Mechanism Design for Locating a Bridge Between Regions with Prelocated Facilities

2026-07-05

AI Summary

This study addresses the mechanism design problem of locating a bridge between two predefined facility regions when agents’ locations are private information, with the objective of minimizing either the maximum individual cost or the total social cost. Focusing on a cost model where agents traverse the bridge to reach their nearest facility, this work presents the first systematic analysis of this cross-regional facility location setting and introduces both deterministic and randomized approximation mechanisms satisfying group strategyproofness (GSP) and strong group strategyproofness (SGSP). The main contributions include: for the maximum cost objective, an optimal GSP mechanism, a 3-approximate deterministic SGSP mechanism, and a 2-approximate randomized SGSP mechanism; for the social cost objective, a 3-approximate deterministic GSP mechanism and a 2-approximate randomized GSP mechanism, along with established lower bounds on approximation ratios across several settings.

Abstract

In many urban planning projects, social planners require the construction of a bridge to connect two regions separated by obstacles such as rivers or highways. This paper studies the mechanism design problem for locating a bridge between two separate regions, each of which has been equipped with a facility. There are a set of agents located in each region and each agent has her location as private information. Once the bridge is built, the agents will go to the nearest facility to receive service and each agent's cost is the distance from her location to the nearest prelocated facility via the bridge. We investigate social cost and maximum cost under strategyproof (SP) mechanisms, with stronger notions of group-strategyproof (GSP) and strong group-strategyproof (SGSP). For the maximum cost objective, we characterize the optimal solution and show that it satisfies GSP. Under the SGSP, we propose a deterministic 3-approximation mechanism and a randomized 2-approximation mechanism, while proving a lower bound of 2 for any deterministic SGSP mechanism. For the social cost objective, we present a deterministic 3-approximation mechanism and a randomized 2-approximation mechanism that satisfy GSP. We establish lower bounds of 2 and 1.1 for deterministic and randomized SP mechanisms, respectively. Under the SGSP, the lower bound for deterministic mechanisms increases to 1 + min{m, n}, and we provide a (1 + 2 min{m, n})-approximation mechanism. For randomized mechanisms, the lower bound remains 1.1, while an upper bound of (1 + 2mn/(m+n)) is achieved.

Problem

• Mechanism Design
• Bridge Location
• Strategyproofness
• Social Cost
• Maximum Cost

Innovation

• Mechanism Design
• Strategyproofness
• Bridge Location
• Approximation Mechanism
• Facility Location