Abstract: We present a novel spatio-temporal index for constraint networks,which is called NBR-tree(network-based R-tree).We focus on the background of the applications in urban traffic networks.The NBR-tree is an improvement on the previous index named MON-tree,with an analysis on the specific properties of the moving objects in urban traffic networks.We discuss the index structure,operating algorithms as well as the experiments of the NBR-tree in detail.The experimental results show that our proposed index is able to support NN queries,and is more efficient than the MON-tree in evaluating trajectory queries.