According to the Federal Program Guidance on Safe Routes to School:
Infrastructure projects constructed with these funds [federal aid funds] must be accessible to persons with disabilities, per the Americans with Disabilities Act Accessibility Guidelines (ADAAG) at 28 CFR Part 36, Appendix A, as enforced by the U.S. Department of Justice and FHWA, and as required under Section 504 of the Rehabilitation Act.
Also, this requirement is captured in the overarching purpose of the federal Safe Routes to School program:
(b) PURPOSES.--The purposes of the program shall be-
1. to enable and encourage children, including those with disabilities, to walk and bicycle to school;
2. to make bicycling and walking to school a safer and more appealing transportation alternative, thereby encouraging a healthy and active lifestyle from an early age; and
3. to facilitate the planning, development, and implementation of projects and activities that will improve safety and reduce traffic, fuel consumption, and air pollution in the vicinity of schools.