Railways in several countries are now operated through open access competition. In principle this allows for anyone to run train services at any time, although in practice a process is needed to coordinate and prioritise between requests, especially if capacity is scarce. Central to this process is usually a national infrastructure agency, which coordinates and prioritises according to some process framework, including explicit or implicit prioritisation criteria. However, such frameworks are often insufficient to differentiate between competitors in an open-access environment, where two or more operators may wish to offer similar services on the same line at the same time of day. An allocation method that improves social welfare would be desirable, but more exact calculations of the welfare contribution of individual departures is probably unfeasible in a deregulated environment, as they require commercially sensitive information such as number of passengers, fares and cost structures.