Oregon and Washington want desperately to build a new bridge across the Columbia River, near Vancouver, to ease congestion. (Cost ~ $2.4B.) But, being Oregon and Washington, they want to decrease greenhouse gas emissions, too. In fact, Governor Kulongoski (D-OR) wants to decrease them by 75% by 2050.
So word has come down to factor emissions into the bridge planning process.
This completely misses the forest for the trees.
The difference between building a bridge and not building a bridge is only about 5,000 cars a day--fewer if the bridge is built. (I'm not exactly sure how about this conclusion--why are there fewer cars if the new bridge is supposed to ease congestion--but let's accept it for now.) There will be about 175,000 daily trips across the bridge, on average, by 2030. So the difference is about 3%.
Considering that this bridge and its associated commute will represent only a very small fraction of the total greenhouse gas emissions of Oregon and Washington, and that transportation only represents about 30% of all GHG emissions, the difference between building a bridge and not building a bridge is a small fraction of one percent. It's not worth worrying about.
If we are truly going to meet Kulongoski's goal, we need vast and comprehensive changes in our society. Whether we built this bridge or not will make little difference, especially if it primarily carries cars instead of bicycles, buses, scooters and light rail.
People have still not grasped the enormity of what's required to avoid significant global warming of even a couple of degrees. We must, almost literally, reinvent civilization. That's a lot more than just bridges.