Technological stabilisation

I have been reading recently about the possibility of a Technological Singularity. There are some impressive graphs showing the rate of change of technology. This is certainly interesting, but I am a little skeptical. If we look one variable of technology, the speed of the fastest public transportation (see graph below), we find that this has actually dropped and plateaued in recent years. The reasons for this are: physical limits (the sound barrier) and associated costs; demand (you can get all the way around the Earth in 24h). There is a maximum acceleration that the human body can tolerate, which will dictate speed in the long term (until we enhance or transcend our biological existence, develop warp or develop wormholes).