This article says that Toyota will soon introduce plug-in hybrids. It claims that these vehicles will be able to travel up to 10 miles on just their electric battery and then each night they would be recharged. So, this means that urban drivers could sharply increase their vehicle's fuel economy and presumably also reduce their smog emissions. Per mile of driving how much will CO2 emissions decline by? This hinges on the average power plant's emissions factor. If California goes ahead with its aggressive RPS standard then the electricity will be getting greener at the same time that more of the vehicle fleet will be running on electricity.
Suppose that 100% of the California vehicle fleet runs on electric power. If each of the 20 million vehicles runs on electricity and travels 12,000 miles each; how much extra power will be needed to travel this 240 billion miles? California is going to need to site a lot of new generation capacity. Which suburban communities will forget about NIMBY issues? Where will transmission lines be sited? Will ecologists battle the energy generation community over where to site these needed facilities?
It is clear to me that the introduction of the Plug-In hybrids will certainly help to meet the Pavley fuel economy standards. A small share of the fleet (if it achieves 250 MPG) can help to meet this average standard.