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Ethernet has become the de facto standard for providing data transport not only throughout the Internet but also for numerous private and industrial networks. Before Ethernet's dominance, circuit-switched networks (or time-division multiplexed networks such as synchronous optical network (SONET) are popular choices for applications that require flexible and reliable data transport. Over the past ten years, packet-switched networks in general (and Ethernet in particular) usurped the role formerly played by these circuit-switched networks. But is this a good development given that not all applications that require data transport are created equally? This article explores the current trend of using packet-switched as opposed to circuit-switched networks in the context of providing data transport for rail-based public transit agencies and, after examining five case studies, draws conclusions that are relevant for public transit agencies.