A device for distinguishing between traversable and non-traversable objects. The device includes: an object-detection sensor unit configured generate data about a space around the sensor, a map generation unit configured to use the data to generate an occupancy grid map and a free space grid map for the space around the object-detection sensor unit. Each of the occupancy grid map and the free space grid map includes an array of cells. Each cell of the occupancy grid map contains an occupied space probability value representing the probability for the respective cell being occupied and each cell of the free grid map contains a free space probability value representing the probability for the respective cell being free. The device includes a classifier unit configured to classify at least one of the cells as containing a traversable or non-traversable object by calculating a difference of two free space probability values derived from the free space probability values of at least two of the cells adjacent to the at least one cell and by using the difference as well as the occupied space probability value of the at least one cell to classify the at least one cell.