Traffic on the Avenue de la Grande Armée in Paris. (Stefano Rellandini/AFP via Getty Images) BARCELONA — In an effort to ease traffic congestion and curb greenhouse gas emissions causing climate change, municipalities from Barcelona to Brussels have embarked on what has been called “a transportation revolution.” Urban centers across the continent have adopted a host of innovative schemes designed to steer vehicles out of crowded downtowns, creating so-called 15-minute cities — where cars aren’t needed and services like banks, barbers, grocery stores and doctors are a short stroll or bike ride away. But a fierce backlash has emerged in...