Seattle's Children's Hospital and Regional Medical Center could get more employees out of their cars, significantly easing the traffic effect of its proposed expansion, according to a study. Just under 38% of daytime Children's Hospital employees now drive alone to work, and hospital officials have proposed a program they say would lower that rate to 30% during a proposed expansion that would more than double the number of beds and building sizes on the hospital's 22-acre campus and the 1.8 acres facing it.