Traffic information is required to perform optical-layer traffic engineering (TE). However, as the number of nodes in optical networks increases, the overhead for collecting the traffic volume information becomes large. In this paper, we develop a method that reduces the overhead for collecting traffic volume information by selecting a subset of nodes and by only collecting the traffic volume information from the selected nodes. Then, we estimate the traffic volume using the information gathered from the selected nodes. According to the simulation results, we clarify that our method can accurately identify the congested links in real ISP topologies, where the number of traffic demands passing through some links is large; however, the estimation errors of our method become large when the number of traffic demands passing each link is small. Furthermore, optical-layer TE can sufficiently mitigate congestion by using the traffic volume estimated by our method from the information on 50% of all nodes in the case of the Japan topology and 30% of all nodes in the case of the AT&T topology.