1. A road curvature estimation system, comprising: a. a speed sensor adapted to measure a longitudinal speed of a vehicle on a roadway and to generate a measure of longitudinal speed responsive thereto; b. a source of a measure of yaw rate of said vehicle; and c. a processor operatively coupled to said speed sensor and to said source of said measure of yaw rate, wherein said processor comprises a plurality of curvature estimators associated with a corresponding plurality of different roadway models, each said curvature estimator is adapted to estimate at least one associated curvature parameter of a corresponding said different roadway model, said processor provides for selecting a most likely of said different roadway models as a most likely roadway model, and said processor provides for outputting said at least one curvature parameter of said most likely roadway model as an estimate of curvature of said roadway.