Self-interested routing polices from individual users in a system can collectively lead to poor aggregate congestion in routing networks. The introduction of altruistic agents, whose goal is to benefit other agents in the system, can seemingly improve aggregate congestion. However, it is known in that in some network routing problems, altruistic agents can actually worsen congestion compared to that which would arise in the presence of a homogeneously selfish population. This paper provides a thorough investigation into the necessary conditions for altruists to be guaranteed to improve total congestion. In particular, we study the class of series-parallel non-atomic congestion games, where one sub-population is altruistic and the other is selfish. We find that a game is guaranteed to have improved congestion in the presence of altruistic agents (even if only a small part of the total population) compared to the homogeneously selfish version of the game, provided the network is symmetric, where all agents are given access to all paths in the network, and the series-parallel network for the game does not have sub-networks which emulate Braess's paradox -- a phenomenon we refer to as a Braess-resistant network. Our results appear to be the most complete characterization of when behavior that is designed to improve total congestion (which we refer to as altruism) is actually guaranteed to do so.

翻译：系统中个体用户的自私路由策略可能共同导致整个路由网络的总体拥塞恶化。引入以造福系统中其他代理为目标的利他代理似乎能改善总体拥塞。然而，已知在某些网络路由问题中，利他代理实际上可能比同质化自私群体环境下产生的拥塞更严重。本文深入研究了确保利他者能够改善总拥塞的必要条件。具体而言，我们研究了一类串并联非原子拥塞博弈，其中一部分群体为利他者，另一部分为自私者。我们发现，当网络对称（所有代理均可访问网络中的所有路径）且博弈的串并联网络不存在模拟布拉伊斯悖论的子网络时（我们将此类网络称为抗布拉伊斯网络），博弈在有少量利他代理存在的情况下（即使仅占总人口很小比例），其拥塞状况必然优于同质化自私版本。我们的研究结果似乎是对所谓"旨在改善总拥塞的行为（即利他行为）能否真正达成目标"这一命题最完整的特征刻画。