The old vacuum trains that are designed to remove trash from the tracks are ineffective and often broken. A 2016 study by Travel Math had the New York City Subway listed as the dirtiest subway system in the country based on the number of viable bacteria cells. In August 2016, the MTA announced that it had initiated Operation Track Sweep, an aggressive plan to dramatically reduce the amount of trash on the tracks and in the subway environment. This was expected to reduce track fires and train delays. As part of the plan, the frequency of station track cleaning would be increased, and 94 stations would be cleaned per two-week period, an increase from the previous rate of 34 stations every two weeks. The MTA launched an intensive two-week, system-wide cleaning on September 12, 2016. Three new powerful vacuum trains were later ordered; one arrived in 2018, and the others are expected in 2019. The operation will also include 27 new refuse cars.