According to the United Nations, The urban population has more than quadrupled since 1950, by the year 2030, 60 per cent of the global population will live in cities, and as cities and urban centers all over the world grow exponentially The number of people that commute to and from work will also be increased As people spend more time on crowded roads, the loss of time and increased stress negatively impacts the economy, the streets are full of cars and buses with no room to spare.
One solution is to build underground subways. This solution can be applied to almost any city including those with unstable soil, like sand or gravel, with modern construction and digging techniques and machinery, it's possible to build underground tunnes anywhere in the world and at any depth. However, underground trains cost 9 to 10 times as much as light rail, and its construction is significantly slow and more problematic, when building underground there are a miriad of problems that can delay the progress for months, even years.
Also, building underground is extremly expensive, so much that in fact, only developed world cities and others with the help of BMI or the private sector can undertake the challenge.
For the cost of building only two station, you caould build an entire line of 10-15 stations with this system.
Bulding above traffic is a more feasable solution, there are elevated lines in a lot of cities from Chicago to Mexico City to Mumbay, However, the current construction techniques and structures have a negative impact on any street below, the wide tracks block sunlight and immediately decrease the value of properties all around, not to mention that the numerous beams and columns used are almost as expensive as building underground. To make it even worst, the size of the columns/pylons is so big that often takes one or two lanes of the streets below, making traffic worst and therefore negating the very purpose of building elevated tracks.