I find the studies on mobility and air quality very interesting. As you know, the city of Mexico faces a very strong traffic problem, which has resulted in an increase in the level of air pollution. the TomTom index (attached) says that we are the city with the most traffic in the world!!
I believe that one of the solutions is the investment in public transportation of quality that encourages people to no longer use the car so much. however, in the economic studies on mobility, 2 opposing effects are stipulated (attached you can find a paper on this):
The “traffic creation effect” stipulates that the introduction of a new public transport can increase economic activity in the nearby area, which would mean that people who previously did not frequent that area now did so. For example, people who got a new job in that area. This would generate a new demand for trips to this area of the city, however, this new demand can be met by both new public transport and private cars and, in case more people opt for transport in cars, the level of congestion would increase and, therefore, also the level of pollution (i think that Santa Fe can be a good example).
On the other hand, with the introduction of a new mode of public transport, travelers who previously depended on private means can now change to the new mode. This substitution of the private travel mode to the public is called the “traffic diversion effect”. Ceteris paribus, the effect of traffic diversion should reduce the overall level of vehicle emissions and consequently reduce air pollution.
As you know, in Mexico City there are 12 subway lines and the expansion of line 9 and 12 (which ended in 2019) is in process, so, my question is: which of the two effects do you think it will win in the long-term? Do you think people who use the car in Mexico City are willing to leave it to use public transportation?