Physics and Transportation Speed
As is well known, the increase in transportation speed characteristic of most of the 20th century came to a halt a few decades ago. This is usually expressed in terms of “What happened to yesterday's dreams?” or even “What happened to yesterday's reality?” To be more specific, there's the common rhetorical question, “If we could put a man on the moon, why can't we put a man on the moon?” (with similar questions about the Concorde, etc.).
From a physics standpoint, you can think of speed as proportional to the square root of energy divided by mass. Since per capita energy use has continued to increase over most of the past few decades (even if not at the pace of the 1960s) and per capita mass use has, if anything, declined, we should expect speeds to continue to increase.
I suspect the stagnation is more illusion than reality. I think average speeds have continued to increase, but the ability of our society to concentrate energy in just one nation or just one project is disappearing. A couple of decades ago, William Gibson said “The future is already here—it's just not very evenly distributed.” Since then it has gotten better distributed.