1. A method performed by a positioning system of a vehicle for determining a longitudinal position of the vehicle along a road, the road comprising one or more road markings arranged on a surface of the road, the method comprising: detecting, by a sensor, a plurality of road markings; matching, by a matching unit, road markings of the plurality of road markings with mapped road markings of stored map data based on comparing detected characteristics of the plurality of road markings with mapped characteristics of the mapped road markings, wherein the mapped characteristics comprise one or a combination of distances, intervals or relations between road markings; identifying, by an identifying unit, a mapped identified road marking determined to correspond with a detected identified road marking of the plurality of road markings; and determining, by a positioning determining unit, a longitudinal positioning estimate of the vehicle along the road based on a mapped road marking position associated with the mapped identified road marking.