The problem with petroleum used for transportation is that it is easy and cheap. Don Firth's post- the need for plastics in one hell of a lot of our goods (my keyboard as I type this as well as all those ballpoints we dump in drawers that have been sent out with duns for donations, the bottle my milk comes in, many items around the house and now a major component in the wings for the new Boeing people carrier)- is one factor that may cut petroleum use as a fuel.

Reserves economically feasible will last at least 50 years; hopefully measures will be taken to find substitutes before then.

China with their one child policy did cut population growth, but now they have the beginnings of a problem of a lot of oldsters with no young to support them, necessitating extensive and expensive care facilities, etc.
China is building extensive nuclear energy facilities to supplant inefficient power plants dependent on coal (and oil), and is now the biggest user of solar panels to supplement home heating and other small needs.
Admittedly a big source of 'greenhouse' gases, toxins and black carbon, perhaps China, for all its size, will become the leader in reducing materials that harm the environment.
Petroleum for energy generation and plastics will continue to be important to their economy for many years, hence their new gas pipelines and lease bids in Iraq and elsewhere (Like the U. S., new or increased pipelines from Canada and the Arctic, and continued exploration and bidding for sources.

I cannot see people willingly reducing standards of living, nor will they elect leaders that will enforce reductions. Education leading to use of more efficient substitutes for high-pollution sources is needed now.