In 1987, five States were chosen to be included in the HSIS: Illinois, Maine, Michigan, Minnesota, and Utah. The primary criteria used in selecting the States were data availability (the range of data variables collected), quantity, and quality. In 1995, California, North Carolina, and Washington were added to increase the amount of data available and to provide better geographic coverage. In 2002, Ohio was added to the system. In 2002, Ohio joined HSIS to provide additional curvature and grade inventories. Data from the Charlotte, NC, urban area were added in early 2011.
The HSIS laboratory is a virtual laboratory managed by FHWA and staffed by contractor analysts and research assistants.