Stereoscopic sensor (100, 100_n) comprising: a first camera pair for capturing a first and a second image, said images being processable into a height image; a second camera pair for capturing a first and a second image, said images being processable into a height image, wherein the stereoscopic sensor (100, 100_n) is adapted to monitor and define a main surveillance zone for vehicles traveling in a direction X in a surveillance plane, where the surveillance plane is extending in the direction X and in a direction Y and is acting as a reference plane when combining images captured by the first camera pair and the second camera pair, where the stereoscopic sensor (100, 100_n) with the first camera pair and the second camera pair is located at a predetermined distance in a direction Z above the surveillance plane with a projected mounting position in the surveillance plane being a line extending in the direction Y, wherein the directions X, Y and Z are orthogonal to each other, wherein the first camera pair defines a first surveillance zone with a primary coverage in the surveillance plane in a first direction from the projected mounting position and a secondary coverage in a second direction from the projected mounting position, wherein the first and second directions (161. 162) are oppositely directed from the projected mounting position in the direction X, wherein the second camera pair defines a second surveillance zone with a primary coverage in the surveillance plane in the second direction from the projected mounting position and a secondary coverage in the first direction from the projected mounting position, wherein said secondary coverage (157; 158) of the first and the second camera pairs (110, 120) overlap the primary coverage (155; 156) of the other camera pair (110, 120) respectively. a first camera pair for capturing a first and a second image, said images being processable into a height image; a second camera pair for capturing a first and a second image, said images being processable into a height image, wherein the stereoscopic sensor (100, 100_n) is adapted to monitor and define a main surveillance zone for vehicles traveling in a direction X in a surveillance plane, where the surveillance plane is extending in the direction X and in a direction Y and is acting as a reference plane when combining images captured by the first camera pair and the second camera pair, where the stereoscopic sensor (100, 100_n) with the first camera pair and the second camera pair is located at a predetermined distance in a direction Z above the surveillance plane with a projected mounting position in the surveillance plane being a line extending in the direction Y, wherein the directions X, Y and Z are orthogonal to each other, wherein the first camera pair defines a first surveillance zone with a primary coverage in the surveillance plane in a first direction from the projected mounting position and a secondary coverage in a second direction from the projected mounting position, wherein the first and second directions (161. 162) are oppositely directed from the projected mounting position in the direction X, wherein the second camera pair defines a second surveillance zone with a primary coverage in the surveillance plane in the second direction from the projected mounting position and a secondary coverage in the first direction from the projected mounting position, wherein said secondary coverage (157; 158) of the first and the second camera pairs (110, 120) overlap the primary coverage (155; 156) of the other camera pair (110, 120) respectively.