave dispatch her full name and cell number and described a truck swerving across the center line and fog line, speeding up and slowing down, and flashing its lights, over about 12 minutes. The deputy found a truck matching the description in the place and direction reported. All three factors were met.
- City of Missoula v. Moore, 2011 MT 61. A friend called 911 to say the driver had just left her home upset after having "a lot to drink," and described the vehicle and its route. The Court held the report was based on the caller's own observation of the driver minutes earlier and was more than a bare opinion.
Tips That Did Not
- State v. Lee, 282 Mont. 391 (1997). An anonymous caller said she believed a named driver was under the influence and speeding, and described his car and direction. She gave no basis for the belief. The officer found the car traveling under the speed limit and saw no erratic driving. The Court held the caller's information alone, with no other objective data, did not support a stop, and ordered the case dismissed.
- State v. Lafferty, 1998 MT 247. An anonymous caller reported a drunk driver and gave a vehicle description and partial plate, with no particulars about the driving. The trooper found the pickup and saw it cross the fog line twice. Because the tip was anonymous and unsupported, the trooper needed to see driving that was illegal or indicative of impairment, and the Court held that those fog line crossings were neither. The DUI was ordered dismissed.
The pattern is consistent. Finding the car is enough to corroborate a detailed report from an identified caller. It is not enough to rescue an anonymous opinion.
What Dispatch Knew Counts Too
Officers usually hear a shortened version of the call over the radio. Montana courts do not limit the analysis to that summary. In applying the test to a tip relayed by dispatch, the Court looks beyond what was given to the officer to include what the dispatcher knew (Rutherford; Moore). Pratt also held that the officer making the stop does not have to assess the caller personally first.
That cuts both ways. It means a stop can be upheld on details the officer never heard. It also means the recording of the call is central evidence: if the caller was vaguer on the phone than the report suggests, that matters.
Reports After a Crash or After You Are Home
Calls about a collision, a car in a ditch, or a driver who has already gone home raise extra questions: who was driving, when, and whether officers may come to the door. Those are covered in arrested at home after driving. A call about someone asleep in a parked car is usually handled as a welfare check, which follows a different rule.
How a Tip-Based Stop Is Examined
In a case that began with a call, the review starts with the call itself:
- the 911 audio or transcript, and the dispatch log showing what was relayed and when;
- whether the caller gave a name and contact information;
- what the caller actually saw, as opposed to what they assumed or were told;
- what the officer observed before turning on the lights, and whether the video matches the report.
These records can be requested from the prosecutor (MCA § 46-15-322). If the tip and the officer's own observations do not add up to particularized suspicion, the remedy is a motion to suppress the evidence that followed (MCA § 46-13-302). See also challenging the traffic stop.
This page explains Montana law in general as of the 2025 Montana Code Annotated and the court decisions cited. It is not legal advice about your specific case.