As of December 4, the San Francisco County Transportation Authority has released the Draft Final Report of its Mobility, Access and Pricing Study (MAPS). I will critique this report over my next few blogs.
There is also a overview video here, whose cover frame is overlaid with the news-byte: “Private automobiles contribute over 45% of greenhouse gas emissions.” The number generally quoted for this is closer to 33% – i.e., transportation, of which the private automobile is only a fraction, contributes about a third of GHG emissions, so that I had always understood the private automobile to be responsible for between a sixth and a quarter (depending on several other factors). In any case, in the interest of determining how this number became inflated, I note that on page 1-8 (figure 1-4) the combined contribution of the Intraregional Road Vehicles plus the San Francisco Road Vehicles is 47%.
So the cover statement on the video should probably read: “Cars and trucks in the San Francisco area contribute over 45% of greenhouse gas emissions.” The misquote unnecessarily demonizes the automobile.
Still… how did the more typical number quoted as 1/3 become nearly 1/2? The reason is at least four-fold. First, the 47% number is from 20 years ago and engine efficiency has helped to slightly lower the relative contribution of the internal combustion engine of the private automobile since then. Second, the principle forms of commence in the Bay Area would tend to make the internal combustion engine a larger relative contributor than say would be the case with refinery-heavy New Jersey (which of course leaves some of San Francisco’s road-filth on the east cost and uncounted in the 47% figure, which means 47% might even be conservative!). Third, San Francisco has greater than average congestion (for the US), which would also raise the local relative contribution of vehicular GHGs. Fourth, San Francisco, due to its latitude, needn’t heat its homes as much as more northern mega-regions, hence lowering the relative contribution of buildings re GHG emissions in the case of San Francisco.
So, the ‘over 45%’ number is indeed believable – and alarming – and says that the solutions proposed (including congestion-pricing) may be as important for San Francisco as for any US city. It may be that the case for congestion pricing in San Francisco is stronger than it was for Manhattan.
Next: Plan Details.