A SEMI-TRAILER

A semi-trailer (1) has a front gooseneck part (6). A folding bolster assembly (7) comprises a pair of support arms (35) pivotally mounted on the front gooseneck part (6) for movement between a folded stored position inboard of sides (30,31) of the trailer body (2) and an in-use position projecting laterally outwardly of the trailer body (2) for engagement with and support of a container mounted on the trailer body (2). When the folding bolster assembly (7) is in the folded position a 45 foot container can be mounted on the semi-trailer (1) and when in the in-use position a 40 foot container can be mounted on the semi-trailer (1).