Variable Speed Limit Method for Rainy Weather Considering Freeway Operation Risk

To ensure the safe driving of freeway traffic in rainy environments and reduce operation risk, a variable speed limit (VSL) management mode can be adopted to control the operation risks of freeways in rainy weather. First, the random forest analysis model was used to calibrate the feature importance of dynamic and static risk factors, and the entropy value theory was used to establish a risk analysis model of a freeway. Combining the model with the risk characteristics of dynamic traffic operations in rainy weather, the dynamic operation risk coefficient of expressways was calculated, and the risk level was determined. Subsequently, based on the variation law of VSL in Mainstream Traffic Flow Control and the characteristics of large and small vehicles, stopping sight-distance, water film thickness, expected risk, and other factors, the VSL model of freeways in rainy weather was optimized. The initial VSL control values for the large and small vehicles were refined. Then, a VSL for rainy days was proposed. Finally, a driving simulation system, a psychophysics-physiological testing equipment, and traffic flow simulation software VISSIM were used to verify the rationality of the control value based on the driver's driving adaptability and traffic flow. The results show that as visibility decreases and rainfall increases, under the VSL management of this study, the drivers' sympathetic nerve excitability weakened, whereas their parasympathetic nerve excitability enhanced, and their psychological tension reduced. The mean heart rate, high-frequency value, low-frequency value, and difference in heart rate variability of the drivers change from 74.13, 0.121, 0.643, and 2.37 to 78.23, 0.192, 0.567, and 2.01, respectively. These results indicate that drivers demonstrate good adaptability to the proposed speed. In addition, the verification results of the traffic flow operation state show that the VSL can ensure the overall traffic efficiency of the road and does not cause traffic flow risk vibrations. When the speed limit of small and large vehicles is 80 and 60 km·h-1, or the speed limit of the small is 60 km·h-1 and the driving of the large is forbidden, the mean and median time-to-collision values exceed those in a scenario without a speed limit, which shows that the safety performance of each lane can be guaranteed. In conclusion, the VSL control method proposed herein exhibits certain rationality and engineering adaptability, and can provide theoretical support for the active prevention and control of macro traffic flow on freeways in severe weather. © 2022 Xi'an Highway University. All rights reserved.