Process modeling grammars are used to create models of business processes. In this paper, the authors discuss how different routing symbol designs affect an individual's ability to comprehend process models. They conduct an experiment with 154 students to ascertain which visual design principles influence process model comprehension. Their findings suggest that design principles related to perceptual discriminability and pop out improve comprehension accuracy. Furthermore, semantic transparency and aesthetic design of symbols lower the perceived difficulty of comprehension. Their results inform important principles about notational design of process modeling grammars and the effective use of process modeling in practice.