Abstract: Railway transportation is a mean of conveying ore, goods or passengers on wheeled vehicles running on rails. The operation is costly and the transported goods have low aggregated value, therefore profitability is enabled under long distances and large quantities. Railways all around the world face rising demand for transportation of goods and people. While upgrading the railroad infrastructure is guaranteed to increase capacity, it usually takes large capital expenditures and is time consuming. In this paper we show how a circulation planning tool can aid railroads fully utilize their infrastructure in order to improve capacity utilization. Parameters such as train departing frequency, behavior during train delays, priorities on the negotiation of crossings and overtakes, performance allowance, and headway can be varied, and the resulting scenarios can be compared to help find a reasonable ceiling to the railroad capacity. The same tool can be used in an operational setting, to quickly respond to incidents and disruptions while keeping services at an acceptable level. There are many publications that propose methods to calculate railway capacity. While traffic simulation methods offer accurate results, user interaction and graphical presentation, they are often time-consuming, so analytical methods are usually preferred. Our simulation approach takes just seconds to run, resulting in a much more powerful tool to assess capacity limits. We run our simulations with data from a real heavy haul railroad, and use a number of metrics to show how their current operation could be improved with no need to build more tracks. Preliminary results indicate that, by changing train departing frequency alone, throughput could increase by more than 20% Ver menos