"It's very simple. Blue buses travel long distances on major arterial roads, serving more than 2 districts, and run in median bus lanes when they get close to the centre of the city (this video shows a blue bus entering a separated median lane). Green buses operate as feeder buses to the 8 lines on the subway system and are run by private companies. Red buses are express routes with limited stops connecting major suburban towns to the central city. And yellow buses are circular routes that travel between the major destinations in the central city. Blue and red buses are the same price, while the red (suburban) buses cost more and the local yellow buses less."