Originally Posted by makeinu

It is low. If you read the source there are a number of things to consider:
1. It is not a true percentage of greenhouse gas emissions, but rather a percentage of the "global warming potential". The difference is that the "global warming potential" is a weighted sum rather than an unweighted sum. So carbon dioxide counts more, for example, than methane or nitrous oxide.
2. Fossil fuel production and distribution is not included. This is another 11.3%. Since most fossil fuels are used for transportation, I think the total impact of transportation fuels from well to atmosphere should be more like 25%.
3. These are worldwide emissions. Most countries' automobile usages aren't nearly as high as the US. I'm willing to bet that if this data were for US only then the number would jump from 25% to 50%.

I also wonder how much of the emissions attributed to "industrial processes" comes from car manufacturing.