Building Greener CitiesCities are one of mankind's greatest inventions, they bring us together and drive wealth; but as more people flock to live and work in cities, we need to find ways to make them greener, more sustainable, and more efficient places to live. In this program, physicist Dr. Niraj Lal explores some of the engineering solutions driving change. He visits the construction site of the largest public transport system ever undertaken nationally and discovers how engineers are finding ways to replace concrete — one of the biggest CO2 emitters in the world — with greener alternatives.