A system for preventing semitrailer collisions with a loading ramp comprising: - a sensor unit comprising a sensor and configured for sensing when the rear end of a semitrailer is approaching a loading ramp; - a guide block adapted to be positioned on the ground, laterally and/or medially to the opening of a loading ramp; wherein the guide block comprises a first wheel blocking means configured as a sled adapted for supporting the tread of a rear tire of said semitrailer, and configured to move, preferably passively, from a forwarded position relative to said loading ramp to a retracted position relative to said loading ramp when being pushed by said rear tire as said semitrailer is reversing towards said loading ramp; wherein said sensor unit is configured to send a blocking signal to said guide block when the distance between said rear end of said semitrailer and said loading ramp is below a preset threshold, wherein said wheel blocking means locks its position in response to said blocking signal, thereby blocking the movement of said sled; wherein the system further comprises: - a rain flap isolation device adapted for preventing said rear tire and its rain flap from touching each other while said rear tire is positioned within said sled during its movement from a forwarded position relative to said loading ramp to a retracted position relative to said loading ramp when being pushed by said rear tire as said semitrailer is reversing towards said loading ramp; and said system being characterized in that said rain flap isolation device comprises: i) a first part integrated into or connected to the sled and comprising a plate or rod adapted for moving between a retracted position and an extended position; and ii) an activation means configured for activating the plate or rod to move from the retracted position to the extended position; wherein the plate or rod moves upwards relative to the sled when in the extended position. - a sensor unit comprising a sensor and configured for sensing when the rear end of a semitrailer is approaching a loading ramp; - a guide block adapted to be positioned on the ground, laterally and/or medially to the opening of a loading ramp; wherein the guide block comprises a first wheel blocking means configured as a sled adapted for supporting the tread of a rear tire of said semitrailer, and configured to move, preferably passively, from a forwarded position relative to said loading ramp to a retracted position relative to said loading ramp when being pushed by said rear tire as said semitrailer is reversing towards said loading ramp; wherein said sensor unit is configured to send a blocking signal to said guide block when the distance between said rear end of said semitrailer and said loading ramp is below a preset threshold, wherein said wheel blocking means locks its position in response to said blocking signal, thereby blocking the movement of said sled; wherein the system further comprises: - a rain flap isolation device adapted for preventing said rear tire and its rain flap from touching each other while said rear tire is positioned within said sled during its movement from a forwarded position relative to said loading ramp to a retracted position relative to said loading ramp when being pushed by said rear tire as said semitrailer is reversing towards said loading ramp; and said system being characterized in that said rain flap isolation device comprises: i) a first part integrated into or connected to the sled and comprising a plate or rod adapted for moving between a retracted position and an extended position; and ii) an activation means configured for activating the plate or rod to move from the retracted position to the extended position; wherein the plate or rod moves upwards relative to the sled when in the extended position. i) a first part integrated into or connected to the sled and comprising a plate or rod adapted for moving between a retracted position and an extended position; and ii) an activation means configured for activating the plate or rod to move from the retracted position to the extended position; wherein the plate or rod moves upwards relative to the sled when in the extended position.