Coalitions in nonatomic network congestion games

TL;DR

This paper demonstrates that forming a limited number of coalitions in nonatomic network congestion games reduces costs for all participants, with equilibrium outcomes favoring smaller coalitions and individual players.

Contribution

It introduces a model analyzing the effects of coalition formation in nonatomic congestion games and characterizes equilibrium properties and convergence behavior.

Findings

Coalitions lower costs for everyone involved.

Individuals benefit when some members form coalitions.

Equilibria converge as coalition sizes diminish.

Abstract

This work shows that the formation of a finite number of coalitions in a nonatomic network congestion game benefits everyone. At the equilibrium of the composite game played by coalitions and individuals, the average cost to each coalition and the individuals' common cost are all lower than in the corresponding nonatomic game (without coalitions). The individuals' cost is lower than the average cost to any coalition. Similarly, the average cost to a coalition is lower than that to any larger coalition. Whenever some members of a coalition become individuals, the individuals' payoff is increased. In the case of a unique coalition, both the average cost to the coalition and the individuals' cost are decreasing with respect to the size of the coalition. In a sequence of composite games, if a finite number of coalitions are fixed, while the size of the remaining coalitions goes to zero, the equilibria of these games converge to the equilibrium of a composite game played by the same fixed coalitions and the remaining individuals.