The starting point for this discussion is the paper "Towards green mobility: the evolution of transport"
Fig 5 in this paper (Gruebler[1]) presents data for the rates of growth of major components of the US transport infrastructure. It shows that the pattern of growth follows a regular pattern and the conjecture is that an emerging technology will follow the same pattern.
I have taken this figure, reconstructed the underlying equations and extrapolated a curve for a "new transport technology" which I have labelled Automated Transport in Fig 1.
Fig 1
Note that although the examples given in the original figure shows successive technologies emerging at regular intervals, this does not mean that a major new technology has to emerge.
Gruebler identifies Maglev as a potential contender but I do not see this as the key emergent transport technology. I suggest a better contender would Integrated Automated Transport as an inclusive term that includes MagLev, Automated Mass Transit, PAT and MAIT. This could be argued to be well on its way with a considerable length of ATM guideway already installed.
PAT or MAIT could be chosen, with the effect of moving the bell shaped curve to the left by a decade or so. Maybe it does not matter, the important lesson is that the "new transport technology", whatever form it takes, will take some decades.
Fig 2
My thesis is that Integrated Automated Transport will become the predominate form of transport, displacing roads. However, we see from Fig 2 that we should expect it to reach about only about 10% of its potential by 2040.
Integrated Automated Transport is expected to reduce energy demands by a considerable factor, and at the same time allow the use of renewable sources to be used. Thus it is offers a badly needed fix to the need to reduce global carbon emissions, but it is not a quick fix.
Even though Integrated Automated Transport is the long-term solution, reducing pollution in existing transport still remains a vital medium term objective.
[1] A. Gruebler (1990) The Rise and Fall of Infrastructure: Dynamics of Evolution and Technological Change in Transport (Heidelberg: Physica)