We investigated propagation of radio frequency (RF) waves in tunnels. An understanding of RF propagation in tunnels is needed to plan for optimal radio communication system performance. We considered tunnels with a square cross section and right-angle junctions. We developed an analytic model of tunnel propagation by considering multiple reflections from tunnel walls and diffraction around junction corners. A comparison of model results with measurements shows a strong correlation between model predictions and measured data. Finally, we briefly describe a software tool that helps users visualize field strength of the propagating field in tunnels.