At 12:15hrs Truck 21 was dispatched to assist MCFRS with a reported vehicle off the beltway overpass with fire. Upon arrival of Ladder 32 a large roll-on dumpster transport was found to have struck the beltway wall, went over the side and landed on the feeder road area becoming fully involved in fire. Upon arrival of Truck 21 the crew provided additional water supply to Ladder 32 to support Class B foam operations. Upon completion of support assignments Truck 21 returned to service.