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 (D) 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 overlap the primary coverage (155; 156) of the other camera pair 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 (D) 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 overlap the primary coverage (155; 156) of the other camera pair respectively. <EOS>