1. A method comprising: receiving probe data from radar sensors of vehicles at a road segment, the probe data comprising (1) an identification of static objects and dynamic objects in proximity to the respective vehicles at the road segment and (2) geographic locations of the static objects and the dynamic objects; determining, using a processor, a reference point at the road segment from the identified static objects; calculating lateral distances between the identified dynamic objects and the reference point, the lateral distance measured along an axis perpendicular to lanes of the road segment; and ascertaining a number of lanes at the road segment from a distribution of the calculated distances of the identified dynamic objects from the reference point.