Modern-day train operations rely on wireless communications. Unlike other mobile systems, the train vehicle operations are tightly interwound with and remain physically close to the railway and the trackside infrastructure, providing a suitable platform to deploy leaky-waveguide-based communication. Due to the train system's safety-critical application and its exposure to the public, it is critical to address security in train communications. To investigate the availability of leaky waveguide communications, we first study prior leaky waveguide implementations in train systems and, based on those studies, construct a model to characterize the path loss of inside-waveguide propagation and the repeater implementations. Using our model, we analyze the jamming impact and contrast with jamming in free space without a waveguide. As a result, we establish that jamming the waveguide takes advantage of the waveguide infrastructure to extend its impact beyond the traditional jamming range and breaks the spatial dependence on the jamming source.