This dataset is one component of the National Transit Database (NTD). The NTD records the financial, operating, and asset condition of transit systems helping to keep track of the industry and provide public information and statistics. This dataset includes only monthly unlinked passenger trips for each urban transit system in the U.S. Transit systems are separated by type (mode) such as heavy rail, light rail, and bus. "Unlinked passenger trips" represents the number of passengers who board public transportation vehicles. Passengers are counted each time they board vehicles no matter how many vehicles they use to travel from their origin to their destination. More information about the NTD is available at https://www.transit.dot.gov/ntd.