Every time I hear the government say they are going to expand roads or construct metros in the city, there are some activists who are against felling of trees. I understand their concern, but that's merely an outburst rather than a solution.

There is no option but to expand the infrastructure of a city to accommodate the growing population, most of whom are migrating to cities (Especially in India)

Either we cut down trees and build roads/metros or we face the repercussions of insufficient infrastructure. Traffic jams, pollution become inevitable. 

One thing we have to understand is we cannot have it both the ways. If you complain about disturbing nature, you cannot also complain about lack of proper infrastructure, traffic jams, pollution, etc.

I think the solution for a sustainable life is possible only through population control.

No one is talking about it or at least in a serious tone. You might wonder why it is so. If you are not already aware, the world is run by economic forces. Growing population is good for the economy. Unless the governments decide to do something, population control will not be considered seriously.

Once you have more people, you cannot tell that you will not serve them. Governments will be bashed left & right if they do that.