“ In these circumstances, we find no basis for holding that the local school authorities may not be required to employ bus transportation as one tool of school desegregation. Desegregation plans cannot be limited to the walk-in school.
'An objection to transportation of students may have validity when the time or distance of travel is so great as to either risk the health of the children or significantly impinge on the educational process. District courts must weigh the soundness of any transportation plan in light of what is said in subdivisions (1) , (2) , and (3) above. ”

“ The school system was operated under a geographical attendance zone system, with freedom-of-choice transfer provisions for all students regardless of race.
Prior to this Court's holding in Swann v. Charlotte-Mecklenburg Board of Education, 402 U.S. 1, 91 S.Ct. 1267, 28 L.Ed.2d 554 (1971) , the plaintiffs submitted a plan devised by their consultant, Dr. Larsen; it was designed to achieve as closely as possible a mathematical racial balance in all of the schools of the system equal to that in the system as a whole. It employed satellite zoning and extensive cross-busing. ”

“ The school authorities, declaring that they considered themselves 'required' to do so, adopted a revised pupil assignment plan which was expressly designed 'to achieve a racial balance throughout the system which will be acceptable to the Court.' (Emphasis added.) Prior to the adoption of the revised plan, the school system transported about 18,000 pupils per day in about 216 buses. The drafters of the revised plan estimated that it would require at a minimum, with use of staggered school openings, 157 additional buses to transport approximately 16,000 additional pupils. ”

“ Respondents, who are Negro pupils and parents in the school system, commenced action alleging that the School Board was operating a dual school system, and seeking appropriate relief. The school system embraces both rural and urban areas in a county school system. The District Court found that in December 1969 there were 67 schools in the system with approximately 50,000 students. The total student population was 72.5% white and 27.5% Negro. ”

“ The application for stay is further weakened by the absence of specific allegations as to the time of travel or other alleged hardships involved in the added bus transportation program. Specific reference to the travel time in relation to the age and grade of particular categories of students is not disclosed. ”