Many others have asked this same question. The National Center for Safe Routes to School--which is located within the University of North Carolina's Highway Safety Research Center--is a federally-funded information clearinghouse for the federal Safe Routes to School (SRTS) program. We at "the National Center" provide technical assistance to State SRTS Coordinators, and professionals working to implement SRTS programs at more local levels of government. We also provide training to transportation and health professionals on matters related to SRTS, and we offer a free data collection and reporting service to local communities who want to understand the impacts of their SRTS programs.
The Safe Routes to School National Partnership, on the other hand, is an umbrella advocacy organization that is comprised of a network of more than 600 nonprofit organizations, government agencies, schools, and professionals with a common goal of advancing the Safe Routes to School movement in the United States.
Because the National Center's relationship with the National Partnership is not readily apparent, we've developed a resource that describes our two agencies' relationship, as well as how we work together with federal and state departments of transportation to advance SRTS. The resource is entitled, Working Together to Advance Safe Routes to School.