Several wireless communication systems are developed for communication needs between train and ground or between trains in the railway or mass transit domains. In order to deploy these systems in specific environments, such as tunnels, straight or curved, rectangular or arch-shaped section, specific propagation models have to be developed. In this paper, we propose a method to model the radiowave propagation in straight arch-shaped tunnels by using asymptotic methods, such as ray tracing and ray launching, combined with the tessellation of the arched section. A method of interpolation of the facets normals is implemented in order to minimize the error made when using the tessellation. These results are compared to those found in the literature in order to validate our approach.