The X4TM Rail Edition. Built upon the proven X2TM Rail Edition, the X4 Rail Edition sets the bar even higher as the new industry standard for refrigeration performance and efficiency. Engineered for durability and tested to withstand the rigors of intermodal and rail duty. Ultra high efficiency provides lower cost of ownership. The practical design and innovative engineering results in lower fuel consumption, reduced engine runtime and lower maintenance costs. Ultra high capacity. The X4TM Rail Edition provides fast pulldown and precise temperature control.