An apparatus and method are disclosed for calculation of a dangerous road strand of a roadway. Probe data for a roadway having multiple lanes is identified. A subset of the probe data for a predetermined lane is selected and values for a change in velocity for multiple sequences in the subset of probe data are calculated. Based on clustering for the change in velocity and a danger value, the dangerous road strand is identified. The dangerous road strand is stored in a geographic database in association with the lane for the roadway.