People v. Plank, 106 N.E.3d 995

Officer observed John Plank riding a motorized bicycle at ~26 mph; Plank admitted his driver’s license was revoked.
State charged Plank with driving a motor vehicle with a revoked license; charge elevated to a Class 4 felony based on his prior DUI and subsequent convictions.
Illinois Vehicle Code excludes “low-speed gas bicycle” from the definition of “motor vehicle” and defines it as a 2- or 3‑wheeled device with pedals and a gasoline motor <1 HP whose maximum speed on a paved level surface, when powered solely by the motor while ridden by an operator who weighs 170 pounds, is <20 mph. 625 ILCS 5/1-140.15; 1-146; 6-303(a).
Plank moved to dismiss, arguing the statutory definition is unconstitutionally vague (fails to give fair notice and invites arbitrary enforcement); the Douglas County circuit court agreed and dismissed the charge, declaring §1‑140.15 facially unconstitutional.
Illinois Supreme Court granted review and reversed, holding the statutory definition provides adequate standards for notice and enforcement and remanded for further proceedings.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether the Vehicle Code’s definition of “low-speed gas bicycle” is unconstitutionally vague under the federal and state due process clauses	State: definition supplies objective criteria (speed, engine power) and is enforceable	Plank: definition is vague because it hinges on driver weight (170 lbs), "paved level surface," and requires impractical determinations by officers; thus gives inadequate notice and invites arbitrary enforcement	Court: definition is not vague; it gives definite, objective criteria (engine capability measured by max speed under specified test conditions) and is enforceable; reversal and remand

City of Chicago v. Morales, 527 U.S. 41 (1999) (describing vagueness standards: notice and prevention of arbitrary enforcement)
United States v. L. Cohen Grocery Co., 255 U.S. 81 (1921) (statute using terms like “unjust or unreasonable” held vague)
Coates v. City of Cincinnati, 402 U.S. 611 (1971) (ordinance prohibiting “annoying” conduct held vague)
Boyce Motor Lines, Inc. v. United States, 342 U.S. 337 (1952) (risk falls on those who go near proscribed conduct)
United States v. Williams, 553 U.S. 285 (2008) (vagueness turns on indeterminacy of the prohibited fact)
Holder v. Humanitarian Law Project, 561 U.S. 1 (2010) (distinguishing vague statutes from those with objective standards)
Burg v. Municipal Court, 673 P.2d 732 (Cal. 1983) (upholding bright-line BAC limit despite practical testing limits)
People v. Falbe, 189 Ill. 2d 635 (2000) (upholding distance-based enhanced penalties as measurement rules)
People v. Fabing, 143 Ill. 2d 48 (1991) (statute invalid only if it provides no standard of conduct)
People v. Wear, 229 Ill. 2d 545 (2008) (probable cause may be supported by observable indicia of impairment)