Over 40% of deceased drivers in vehicle crashes test positive for THC: Study

Original Article ↗ Hacker News Discussion ↗

Study design, scope, and limitations

  • Data come from 246 deceased drivers in a single Ohio county (Montgomery) whose autopsies included THC testing; only an abstract is available, not a full peer‑reviewed paper.
  • Commenters question:
    • Whether all driver fatalities were autopsied and tested or only those with suspected drug use (selection bias).
    • Use of the mean THC level (30.7 ng/mL) without a distribution or median; a few extreme cases could inflate the average.
    • Lack of accompanying data on alcohol and other drugs, seatbelt use, fault in the crash, or age distribution.
  • Several note the headline and press framing are stronger than what the limited data can justify.

Correlation vs causation and missing baselines

  • Many stress that “THC present in blood” ≠ “crash caused by THC.”
  • Key missing context:
    • What share of all drivers (or all people) would test positive for THC at similar thresholds?
    • How THC prevalence among deceased drivers compares to non‑fatal crash drivers or to the general driving population.
  • Some cite surveys where ~20% report any cannabis use in the past year, arguing 40% at impairment thresholds among dead drivers is “stunning”; others reply that self‑report is undercounted and demographics (young, male, night driving) confound this.

Impairment, thresholds, and biology

  • Strong debate over whether blood THC concentration is a reliable impairment proxy:
    • THC and its metabolites persist long after subjective sobriety, especially in habitual users.
    • Legal limits (2–5 ng/mL in many jurisdictions) may criminalize frequent users who are not acutely high.
  • Others counter that very high levels (tens of ng/mL) likely reflect recent use, not just residue, and that cannabis impairs reaction time and complex tasks, even if users “feel fine.”

Effect of legalization

  • A central finding—THC‑positive rate among deceased drivers did not change meaningfully before vs. after Ohio legalization—surprises many.
  • Competing interpretations:
    • Legal status doesn’t strongly change who chooses to drive high (supply already abundant pre‑legalization).
    • Or overall use rose, but high‑and‑driving behavior did not.
    • Some see this as further evidence that criminalization alone doesn’t reduce risk.

Driving behavior, enforcement, and policy

  • Numerous anecdotes across US cities of:
    • Drivers openly smoking/vaping in cars.
    • Post‑COVID increases in reckless driving (speeding, red‑light running, wrong‑way driving), often attributed more to lax enforcement and “lawlessness” than to THC per se.
  • Some argue for much tougher, escalating penalties (including jail and long‑term license loss) for any impaired driving; others point to the failures of the “war on drugs,” racial disparities, and existing over‑incarceration.
  • Broad agreement that:
    • Texting and general distraction are major, often under‑punished risks.
    • We lack a THC equivalent of BAC: an objective, time‑linked impairment test.
    • Road design, enforcement consistency, and seatbelt use remain huge, under-discussed determinants of fatalities.

Attitudes toward cannabis and normalization

  • Several commenters see the 40% figure as evidence cannabis harms similar to alcohol and criticize cultural minimization of “stoned driving.”
  • Others emphasize that:
    • Normalization and legalization shouldn’t mean ignoring risk.
    • Solid policy requires separating “presence” from “impairment” and accounting for confounders before drawing strong causal claims from this single, limited dataset.