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This paper presents an evaluation of the traffic characteristics of the overflow routing, which is one of the isolated routings (i.e., only the information in the switching station is utilized) of the packet‐switching network. In the overflow routing, the packet selects the first route if the number of waiting packets in the first route is less than the threshold value, and selects the second route if it is equal to or larger than the threshold. Which of the routes is defined as the first route is determined for each destination of the packet, and the packet deroutes others among the routes. In the first part of this paper, the relation between the transmission‐waiting time in the switching station and the threshold of the overflow routing is derived. Then the two‐level hierarchical packet‐switching network is considered, and the mutual overflow routing, SQ + B routing and the stochastic routing, which is easy to realize with simple processing, are compared from the viewpoint of the transmission delay between the transmitting and receiving stations; SQ + B routing has the best performance in the isolated routings, and the stochastic routing features in the simple processing and the easy representation. As a result, it is shown that the transmission delay in the mutual overflow routing is less than in the stochastic routing and is nearly the same as that of SQ + B routing. Since the processing per packet in the mutual overflow routing is less than that of the SQ + B routing, the mutual overflow routing can be considered as the best among the three routing methods.