Simulated driving performance among daily and occasional cannabis users

OBJECTIVE

Daily cannabis users develop tolerance to some drug effects, but the extent to which this diminishes driving impairment is uncertain. This study compared the impact of acute cannabis use on driving performance in occasional and daily cannabis users using a driving simulator.

METHODS

We used a within-subjects design to observe driving performance in adults age 25 to 45 years with different cannabis use histories. Eighty-five participants (43 males, 42 females) were included in the final analysis: 24 occasional users (1 to 2 times per week), 31 daily users and 30 non-users. A car-based driving simulator (MiniSim™, National Advanced Driving Simulator) was used to obtain two measures of driving performance, standard deviation of lateral placement (SDLP) and speed relative to posted speed limit, in simulated urban driving scenarios at baseline and 30 min after a 15 min ad libitum cannabis smoking period. Participants smoked self-supplied cannabis flower product (15% to 30% tetrahydrocannabinol (THC). Blood samples were collected before and after smoking (30 min after the start of smoking). Non-users performed the same driving scenarios before and after an equivalent rest interval. Changes in driving performance were analyzed by repeated measures general linear models.

RESULTS

Mean whole blood THC cannabinoids concentrations post smoking were use THC = 6.4 ± 5.6 ng/ml, THC-COOH = 10.9 ± 8.79 ng/mL for occasional users and THC = 36.4 ± 37.4 ng/mL, THC-COOH = 98.1 ± 90.6 ng/mL for daily users. On a scale of 0 to 100, the mean post-use score of subjective high was similar in occasional users and daily users (52.4 and 47.2, respectively). In covariate-adjusted analysis, occasional users had a significant increase in SDLP in the straight road segment from pre to post compared to non-users; non-users decreased by a mean of 1.1 cm (25.5 cm to 24.4 cm) while occasional users increased by a mean of 1.9 cm (21.7 cm to 23.6 cm; p = 0.02). Daily users also increased adjusted SDLP in straight road segments from baseline to post-use (23.2 cm to 25.0 cm), but the change relative to non-users was not statistically significant (p = 0.08). The standardized mean difference in unadjusted SDLP from baseline to post-use in the straight road segments comparing occasional users to non-users was 0.64 (95% CI 0.09 - 1.19), a statistically significant moderate increase. When occasional users were contrasted with daily users, the baseline to post changes in SDLP were not statistically significant. Daily users exhibited a mean decrease in baseline to post-use adjusted speed in straight road segments of 1.16 mph; a significant change compared to slight speed increases in the non-users and occasional users (p = 0.02 and p = 0.01, respectively).

CONCLUSION

We observed a decrement in driving performance assessed by SDLP after acute cannabis smoking that was statistically significant only in the occasional users in comparison to the nonusers. Direct contrasts between the occasional users and daily users in SDLP were not statistically significant. Daily users drove slower after cannabis use as compared to the occasional use group and non-users. The study results do not conclusively establish that occasional users exhibit more driving impairment than daily users when both smoke cannabis ad libitum.

Safety analysis of work zone complexity with respect to driver characteristics - A simulator study employing performance and gaze measures

Driving is a complex task that consists of several physical (motor-related) and physiological (biological changes within the body) processes occurring simultaneously. The complexity of the task depends on several factors, but this research focuses on work zone configurations and their effect on driver performance and gaze behavior. The increase in work zone fatalities in the United States between 2015 and 2018 coupled with the limited literature of driver behavior in these complex environments requires a more comprehensive study. Given the nature of these crashes, typically lane departures, gaze behavior provided an additional physiological dimension to the present research. A framework that comprises of the interactions between driver characteristics, mental workload, and situation awareness, with longitudinal control, lateral control, and gaze behavior is proposed. Crash analysis and a simulator study with 90 participants were carried out to investigate the performance and gaze-based changes with respect to various work zone configurations. Distracted driving was also studied by including a secondary task. The results showed a significant interaction between the longitudinal control and the standard deviation of horizontal gaze position in predicting lateral control. Also, significant differences in lateral control and horizontal gaze variations were observed between genders. Female drivers showed lower lateral position deviations and lower horizontal gaze variability. This was a key finding given the inherently higher number of work zone crashes involving male drivers. Placing work zone barriers further away, by up to one meter from pavement edges, could significantly decrease mental workload and improve safety in work zones.

Observer-based backstepping control method using reduced lateral dynamics for autonomous lane-keeping system

This paper presents a backstepping control method with an augmented observer for an autonomous lane-keeping system. A novel reduced second-order model is also derived for an autonomous lane-keeping system. The proposed reduced model of lateral vehicle motion has the following advantages: (1) The lateral motion of the vehicle can be controlled with only simple linear second-order dynamics via the backstepping procedure; (2) The state variable of the reduced model includes the look-ahead distance similar to that for a human driver; (3) The system functions with unknown parameters and external disturbances can be lumped in the disturbance. An augmented observer is designed to estimate the full state and lumped disturbance, including the system functions with unknown parameters and external disturbances. A backstepping control is developed for improving the lateral control and compensation of the disturbance. The stability of the closed-loop system is demonstrated using the input-to-state stable property. The lateral control performance of the proposed method is validated via numerical simulations using CarSim and MATLAB/Simulink.

Cannabis effects on driving lateral control with and without alcohol

BACKGROUND

Effects of cannabis, the most commonly encountered non-alcohol drug in driving under the influence cases, are heavily debated. We aim to determine how blood Δ(9)-tetrahydrocannabinol (THC) concentrations relate to driving impairment, with and without alcohol.

METHODS

Current occasional (≥1×/last 3 months, ≤3days/week) cannabis smokers drank placebo or low-dose alcohol, and inhaled 500mg placebo, low (2.9%)-THC, or high (6.7%)-THC vaporized cannabis over 10min ad libitum in separate sessions (within-subject design, 6 conditions). Participants drove (National Advanced Driving Simulator, University of Iowa) simulated drives (∼0.8h duration). Blood, oral fluid (OF), and breath alcohol samples were collected before (0.17h, 0.42h) and after (1.4h, 2.3h) driving that occurred 0.5-1.3h after inhalation. We evaluated standard deviations of lateral position (lane weave, SDLP) and steering angle, lane departures/min, and maximum lateral acceleration.

RESULTS

In N=18 completers (13 men, ages 21-37years), cannabis and alcohol increased SDLP. Blood THC concentrations of 8.2 and 13.1μg/L during driving increased SDLP similar to 0.05 and 0.08g/210L breath alcohol concentrations, the most common legal alcohol limits. Cannabis-alcohol SDLP effects were additive rather than synergistic, with 5μg/L THC+0.05g/210L alcohol showing similar SDLP to 0.08g/210L alcohol alone. Only alcohol increased lateral acceleration and the less-sensitive lane departures/min parameters. OF effectively documented cannabis exposure, although with greater THC concentration variability than paired blood samples.

CONCLUSIONS

SDLP was a sensitive cannabis-related lateral control impairment measure. During drive blood THC ≥8.2μg/L increased SDLP similar to notably-impairing alcohol concentrations. Despite OF's screening value, OF variability poses challenges in concentration-based effects interpretation.

Dual tasking affects lateral trunk control in healthy younger and older adults

Assessing the effects of attention-demanding tasks on trunk movement provides useful insights into postural control while walking in an attention-split situation, such as occurs in daily life. The coefficient of attenuation of acceleration (CoA) at the trunk is a useful gait index to assess whole trunk movements. We investigated the effect of attention-demanding tasks on CoA to assess the role of attention on trunk control during walking. Thirty healthy, community-dwelling older adults (70.1±5.6 years) and 38 younger adults (22.1±3.4 years) participated in this study. Participants walked 20 m at a self-selected speed (slow, normal, fast) and while performing an attention-demanding cognitive task. Trunk acceleration was measured using triaxial accelerometers attached to the lower (L3 spinous process) and upper (C7 spinous process) trunk and used to compute CoA (the reduction in acceleration from the lower to upper trunk). Results showed that an attention-demanding task significantly decreased CoA in the medio-lateral (ML) direction in both age groups (p<0.001), whereas it did not affect CoA in the vertical (VT) and anterior-posterior (AP) directions. Our findings suggest that the priority of whole trunk control in the ML direction may be higher than in other directions and be strongly associated with attention, whereas whole trunk control in the VT and AP directions may be passively regulated and require minimal attentional control.