A model for printed circuit boards which can be used to predict the probability that a router will successfully make a connection is presented. The model reflects certain characteristics of the circuit board that is being routed and the model incrementally changes as the board is routed. Routing procedures typically have certain parameters which influence selection of the set of paths that are explored, and determine the order of exploration. These parameters obviously influence the probability that a particular connection can be made. These parameters may also be used to formulate a model of the behavior of a particular routing procedure.