Colorado drugged driving prevalence and impaired driving conviction rates: Effects of impaired driving definitions and a 5-nanogram limit for delta-9 tetrahydrocannabinol

Figures & data

Table 1. Colorado impaired driving misdemeanor offenses.

	DUI	DWAI
Description	Driving Under the Influence	Driving While Ability Impaired
Definition	Incapable of safe driving	Impaired to the slightest degree
Alcohol legal limits	≥.08 gm/dL per se	.05 gm/dL permissible inference
THC legal limits	≥ 5 ng/mL permissible inference	N/A

Colorado Revised Statute 42-4-4301.

Table 2. Changes in reported drug prevalence as a function of testing policies.

		2018	2019	2020
Test protocol	% drug and alcohol tested	7	20	37
	% alcohol tested only	51	40	22
	% drug tested only	5	2	0
Positive test results	% alcohol only	75.3	73.7	59.2
	% THC only	6.4	5.7	6.7
	% Other single drug	2.7	1.9	3.2
	% Polydrug	14.5	17.0	29.3

(Rosenthal and Reed 2023 Figure 9, Table 21).

Table 3. DUI case filings in 2020 by drug category.

	All tests		Full drug tests
Drug category	Number	%	Number	%
None detected	205	1.6%	183	2.4%
Alcohol only	7,360	59.2%	2,647	34.4%
THC only	831	6.7%	831	10.8%
Single other drug	398	3.2%	398	5.2%
Polydrug	3,646	29.3%	3,646	47.3%
Alcohol + THC	1,471	11.8%	1,471	19.1%
Alcohol + other	842	6.8%	842	10.9%
THC + other	556	4.5%	556	7.2%
Alcohol + THC + other	499	4.0%	499	6.5%
Polydrug not alcohol or THC	278	2.2%	278	3.6%
Total	12,440		7,705

“All tests” include CBI, CDPHE, and Den data (Rosenthal and Reed 2023, Table 21).

Of the 12,440 cases, 7,705 were tested for alcohol and other drugs, and 4,735 were tested for alcohol only. “Full drug tests” include CBI data only, were tested for both drugs and alcohol, and were provided by the Department of Public Safety under an Open Records Act request.

Table 4. Convictions and conviction rates by impairing substances identified.

	2018		2019		2020
Cause	Nbr	%	Nbr	%	Nbr	%
Overall	13,964	91%	14,440	92%	9,475	88%
Alcohol only	11,775	92%	11,792	93%	6,653	92%
Polydrug	2,239	91%	2,722	91%	3,029	90%
THC only	978	76%	907	78%	700	72%
Other single drug	410	80%	300	81%	302	77%

Convictions are judicial outcomes of either guilty, deferred, or deferred dismissed for either DUI or DWAI. Alcohol only conviction rates are based on all laboratory assays, including those that did not test for other drugs. (Rosenthal and Reed 2023 Table 35).

Table 5. Conviction rates for alcohol and THC by legal limits.

Drug Drug Level		2018	2019	2020	Average
Alcohol only	BAC .08+	95%	96%	95%	95%
Alcohol only	BAC .05-.079	76%	79%	75%	77%
THC only	5-ng+	89%	89%	83%	87%
THC only	< 5-ng	36%	39%	33%	36%

Conviction rates are based on convictions of either DUI or DWAI. (Rosenthal and Reed 2023, Appendices I & J).

Table 6. Conviction rates for alcohol and THC by offense.

Drug Offense		2018	2019	2020	Average
Alcohol only	DUI	91%	91%	90%	91%
Alcohol only	DWAI	97%	98%	97%	97%
THC only	DUI	46%	51%	42%	46%
THC only	DWAI	98%	98%	100%	99%
Polydrug w/ THC	DUI	86%	79%	87%	84%
Polydrug w/ THC	DWAI	100%	100%	100%	100%

(Rosenthal and Reed 2023, Appendices I & J).

Table 7. Convictions (nbr) and conviction rate (CR) by drug, concentration and offense.

		2018		2019		2020		3 yr Avg CR
	Charge	Nbr	CR	Nbr	CR	Nbr	CR
THC only	DUI THC 5-ng+	172	69%	155	70%	117	57%	65%
	DUI THC< 5-ng	13	8%	8	8%	11	11%	9%
	DWAI 5-ng+	444	99%	370	99%	312	100%	99%
	DWAI < 5-ng	70	93%	52	93%	35	97%	94%
Alcohol only	DUI BAC .08+	4,924	92%	5,032	93%	3,125	91%	92%
	DUI BAC .05-.079	34	29%	24	26%	22	29%	28%
	DWAI BAC 08+	3,565	100%	4,094	100%	2,382	100%	100%
	DWAI BAC .05-079	625	84%	670	85%	353	83%	84%

(Rosenthal and Reed 2023, Appendices I & J).

Rosenthal A, Reed J. 2023. Driving under the influence of drugs and alcohol. Colorado Department of Criminal Justice.

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