I do think 21t century technology will continue to make our mass transportation more widely available. Our technology is attracting more and more people to come our way, and this would mean the need for more transportation. I also feel smart phones play a role in transportation availability as well.
With the new technology in the twenty first century, we will have the ability to make mass transportation better and more accessible. We would need to do that if we are going to cut back on emissions and make our planet a better place to live. So it is good if this would happen.
Modern technology such as maglevs, air tubes and electromagnetism will make mass transit faster and safer. When trains or monorails can move as fast or faster than airplanes, ground transport will become the norm instead of the exception. Ground transport is safer in that if something goes wrong, no one plummets 20,000 feet to their deaths. Constructing and maintaining such systems creates thousands of jobs. Mass transit improves the quality of life for humans and helps prevent carbon emissions caused by jet fuel.
In an effort to help control the environmental impact of cars, hopefully we will all be more willing to engage in using mass transportation as time goes on and, especially, if cities become more congested, as we have seen with New York City. However, it really depends on where a person is living. In some cases, it can be wasteful for mass transportation, such as for those who live in small towns. Unless a population is congested in a smaller area, it's doubtful that mass transportation will really catch on and, since it isn't likely all cities will be like New York City during this century, I doubt it will happen in the near future.
Unfortunately, although 21st century technology may improve mass transportation, it is not likely to be responsible for it being more widely available. The reason for this is that the biggest issue most communities face in making mass transportation widely available is cost. It is expensive to run extensive lengths of rail or monorail tracks, for instance, which has little to do with technology, but the acquisition of land, the hiring of workers and maintenance.