Dr. Mitch Katz rides his bike to work, defying the commuting norm in Los Angeles. Michael Wilson/L.A.County Health Services Dept. hide caption

itoggle caption Michael Wilson/L.A.County Health Services Dept.

Miramonte Elementary School in Los Angeles. Krista Kennell /AFP/Getty Images hide caption

itoggle caption Krista Kennell /AFP/Getty Images

Back on the road: Traffic on a 10-mile stretch of I-405 in Los Angeles started flowing on Sunday, nearly a day earlier than planned. Kevork Djansezian/Getty Images hide caption

itoggle caption Kevork Djansezian/Getty Images