as previously mentioned in certain types of accident such as for example a roll over situation when the vehicle rotates around its longitudinal axis there is a risk that the head 3 of the driver 2 will be pushed against the inside of the roof 4 with great force in a serious accident this can cause damage to the driver 39 s head and neck if the head 3 of the driver 2 hits the roof 4 with great force one of the fundamental principles behind the present invention is that the inside of the roof 4 includes a structure 5 that is specially designed to guide the head 3 of the driver 2 under the abovementioned accident conditions in such a way that a flexion of the neck 6 of the driver 2 is initiated at the same time as his or her head 3 hits the inside of the inside of roof 4 for this purpose the device is designed in a first embodiment so that the inside of the roof is equipped with a structure 5 consisting of a first layer of material which is nearest the head 3 of the driver 2 and which is made of a relatively hard and rigid material a second layer of material.