It's frustrating to see another technology possibly go the way of nuclear for the sake of politics and optics, when the tools to remediate emissions exist. Granted emissions expenses for diesel are at first blush several times that of petrol engines, but a full comparison would include a) at least 25% greater carbon tax on petrol and b) gasoline particulate filter cost for complying with forthcoming PM2.5 regs for petrol engines, esp. the GDI engines so beloved on Audis.