A trailer comprising: a trailer body (102, 202)having a front end and a rear end; primary wheels mounted under said trailer body (102, 202) closer to said rear end than to said front end and in contact with the ground for supporting said trailer and allowing said trailer to be towed in a travel direction; an adjustable leg (108, 208) mounted under said trailer body (102, 202) closer to said front end than to said rear end for providing secondary support of said trailer while said trailer is being towed, said leg comprising a terminal end (114, 214) moveable between a retracted position and an extended position, and a secondary wheel rotatably attached to said terminal end (114, 214) of said leg (108, 208) for rotation in said travel direction such that said secondary wheel is off the ground when said terminal end (114, 214) is in said retracted position and is in contact with the ground when said terminal end (114, 214) is in said extended position, and said secondary wheel is operable to support said trailer while said trailer is being towed in said travel direction; a pneumatic or hydraulic drive unit mounted on said trailer body (102, 202) for adjusting said leg (108, 208) to move said terminal end (114, 214) of said leg (108, 208) between said extended and retracted positions, said drive unit operable to move said leg (108, 208) between said extended and retracted positions while said trailer is being towed; a drivetrain mounted on said trailer body (102, 202) and operatively connected to said secondary wheel for driving said secondary wheel; a controller for controlling operation of said pneumatic or hydraulic drive unit to automatically adjust said leg (108, 208) to maintain balance of said trailer while said trailer is being towed, and for controlling operation of said drivetrain to drive said trailer when said secondary wheel is in contact with the ground. a trailer body (102, 202)having a front end and a rear end; primary wheels mounted under said trailer body (102, 202) closer to said rear end than to said front end and in contact with the ground for supporting said trailer and allowing said trailer to be towed in a travel direction; an adjustable leg (108, 208) mounted under said trailer body (102, 202) closer to said front end than to said rear end for providing secondary support of said trailer while said trailer is being towed, said leg comprising a terminal end (114, 214) moveable between a retracted position and an extended position, and a secondary wheel rotatably attached to said terminal end (114, 214) of said leg (108, 208) for rotation in said travel direction such that said secondary wheel is off the ground when said terminal end (114, 214) is in said retracted position and is in contact with the ground when said terminal end (114, 214) is in said extended position, and said secondary wheel is operable to support said trailer while said trailer is being towed in said travel direction; a terminal end (114, 214) moveable between a retracted position and an extended position, and a secondary wheel rotatably attached to said terminal end (114, 214) of said leg (108, 208) for rotation in said travel direction such that said secondary wheel is off the ground when said terminal end (114, 214) is in said retracted position and is in contact with the ground when said terminal end (114, 214) is in said extended position, and said secondary wheel is operable to support said trailer while said trailer is being towed in said travel direction; a pneumatic or hydraulic drive unit mounted on said trailer body (102, 202) for adjusting said leg (108, 208) to move said terminal end (114, 214) of said leg (108, 208) between said extended and retracted positions, said drive unit operable to move said leg (108, 208) between said extended and retracted positions while said trailer is being towed; a drivetrain mounted on said trailer body (102, 202) and operatively connected to said secondary wheel for driving said secondary wheel; a controller for controlling operation of said pneumatic or hydraulic drive unit to automatically adjust said leg (108, 208) to maintain balance of said trailer while said trailer is being towed, and for controlling operation of said drivetrain to drive said trailer when said secondary wheel is in contact with the ground.