Peak Car is more likely to be related to an automotive-ownership saturation level given a particular configuration of wealth, age and other demographic components. In countries such as the US and UK and Australia that number hovers around .7 (700/1000 pop) and is currently flat. Some hope it will climb given an economic recovery, some pray for permanent decline or at least continued stagnation. It does make sense that there would be a ceiling to automotive use—at least on a per capita basis. And something under .75, given the portion of a population under driving age or over driving capability, seems reasonable (as a guess, I mean, not for our cities).
Regardless of where such a ceiling might be, the rest of the world, (especially China) still wants to get to that lofty place. (more china news re traffic) Hence Two Billion Cars is the near-term prediction, hoping and praying aside. If the Sperling-Gordon "doubling" prediction is off the mark, it will be off only by a couple of years.
Most of us think only about our car or the cars in our neighborhood or city. But the matter of automobility is much larger as it addresses a critical human and urban need. Wishing it would get fixed or go away won't make it so. You may personally have more or less use for an automobile. You may arrange your life to use very little or over much. But world vehicle population will double—likely in less than 20 years.