1. A road curvature estimation system, comprising: a. a plurality of road curvature estimation subsystems selected from a first road curvature estimation subsystem adapted to estimate a first set of at least one first curvature parameter responsive to a measure of longitudinal speed of a host vehicle on a roadway and a measure of yaw rate of said host vehicle, a second road curvature estimation subsystem adapted to estimate a second set of at least one second curvature parameter responsive to a measure of said second set of at least one second curvature parameter from a map database responsive to a measure of location of said host vehicle, and a third road curvature estimation subsystem adapted to estimate a third set of at least one third curvature parameter responsive to a radar measurement of a target vehicle traveling on said roadway; and b. a processor adapted to fuse at least two of said first set of at least one first curvature parameter, said second set of at least one second curvature parameter, and said third set of at least one third curvature parameter so as to generate a fourth set of at least one fourth curvature parameter as an estimate of curvature of said roadway.