This paper presents a synthesis of two decades of ridership forecasts developed for proposed high-speed intercity passenger rail (HSR) routes in various stages of development across North America. A comprehensive database of ridership forecasts consisted of 210 ridership estimates from 43 unique intercity corridors. Analysis of the database revealed that increasing the maximum operating speed of the HSR service increased ridership, and a simple multiple linear regression model yielded demand elasticities that were consistent with values reported in published rider-ship studies. Regarding the impacts of HSR on the broader transportation system, this synthesis found that the mode share of HSR as well as the percentage of airline trips diverted to HSR services increased as the maximum speed of the system increased. The percentage of induced trips and the percentage of automobile trips diverted to HSR did not vary significantly with speed. Whereas this synthesis provides a starting point for a broader discussion about the importance of ridership forecasting in the development of the U.S. HSR network, each intercity corridor being considered for HSR service is unique, and market-specific ridership studies should be undertaken to identify the various ridership and other metrics necessary for service development. Improvements to the forecasting process, including greater transparency in the forecasting metrics reported as well as post facto evaluation of the ridership forecast against actual passenger traffic, would benefit the entire HSR service development process.