1. A probabilistic lane assignment method for an object in a scene forward of a host, where the host is traveling in one lane of a multiple lane road, the method comprising the steps of: determining an off-center distance of the host from a center of said one lane, and estimating a mean of said off-center distance and a variance that reflects uncertainty in the determination of said off-center distance; sensing downrange and lateral coordinates of the object relative to a host coordinate system, and estimating a mean of said lateral coordinate and a variance that reflects uncertainty in the sensing of said lateral coordinate; determining an apparent curvature of the host ego lane, and estimating a mean of said curvature and a variance that reflects uncertainty in the determination of said curvature; determining a lateral coordinate of the host's ego lane center at the obtained downrange coordinate of the object, and estimating a mean of said lateral coordinate of the host's ego lane center and a variance based on at least the estimated mean and variance of said apparent curvature; determining a width of said one lane, and estimating a mean of said width and a variance that reflects uncertainty in the determination of said width; combining the mean and variance of at least the lateral coordinate of the object, with the mean and variance of the determined lateral coordinate of the host's ego lane center at the downrange coordinate of the object, and with the mean and variance of the determined lane width to form a lane assignment for the object, said lane assignment including a lane designation and an indication of confidence or degree-of-belief in the lane designation; determining a variance of said lane assignment by combining the mean and variance of the lateral coordinate of the object, with the mean and variance of the lateral coordinate of the host's ego lane center at the obtained downrange coordinate of the object, with the mean and variance of the off-center distance, and with the mean and variance of the determined width of said one lane; and utilizing the calculated lane assignment to assess a threat the object poses to the host.