The Sierra Club, Colorado’s largest grassroots group committed to protecting our air, water, land and people, has voted to endorse Proposition 110. Why are we weighing in on transportation? Well, the cars and trucks we drive (and getting the oil and gas that power them) is the largest source of air pollution in the metro area, and one of the largest sources of greenhouse gas emissions. In order to reduce pollution, we need to switch to cleaner cars and electric vehicles – but we also need better transportation infrastructure that gives us more options in how we travel, and lets us spend less time stuck in traffic. That’s where Proposition 110 comes in.