Enhancing emergency capacity: A gradual cooperative accessibility method considering time-varying traffic congestion and population distribution

Enhancing urban emergency capacity requires a comprehensive evaluation of preparedness to identify vulnerable areas and propose mitigation strategies. Traditional studies on emergency accessibility often rely on the assumption that proximity to the nearest emergency facility is the sole determinant and evaluate accessibility within a fixed time frame. This study introduces a novel gradual cooperative emergency accessibility method that accounts for time-varying traffic congestion and population distribution. The gradual accessibility component, using a delay function, defines the single accessibility provided by an emergency facility to a demand point, while the cooperative accessibility component considers the combined accessibility from multiple facilities to a demand point. Recognizing that traffic congestion affects emergency vehicle travel times, we discretize time-varying travel speeds into piecewise functions, ensuring that link travel times adhere to the network's first-in–first-out property. This approach allows us to modify existing shortest-path algorithms to efficiently solve time-dependent shortest-path problems. Additionally, this method accounts for the interactions and cooperation among various emergency services. To validate its applicability, this method is applied to assess urban emergency accessibility during the construction of the Pinglu Canal. The results reveal a distribution of emergency accessibility within the study area, highlighting significant weaknesses in the northern region and comparatively lower levels in the southern region. Corresponding improvement measures are proposed to enhance emergency accessibility in these vulnerable areas. Furthermore, two sensitivity analyses demonstrate that considering time-varying traffic congestion and population distribution yields more accurate and human-centered results.