For some residents of Bogotá, Colombia, taking public transport used to be a three- to four-hour exercise in frustration. Then the city did something incredible: Instead of investing in a wildly expensive subway system, officials commandeered two to four traffic lanes in the middle of major boulevards, isolating them with low walls to create wide "tracks" for a new bus system. Those trips that used to take hours now only take 40 minutes.

Called "TransMilenio", the bus rapid transit system is now used an average of 1.6 million trips each day. That's more people per mile every hour than almost any of the world’s subways. According to the NY Times, this has allowed the city to remove 7,000 small private buses from its roads, reducing the use of bus fuel — and associated emissions — by more than 59 percent since it opened its first line in 2001. From the article:

Subways cost more than 30 times as much per mile to build than a B.R.T. system, and three times as much to maintain. And bus rapid transit systems can be built more quickly. “Almost all rapidly developing cities understand that they need a metro or something like it, and you can get a B.R.T. by 2010 or a metro by 2060,” said Walter Hook, executive director of the Institute for Transportation and Development Policy, in New York.
Last year, in recognition of their system and its benefits to the environment, the United Nations designated TransMilenio as the only large transportation project approved to generate and sell carbon credits. This has already benefited Bogotá to the tune of $100-$300 million. 

Obviously, this sounds like a really effective system for cities that do not have the funds or infrastructure for a subway system. One additional nice impact is that Bogotá's system removed a great deal of downtown parking to make room for the buses, forcing some car-owners into the system. This, and a new alternate-day driving restriction determined by license plate numbers has worked to remove even more vehicles from the roads. 

Check out the full article here.