Obstacle Layout Optimization in Crowd Evacuation

Problem Description
Obstacle layout optimization refers to the problem of improving personnel flow efficiency, reducing congestion, and evacuation time in crowd evacuation scenarios by scientifically adjusting the position, shape, and density of obstacles (such as guardrails, green belts, fixed facilities, etc.). Its core lies in using obstacles to guide or restrict the direction of pedestrian flow, avoiding local bottlenecks or path conflicts caused by unreasonable spatial structures. For example, in a large shopping mall fire evacuation, reasonably placing guardrails can prevent blind cross-flows of crowds and enhance overall safety.

Solution Process

1. Problem Modeling: Defining Objectives and Constraints

   • Objective: Minimize total evacuation time (or maximize average flow speed).
   • Key Variables: Position, dimensions, orientation (e.g., whether movable), density of obstacles.
   • Constraints:
     • Safety constraints: Obstacles must not block main exits or fire lanes.
     • Physical constraints: Obstacles must comply with actual spatial dimensions (e.g., width must allow wheelchair passage).
     • Dynamic constraints: Obstacle layout must adapt to changes in crowd density (e.g., differences between peak and off-peak hours).
   • Common Methods: Discretize the space into grids (e.g., cellular automaton models), with obstacles occupying specific grid cells.

2. Analyzing Pedestrian Flow Dynamics

   • Observe natural flow patterns of crowds in unobstructed spaces (e.g., tendency for shortest paths, herd behavior).
   • Identify potential conflict points: For example, areas near exits, channel intersections, and blind spots prone to congestion.
   • Use simulation tools (e.g., FDS+Evac, AnyLogic) to simulate baseline scenarios (unoptimized layout) and record congestion locations and time data.

3. Designing Obstacle Layout Strategies

   • Diversion Strategy: Place diagonal obstacles in wide passages to split a single flow into multiple smaller streams, reducing head-on conflicts (similar to diverge islands on highways).
     • Example: In plaza evacuations, place V-shaped obstacles to guide crowds toward side exits.
   • Buffer Strategy: Set up curved or zigzag obstacles in front of exits to forcibly reduce the approach speed of crowds and avoid "clogging-impact" cycles.
     • Principle: Use physical constraints to cause the crowd to decelerate in advance, reducing pressure accumulation at exits.
   • Guidance Strategy: Use combinations of obstacles to form "soft channels" (e.g., Z-shaped layouts) to indirectly control movement direction and prevent blind acceleration on straight paths.

4. Application of Optimization Algorithms

   • Heuristic Search: Such as genetic algorithms, encoding obstacle layouts as gene sequences and iteratively evolving (selection, crossover, mutation) to screen for optimal solutions.
     • Steps:
       1. Randomly generate multiple layout schemes (initial population).
       2. Calculate evacuation time for each scheme (fitness function).
       3. Retain excellent schemes, combine them to generate new layouts, and introduce random perturbations.
       4. Repeat until convergence (e.g., no improvement for several consecutive generations).
   • Local Search: Fine-tune obstacle positions in key areas and compare simulation results before and after adjustments.

5. Verification and Sensitivity Analysis

   • Use multiple sets of simulations to verify the robustness of the optimized scheme under different crowd densities and behavior patterns (e.g., panic levels).
   • Check extreme scenarios: For example, whether the layout can still maintain effective flow diversion if a certain exit suddenly closes.
   • Supplement verification of simulation results with field tests (e.g., virtual reality drills).

Example Illustration
Assume a stadium evacuation scenario:

• Problem: The main exit leads directly to the parking lot, but crowds rushing toward the exit tend to pile up at the doorway.
• Optimization Solution:
  1. Place curved guardrails 50 meters in front of the exit to naturally split the crowd into left and right streams.
  2. Place planters as obstacles at channel intersections to prevent lateral crowds from crossing the main passage.
• Effect: Simulation shows a 15% reduction in evacuation time and a 30% decrease in peak density at the exit.

Through the above steps, obstacle layout optimization progresses from qualitative strategies to quantitative calculations, ultimately forming implementable safety design plans.