I wish greenies would get more objective. The Treehugger blog rails at every indignity to the environment in a loud voice. But which green projects are highest priority?
A bus is better than a personal vehicle, but BEST OF ALL are subways and commuter trains.
I’ve never used the Moscow subway system, but have always heard it was great. Mexico City is a dream. You can get anywhere quickly and easily.
Here are diagrams of the two excellent transportation systems:

from subway systems of the world – Fake is the new real
Big cities singled out for terrible train service: Beijing, Toronto.
(But Beijing is making big plans.)
In my town we have the LRT (Light Rail Transit) and it is fantastic — IF you can get to and from the train by foot, bike or bus.
The first thing I would do for the EARTH here is build more LRT capacity.
Then improve the bike trails to get to the LRT stations.
Everyone agrees, in theory. But when it comes to approving the capital cost of new train capacity, we get balkers. (Decision makers drive to work in big personal vehicles.)
But trains really are the most cost effective transport:
LRT cost efficiency improves dramatically as ridership increases. the Calgary, Alberta C-Train used many common light rail techniques to keep costs low, including minimizing underground and elevated trackage, sharing transit malls with buses, leasing rights-of-way from freight railroads, and combining LRT construction with freeway expansion. As a result, Calgary ranks toward the less expensive end of the scale with capital costs of around $24 million per mile
However, Calgary’s LRT ridership is much higher than any comparable U.S. city at over 250,000 rides per weekday and as a result its efficiency of capital is also much higher. Its capital costs were ⅓ that of the San Diego system, a comparably sized one in the U.S., while its ridership is well over twice as high. Thus, Calgary’s capital cost per weekday rider is less than 1/6 that of San Diego. Its operating costs are also lower. A typical C-Train vehicle costs only $163 per hour to operate, and since it averages 600 passengers per operating hour, [18] Calgary Transit estimates that its LRT operating costs are only 27 cents per ride, versus $1.50 per ride on its buses.
Cost – Wikipedia
Needless to say, Calgary Transit charges riders C$2.25 for a ticket on either LRT or bus. We have plenty of buses driving around town empty.
(via Treehugger)

Calgary Transit
Lest I come off too enthusiastic about Calgary Transit, let me add I’ve found them arrogant, wasteful idiots for the most part. But they have done a good job with the LRT.