State v. Ivan Drake Pettit, 162 Idaho 849

Background

On May 20, 2015, an officer stopped Ivan Pettit for failing to use a right-turn signal while curving right through an intersection in Moscow, Idaho; the stop led to DUI (second offense) and driving without privileges charges.
The intersection has three southbound lanes: left lane for straight/left turns (to Highway 8 East or Highway 95 North/8 North) and center/right lanes guiding vehicles to curve right and continue on Highway 95 South; signage and right-turn arrows were present.
Pettit was in the center lane, faced a green right-turn arrow, and curved right without signaling; the officer stopped him for failing to signal.
Pettit moved to suppress evidence, arguing no statutory duty to signal under I.C. § 49-808(1); the magistrate granted suppression, finding no signal required and that the officer’s legal mistake was not reasonable (also alternatively finding vagueness).
The district court affirmed the magistrate on grounds that Pettit was not required to signal; this appeal followed.

Issues

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether I.C. § 49-808(1) required Pettit to signal when curving right through the intersection	§ 49-808(1) unambiguously requires a signal because Pettit turned "onto" a (new) highway	Pettit remained on the same highway (Highway 95 South) — he did not turn onto a new highway, so no signal required	Held: Pettit did not turn onto a new highway; statute did not require a signal, so officer lacked reasonable suspicion to stop
Whether the officer’s mistake of law was objectively reasonable	Stop was lawful; statute plainly required signaling in these circumstances	Even if statute ambiguous, the officer might be wrong but potentially reasonable given intersection characteristics	Held: The officer’s mistake was objectively reasonable because the start/end of a “highway” at the intersection is debatable
Whether an objectively reasonable mistake of law precludes suppression under Idaho law	Heien (U.S. Supreme Court) supports treating reasonable mistakes of law like reasonable mistakes of fact — so evidence should not be suppressed	Idaho Constitution (Article 1, § 17) and Idaho precedent reject a good-faith exception; suppression still required	Held: Idaho’s independent exclusionary rule controls; even an objectively reasonable mistake of law does not avoid suppression
Whether court needed to resolve statute vagueness as applied	State: statute not unconstitutionally vague as applied	Pettit: alternatively statute is vague as applied	Held: Court did not reach vagueness because plain-text interpretation resolved the case (no signal required)

Key Cases Cited

Delaware v. Prouse, 440 U.S. 648 (Fourth Amendment reasonableness of vehicle stops)
United States v. Cortez, 449 U.S. 411 (reasonable-suspicion totality-of-circumstances)
Heien v. North Carolina, 135 S. Ct. 530 (reasonable mistake of law may justify stop under Fourth Amendment)
Michigan v. DeFillippo, 443 U.S. 31 (good-faith reliance on statute later declared void)
State v. Guzman, 122 Idaho 981 (Idaho rejects good-faith exception under Article 1, § 17)
State v. Koivu, 152 Idaho 511 (reaffirming Guzman and Idaho’s independent exclusionary rule)
State v. McCarthy, 133 Idaho 119 (objective-reasonableness inquiry for officer’s mistake of law)
Verska v. Saint Alphonsus Reg'l Med. Ctr., 151 Idaho 889 (statutory-interpretation directive cited by the court)