Black cabs are limited in number due to the difficulty of the Knowledge test. Ubers aren't limited in number and Uber makes no effort to discourage excess drive

Black cabs are limited in number due to the difficulty of the Knowledge test. Ubers aren't limited in number and Uber makes no effort to discourage excess drivers from logging on. (If it reduces the average wait by 10 seconds, it's worth it in their eyes, as it costs them nothing. The congestion cost is externalised.) Uber also sends push notifications to drivers to go to specific areas to prevent surge pricing.