- Fulvio Amato and Teresa Moreno, Spanish Scientific Research Council CSIC
- Read Time: 5 mins
Subways are vital for commuting in crowded cities, something that will become more and more important over time – according to a United Nations 2014 report, half of the world’s population is now urban. They can also play a part in reducing outdoor air pollution in large metropolises by helping to reduce motor-vehicle use.