Abstract: In a target track generation apparatus, a subject vehicle reference preceding vehicle position calculator calculates a point group of subject vehicle reference preceding vehicle positions representing a history of a relative position of a preceding vehicle in a coordinate system using a current position of a subject vehicle as a reference. A target track generator generates a target track of the subject vehicle, based on the point group of the subject vehicle reference preceding vehicle positions. A correction target track generator generates a correction target track obtained by correcting the target track, based on the point group of the subject vehicle reference preceding vehicle positions or the target track, when it is determined that correction of the target track is necessary.

Abstract: A propanol sol of silica having a specific surface area of 25 to 550 m.sup.2 /g, the sol having an SiO.sub.2 concentration of 10 to 50% by weight of SiO.sub.2 and a residual content of a medium containing 7.5% by weight or less of water based on the SiO.sub.2 content and 90% by weight or more of propanol, is prepared by an improved process involving replacing the aqueous medium in an acidic aqueous sol of silica containing 5 to 50% by weight of SiO.sub.2 and a medium having a water content of 15% by weight or more with propanol by an atmospheric distillation method in which a concentration of 5 to 50% by weight of SiO.sub.2 in the sol and 1 to 85% by weight of methanol in the medium in the sol is maintained when the medium in the sol during the replacement contains 15 to 0.5% by weight of water.