A support system for supporting a coupling operation between a first train unit (Car 1) and a second train unit, each train unit having a respective coupler for coupling to the coupler of the other train unit, and a respective coupler cover which is movable between a closed configuration in which the cover covers its coupler and an open configuration in which the coupler is revealed to allow coupling, the support system including: a distance measuring device mountable at a front of the first train unit and operable to measure a distance between the first train unit and the second train unit; a coupler cover monitoring device mountable to the first train unit (Car 1) and operable to detect an open or closed configuration status of the first train unit's coupler cover; and a protection sub-system mountable to the first train unit (Car 1), the protection sub-system being configured to receive a distance measurement from the distance measuring device and a configuration status from the coupler cover monitoring device, and issue a coupling stop signal when the distance measurement is less than a predetermined threshold distance and the configuration status indicates the first train unit's coupler cover is closed; characterised in that the distance measuring device comprises a camera which is configured to obtain an image of the front of the second train unit, and an image processing unit which is configured to determine the distance between the first train unit and the second train unit from the obtained image, and to determine the open or closed configuration status of the coupler cover of the second train unit from the obtained image, the protection sub-system being also configured to issue the coupling stop signal when the distance measurement is less than a predetermined threshold distance and the image processing unit determines the second train unit's coupler cover is closed. a distance measuring device mountable at a front of the first train unit and operable to measure a distance between the first train unit and the second train unit; a coupler cover monitoring device mountable to the first train unit (Car 1) and operable to detect an open or closed configuration status of the first train unit's coupler cover; and a protection sub-system mountable to the first train unit (Car 1), the protection sub-system being configured to receive a distance measurement from the distance measuring device and a configuration status from the coupler cover monitoring device, and issue a coupling stop signal when the distance measurement is less than a predetermined threshold distance and the configuration status indicates the first train unit's coupler cover is closed; characterised in that the distance measuring device comprises a camera which is configured to obtain an image of the front of the second train unit, and an image processing unit which is configured to determine the distance between the first train unit and the second train unit from the obtained image, and to determine the open or closed configuration status of the coupler cover of the second train unit from the obtained image, the protection sub-system being also configured to issue the coupling stop signal when the distance measurement is less than a predetermined threshold distance and the image processing unit determines the second train unit's coupler cover is closed.