Freight exchanges are central to the logistics industry, as they reduce empty runs and meet spot demands. To improve their efficiency in terms of automation and enhance trust between the participants, we propose a decentralized freight exchange implemented using public blockchains. With our solution, we also address shortcomings of public blockchains, such as scalability and privacy. We present two artifacts: a general architecture for an electronic logistics marketplace (ELM) and a concrete implementation as the proof of concept for a freight exchange. The solution is implemented using two off-the-shelf public blockchains and a public distributed file system. Additionally, we investigate the implications for the general ELM model and show that an ELM based on a blockchain can be viewed as infrastructure rather than a market participant.