1. A method comprising: receiving probe data from radar sensors of vehicles at a road segment, the probe data comprising an identification of static objects and dynamic objects in proximity to the respective vehicles at the road segment, and geographic locations of the static objects and the dynamic objects; determining, using a processor, a common reference point at the road segment among the identified static objects received from the vehicles; calculating lateral distances between the identified dynamic objects and the common reference point using the geographic locations of the identified dynamic objects and the common reference point, each lateral distance measured along an axis laterally perpendicular to lanes of the road segment; ascertaining a number of lanes at the road segment from a distribution of the calculated distances of the identified dynamic objects from the common reference point, wherein the distribution of the calculated distances of the identified dynamic objects is arranged in a histogram, and the number of lanes at the road segment are ascertained based on a number of peaks in the histogram; and updating a map database with the ascertained number of lanes at the road segment.