Transit ridership measures the number of trips taken on public transit, a key indicator of transit system performance and community transportation patterns. Federal interest in transit ridership connects to climate policy—increasing transit use reduces transportation emissions by shifting trips from private vehicles. Federal transit investments often aim to increase ridership through service expansion, quality improvements, and fare affordability. Ridership data helps justify funding requests, evaluate service changes, and plan network improvements. Ridership levels affect transit operating revenue since fares represent significant income. COVID-19 significantly reduced ridership, with recovery ongoing. Factors affecting ridership include service frequency, coverage, reliability, safety, comfort, fare levels, and competition from other transportation options including driving and ride-sharing.