State v. Larson, 2010 MT 236

Midnight traffic stop near South Ave and Reserve St; two deputies with light bars observed Larson’s driving behavior, including screeching tires and crossing the intersection; Larson's truck had oversized tires and no mud flaps; Larson presented slurred speech, slow responses, and admitted drinking earlier in the day; breath test yielded .023, raising suspicion of impairment; Larson retrieved marijuana and a pipe from his vehicle and admitted smoking; he was arrested for DUI and refused a blood test.
Pretrial suppression motion: Larson sought suppression of roadside statements and evidence; district court ruled there was particularized suspicion for the stop and for field sobriety testing, and that Miranda warnings were not required; evidence of marijuana was not unlawfully obtained,
Trial testimony included deputies’ lay observations regarding marijuana impairment; district court allowed their opinion testimony despite not being qualified experts; defense objected.
Jury instructions included a rebuttable inference that a refusal to submit to testing can support a finding of impairment; Larson proposed an enhanced instruction outlining that a refusal alone does not prove impairment and that corroborating evidence is required, which the district court declined.
On appeal, the Montana Supreme Court affirmed the conviction, addressing the sufficiency of suspicion, Miranda advisement, admissibility of expert opinion, and jury instruction issues.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Was there particularized suspicion to stop Larson's vehicle?	Larson argues no specific suspicion warranted the stop.	State argues observations plus mud-flap potential license a stop.	Yes; stop supported by totality of circumstances.
Was there particularized suspicion to conduct field sobriety tests?	Suspicion did not extend to field sobriety tests.	Investigative stop justified escalation to sobriety testing.	Yes; ongoing DUI investigation supported sobriety testing.
Were Miranda warnings required during roadside DUI investigation?	Detention exceeded permissible scope, triggering custodial interrogation and need for warnings.	Roadside Terry-like stop not custodial; warnings unnecessary.	No; detainment was temporary, routine, and noncustodial.
Did the district court err by admitting deputies' opinion testimony on marijuana impairment?	Opinions were lay or insufficiently foundational; should be excluded.	Opinions were admissible as lay/experiential testimony.	Error; foundation for expert testimony was insufficient.
Did the court abuse its discretion in not adopting Larson's jury instruction proposal?	Need explicit burden regarding corroborating evidence beyond the inference.	Instructions as a whole adequately informed jurors; no abuse.	No; instructions were proper when viewed as a whole.

Grinde v. State, 813 P.2d 473 (Mont. 1991) (particularized suspicion analysis under driving behavior observations)
Brown v. State, 203 P.3d 842 (Mont. 2009) (totality-of-the-circumstances standard for stops)
Hulse v. DOJ, Motor Vehicle Div., 961 P.2d 75 (Mont. 1998) (necessity of particularized suspicion for field sobriety testing)
Elison, 14 P.3d 456 (Mont. 2000) (roadside questioning analogous to Terry stop; no Miranda warnings required)
Nobach, 46 P.3d 618 (Mont. 2002) (lay vs. expert testimony on drug impairment; need for foundation under M.R. Evid. 702)
Michaud, 180 P.3d 636 (Mont. 2008) (explanation of corroborating evidence requirement for § 61-8-404)
Miller, 342 Mont. 244 (Mont. 2008) (lack of explicit ‘competent corroborating evidence’ instruction not reversible error)
Elison, 302 Mont. 228 (Mont. 2000) (roadside investigations not custodial if scope remains related to DUI)
State v. Stanczak, 232 P.3d 896 (Mont. 2010) (limits on interrogation during DUI stop)
State v. Nelson, 101 P.3d 261 (Mont. 2004) (reasonableness of roadside detention duration)