Improvements in plastic recycling technology along with pressure to reduce emissions and waste has led to a desire to find environmentally friendly, cost competitive railway sleepers. This study conducts life cycle analyses of emissions and costs for timber, concrete, short fibre and long fibre composite railway sleepers to determine which sleepers are more environmentally friendly and cost competitive. The results clearly highlight the environmental advantages of short fibre plastic composites. The basic scenario had concrete sleepers being the most cost competitive, before factoring in the recyclability and likely future cost reductions of short fibre composite sleepers. With as little as 50% of the entirely recyclable short fibre sleepers being recycled their cost quickly becomes comparable to concrete sleepers. Further, there are several likely changes in the future that will make short fibre sleepers even more cost competitive. The short fibre industry is still growing and could substantially reduce costs through the effects of economies of scale and experience curves of production. A further driver of future cost competitiveness would be the broader use of an Australian or international carbon price, where concrete sleepers have a disadvantage. Together, these changes indicate that short fibre composites have great potential financially and environmentally.