Extendable ramp and sensor arrangement

An extendible ramp 1 for entrance to or egress from vehicles, such as buses includes sensors (15, Figure 6) arranged to detect whether the ramp abuts an obstruction. The ramp assembly comprises a chassis 4, a ramp 1 extendible from the chassis 4, a frame 11 which carries the chassis 4 and a sensor (15) arranged to sense movement of the chassis 4 relative to the frame 11. The chassis 4 may be mounted in the frame 11 such that it moves relative to the frame 11 in response to both abutment of the leading edge of the ramp 1 against an obstacle and in response to vertical force applied to the top of the extended or partially extended ramp 1. The chassis 4 optionally also moves relative to the frame 11 in response to a force applied to the side of the extended or partially extended ramp 1. Preferably the chassis 4 is pivotally suspended from the frame 11 by at least two pivoting links which are inclined relative to each other.