Method for detecting passages by vehicles at a virtual gantry controlled by a Global Navigation Satellite System, the GNSS comprising an On Board Unit in every vehicle to be surveyed by the system, a central back office and/ or a proxy, said OBU receiving signals from satellites to consistently and frequently estimate positions for the vehicles, the method being performed by said GNSS system and comprising the steps of: i. defining a virtual gantry in terms of a number of ordered passage lines across a road, each passage line being further defined by a centre point (c), a local road width (w) calculated as the sum of the longitudinal extension (w left) of the passage line to a first or left lateral side of the centre point (c) and the longitudinal extension (w right) of the passage line to the other or right lateral side of the centre point (c) and at each side of the road, a local tolerance (t) defined as a linear extension beyond the local road width (w), ii. for each vehicle for which two in succession estimated positions (p k-1, p k) are localized at different sides of a passage line, determining an intersection point (i) as the point where a straight line between the two positions intersects the passage line in question, iii. calculating a numerical value representing a positive contributory probability value (cpv) for the intersection point at that passage line, by calculating the signed distance d i from centre point (c i) to intersection point (i i) and applying a function thereof also contemplating the local road width (w) and the local tolerances (t), said function assigning a maximum value to the cpv when the intersection point (i i) is in proximity to the centre point, and a minimum value when the intersection point (i i) is at the outer end of a local tolerance (t), iv. for each vehicle for which intersection points (i) according to item ii have been determined for at least two different passage lines (PL i, PL ii,...) within a defined period of time, in the order defined by item i, calculating a total probability value based on the individually calculated, contributory probability values (cpv) calculated as indicated by item iii at each of the at least two passage lines (PL i, PL ii), v. concluding of a true passage by the vehicle in question only if the TPV exceeds a predefined minimum value. i. defining a virtual gantry in terms of a number of ordered passage lines across a road, each passage line being further defined by a centre point (c), a local road width (w) calculated as the sum of the longitudinal extension (w left) of the passage line to a first or left lateral side of the centre point (c) and the longitudinal extension (w right) of the passage line to the other or right lateral side of the centre point (c) and at each side of the road, a local tolerance (t) defined as a linear extension beyond the local road width (w), ii. for each vehicle for which two in succession estimated positions (p k-1, p k) are localized at different sides of a passage line, determining an intersection point (i) as the point where a straight line between the two positions intersects the passage line in question, iii. calculating a numerical value representing a positive contributory probability value (cpv) for the intersection point at that passage line, by calculating the signed distance d i from centre point (c i) to intersection point (i i) and applying a function thereof also contemplating the local road width (w) and the local tolerances (t), said function assigning a maximum value to the cpv when the intersection point (i i) is in proximity to the centre point, and a minimum value when the intersection point (i i) is at the outer end of a local tolerance (t), iv. for each vehicle for which intersection points (i) according to item ii have been determined for at least two different passage lines (PL i, PL ii,...) within a defined period of time, in the order defined by item i, calculating a total probability value based on the individually calculated, contributory probability values (cpv) calculated as indicated by item iii at each of the at least two passage lines (PL i, PL ii), v. concluding of a true passage by the vehicle in question only if the TPV exceeds a predefined minimum value.