Designing for the edges improves the center

In 1990, the Americans with Disabilities Act mandated curb cuts at intersections across the country. The requirement was specific: Wheelchair users needed a ramp from sidewalk to street. What happened next was probably unexpected. Cyclists used the cuts. Parents with strollers used them. Delivery workers with hand trucks. Travelers with rolling luggage. A design solution created for a specific need ultimately became the standard for everyone, because it addressed a real human constraint instead of an imaginary “average” user. Nobody who has ever rolled a suitcase down a city block thinks of...