Research on Calculation of Warning Zone Length of Freeway Based on Micro-Simulation Model

Ge, Huimin; Yang, Yousen · 2020 · OpenAlex-citations

DOI: 10.1109/access.2020.2989471

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Summary

This study addresses the critical safety and efficiency challenges associated with determining the optimal length of warning zones in freeway maintenance work areas. Traditional methods only provide minimum length requirements, failing to account for the complex trade-off between traffic delay and accident risk. The authors note that warning zones account for 72% of accidents in maintenance areas due to complex driving maneuvers like lane changes and deceleration. To resolve this, the paper proposes a method to calculate the optimal warning zone length using a micro-simulation model (VISSIM) combined with a Surrogate Safety Assessment Model (SSAM). The methodology involves constructing a VISSIM simulation model based on field data from the Hu-Rong freeway in Anhui Province, China. The model simulates a two-way four-lane freeway with an outer lane closure. The simulation parameters, specifically standstill distance (CC0) and desired time headway (CC1), were calibrated against observed traffic capacity to ensure accuracy, resulting in optimized values of 3.5m and 1.1s, respectively. Traffic conflicts were identified using an improved Time to Collision (TTC) model, with a threshold of 2.0s determined via the 85% cumulative frequency method from field-collected trajectory data. The validity of the simulation and threshold was verified using the Mean Absolute Percentage Error (MAPE) and linear regression against observed conflict data. The study then analyzed the relationship between warning zone length (varying from 2000m to 2600m in 100m increments) and safety metrics under varying traffic volumes (1400–2000 pcu/h). The results demonstrate that the simulated traffic conflicts are highly consistent with observed data, with a MAPE of 10.2% and a regression coefficient of determination ($R^2$) of 0.976. Analysis of the simulation outputs reveals that travel time and delay increase slowly as the warning zone length increases. Conversely, the number of traffic conflicts decreases significantly as the warning zone lengthens, showing a convergence state when the length exceeds 2200 meters. A safety evaluation index, defined as the ratio of traffic conflicts to throughput and length, was used to balance safety and efficiency. The study found that at a warning zone length of 2200 meters, the number of traffic conflicts, delay, and the safety evaluation index all reached their minimum values, indicating the highest level of safety and operational efficiency. The significance of this research lies in providing a data-driven, simulation-based approach to optimize freeway maintenance zone design. By identifying 2200 meters as the optimal warning zone length for the studied conditions, the method offers a practical tool for traffic engineers to enhance safety while minimizing unnecessary traffic delays. This approach improves upon traditional static guidelines by dynamically accounting for traffic volume and conflict patterns, contributing to safer and more efficient freeway maintenance operations.

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• emergency work zone conspicuity