NPR's Joseph Shapiro recently got a first hand look at what it means to be disabled when he broke his ankle and had to use a four-wheeled scooter to move around. He found that even on the streets of Washington, D.C., where improvements have been made to accommodate the disabled, life can be difficult. He takes a tour of downtown with disability advocate Lisa Iezzoni. Read excerpts from Iezzoni's book, When Walking Fails.