Informal and privatized transit services, such as minibuses and shared auto-rickshaws, are integral to daily travel in large urban metropolises, providing affordable commutes where a formal public transport system is inadequate and other options are unaffordable. Despite the crucial role that these services play in meeting mobility needs, governments often do not account for these services or their underlying incentives when planning transit systems, which can significantly compromise system efficiency. Against this backdrop, we develop a framework to analyze the incentives underlying informal and privatized transit systems, while proposing mechanisms to guide public transit operation and incentive design when a substantial share of mobility is provided by such profit-driven private operators. We introduce a novel, analytically tractable game-theoretic model of a fully privatized informal transit system with a fixed menu of routes, in which profit-maximizing informal operators (drivers) decide where to provide service and cost-minimizing commuters (riders) decide whether to use these services. Within this framework, we establish tight price of anarchy bounds which demonstrate that decentralized, profit-maximizing driver behavior can lead to bounded yet substantial losses in cumulative driver profit and rider demand served. We further show that these performance losses can be mitigated through targeted interventions, including Stackelberg routing mechanisms in which a modest share of drivers are centrally controlled, reflecting environments where informal operators coexist with public transit, and cross-subsidization schemes that use route-specific tolls or subsidies to incentivize drivers to operate on particular routes. Finally, we reinforce these findings through numerical experiments based on a real-world informal transit system in Nalasopara, India.

翻译：非正式及私营化交通服务（如小型巴士与共享电动三轮车）已成为大型都市日常出行的重要组成部分，在为正规公共交通系统不足且其他出行方式难以负担的地区提供经济通勤方案。尽管这些服务在满足出行需求方面发挥着关键作用，政府在规划交通系统时却往往忽视这些服务及其内在激励，从而可能严重损害系统效率。在此背景下，我们构建了一个分析框架，用以剖析非正式及私营化交通系统的内在激励机制，同时提出在营利性私营运营商承担主要出行服务份额时指导公共交通运营与激励设计的机制。我们引入了一种新颖且可解析的博弈论模型，描述具有固定线路菜单的完全私营化非正式交通系统，其中利润最大化的非正式运营商（驾驶员）决定服务供给区域，而成本最小化的通勤者（乘客）决定是否使用这些服务。在此框架内，我们建立了严格的"无政府状态代价"界限，证明去中心化的利润最大化驾驶员行为可能导致驾驶员累计利润与服务乘客需求产生有限但显著的损失。我们进一步表明，通过针对性干预措施可缓解这些性能损失，包括：采用斯塔克尔伯格路由机制（使少量驾驶员受中央调控，反映非正式运营商与公共交通共存的场景），以及实施跨线路补贴方案（通过特定线路收费或补贴激励驾驶员运营特定路线）。最后，我们基于印度纳拉索帕拉地区的真实非正式交通系统进行数值实验，进一步验证了这些发现。