An access device configured to be installed onto a vehicle, adapted to provide access between a substrate surface and an elevated surface of the vehicle, the access device including: a mounting, for securement of said device substantially atop said elevated surface; a first ladder member, a first end of which is pivotally attached to said mounting at a first pivotal connection; a second ladder member, a first end of which is pivotally attached to a second end of said first ladder member, at an articulation joint; drive means, operatively connected between said mounting and said first ladder member, to control movement of said first ladder member between an access position and a storage position; at least one guide arm, operatively connected between said mounting and said articulation joint, to guide movement of said second ladder member as said drive means moves said first ladder member; whereby, said drive means is configured to be operated by a user to control the operation of said access device between the access position and the storage position, in which, in said access position, each of said first and second ladder members (5,6) are substantially coaligned and extend substantially outwardly and downwardly from said elevated surface, and, in said storage position, each of said first and second ladder members (5,6) are retracted in a substantially vertically disposed manner substantially atop said mounting pivoted relative to each other from the access position; characterized in that said drive means includes: a rotatable member having first, second, and third pivotal connectors (21, 22, 23) spaced apart in a triangular arrangement; the first connector being pivotally attached to said mounting; the second connector being pivotally attached to said first ladder member via a control arm at a second pivotal connection; and the third connector being pivotally attached to an upper extremity of said mounting via an extendible arm; whereby, said extendable arm is configured to be contracted or extended to cause said rotatable member to rotate about said first connector, and to consequently effect movement of said access device between said access and storage positions, wherein, in the access position: the third connector is disposed outwardly of the first and second connectors (21, 22), the first connector is disposed inwardly of the second and third connectors (22, 23), and the second connector is disposed upwardly of the first and second connectors (21, 23). a mounting, for securement of said device substantially atop said elevated surface; a first ladder member, a first end of which is pivotally attached to said mounting at a first pivotal connection; a second ladder member, a first end of which is pivotally attached to a second end of said first ladder member, at an articulation joint; drive means, operatively connected between said mounting and said first ladder member, to control movement of said first ladder member between an access position and a storage position; at least one guide arm, operatively connected between said mounting and said articulation joint, to guide movement of said second ladder member as said drive means moves said first ladder member; whereby, said drive means is configured to be operated by a user to control the operation of said access device between the access position and the storage position, in which, in said access position, each of said first and second ladder members (5,6) are substantially coaligned and extend substantially outwardly and downwardly from said elevated surface, and, in said storage position, each of said first and second ladder members (5,6) are retracted in a substantially vertically disposed manner substantially atop said mounting pivoted relative to each other from the access position; a rotatable member having first, second, and third pivotal connectors (21, 22, 23) spaced apart in a triangular arrangement; the first connector being pivotally attached to said mounting; the second connector being pivotally attached to said first ladder member via a control arm at a second pivotal connection; and the third connector being pivotally attached to an upper extremity of said mounting via an extendible arm; the third connector is disposed outwardly of the first and second connectors (21, 22), the first connector is disposed inwardly of the second and third connectors (22, 23), and the second connector is disposed upwardly of the first and second connectors (21, 23).