导航服务的集体影响尚不明确：尽管通常对个体驾驶员有益，但其可能无意中重塑城市交通模式。我们在意大利佛罗伦萨、米兰和罗马开展模拟研究，整合了GPS数据、道路网络及主流导航服务提供商的路径推荐信息。我们识别出一种集聚效应：随着采用率上升，路径多样性下降，交通流与排放逐渐集中于更少的道路。在完全采用情形下，路径多样性较忽略所有路径推荐的基线情形最多降低14%。此外，导航服务在低采用率水平下可减少CO₂排放，但此类效益随采用率升高而减弱、消失，甚至在特定城市与特定服务的阈值之上发生逆转。我们在抽象化实验环境中复现了上述实验，所得结果与真实城市观测结果一致。

The collective impact of navigation services remains unclear: while often beneficial to individual drivers, they can unintentionally reshape urban traffic patterns. We simulate their impact in Florence, Milan, and Rome (Italy), integrating GPS data, road networks, and route recommendations from leading providers. We identify a concentration effect: as adoption increases, route diversity declines, and traffic and emissions converge onto fewer roads. At full adoption, route diversity decreases by up to 14% compared to a baseline where recommendations are ignored. Moreover, navigation services reduce CO2 emissions at low adoption levels, but these benefits diminish, disappear, or even reverse beyond a city- and service-specific threshold. We replicate our experiments in an abstract setting, obtaining results consistent with those observed in real-world cities.