1. A method for regulating a vehicle's speed comprising: A) determining a horizon from position data and map data of an itinerary made up of route segments with length and gradient characteristics for each segment; B) calculating threshold values for the gradient of segments according to one or more vehicle-specific values, wherein the threshold values serve as boundaries for assigning segments to various categories; C) comparing the gradient of each segment with the threshold values and placing each segment within the horizon in a category according to the results of the comparisons; for each segment within the horizon which is in a category indicating a steep upgrade or a steep downgrade, the method comprises: D) calculating the vehicle's final speed v end after the end of the segment, based inter alia on the entry speed v i to the segment; and if the calculated final speed v end is outside the range for the vehicle's current reference speed v set defined by v max and v min , the method performs the step of E) correcting the entry speed v i for the segment on the basis of the calculated final speed v end for the segment, wherein the correction is defined by rules for the segment's category, so that v min ≦v end ≦v max , on the supposition that v i is corrected within the same range; F) regulating the vehicle's speed according to speed set-point values v ref based on the entry speeds v i to each segment.