I agree, that's the main barrier. A subway line might cost a few billion, but reorganizing a major urban area to be walkable takes decades.<p>Part of it is that most American cities are very new in comparison to their European and Asian counterparts.<p>London, Paris, Barcelona, Tokyo, Kyoto, Seoul, etc. all have Ancient, Roman and/or Medieval cores which by default are designed for walk-ability. The modern cities are by and large extensions of those cores. The only American cities that have similar levels of walk-ability are ones that were founded and largely settled before the car like New York, Philadelphia, D.C. -- basically mid and north atlantic cities. Otherwise you simply can't walk by design.<p>Fixing that requires essentially rebuilding an entire city, which really isn't going to happen anytime soon. Imagine rebuilding something like say, L.A., at ~500 sq miles of broken sprawling urbanity, to be mass-transit ready.