THE ? WILLISON AUTO coupler has been used in the Australian sugar cane industry since the mid-1960s. The industry has seen the introduction of not only larger cane wagons of 10?15 tonnes but more powerful locomotives and longer rakes, which has led to operational issues with cane wagon couplings. The ? Willison couplers have experienced increased rates of fatigue failures at the head shank. Over the years the ? Willison couplers had adopted design features of coupler yaw restraints and springs to mitigate instability, leading to jack knife derailment. Yaw restraints are detrimental, though, to longer 10?15 tonne wagons, where greater coupler angles are needed for the negotiation of curves. This paper presents background literature on long train derailment modes from the rail industry. The background explains why the new Bradken design BK49 auto coupler makes use of a frictional yaw restraint in place of spring restraints. Other aspects of the coupler design enhancement are also presented. The BK49 auto coupler has been developed to provide interoperable replacement of ? Willison couplers and also has the capability to replace the ? Willison/loco couplers. The coupler strength is more than twice that of the older version Willison couplers. The resulting expected fatigue life improvements are anticipated to exceed wear life and potentially simplifying the inspection regime. The frictional yaw restraint in buff loading has controlled the risks of jack knifing from lateral instability of the coupler. The BK49 auto coupler provides 15 degrees rotation for yaw to improve curve negotiation of long vehicles. Clearance for socket heads on the mounting bolts also speeds maintenance with a more robust vulcanised rubber buff pad reducing operational costs.