Beyond the Surface: Why Cities Invest Billions in Subways to Solve Congestion, Climate, and Land Use Crises

The concept of grade separation—separating the train line entirely from all other traffic, usually by tunneling—is the operational genius of the subway. This separation is non-negotiable for true rapid transit, as it eliminates every single point of conflict, from pedestrians to cars and buses. Once liberated from the unpredictability of surface traffic, the train can maintain high speeds, high frequencies, and, critically, near-perfect punctuality, regardless of what is happening above ground.