&gt; A full van is more space efficient than 12 bikes.<p>Arguable, but buses are higher density than vans, trains are higher density than buses, and subways aren&#x27;t subject to traffic.<p>The bicycle isn&#x27;t in competition with the subway, it&#x27;s in harmony with it.<p>&gt; She&#x27;d just share the ride with more people. This is exactly what a subway would do, except without the need for expensive infrastructure.<p>I don&#x27;t think if you extrapolated the current ridership of BART just for people traveling within San Francisco that you would find it practical to run buses for all of them, and when a vehicle on the ground during rush hour (including buses) is rarely moving more quickly than a typical pedestrian, the subway has an obvious advantage.<p>You can try to traffic engineer all day, but the fastest route between two points on earth is through the earth. :)