I think it all depends on which you rank as worse - SOx, NOx and unburned hydrocarbons, or CO2 and resource consumption. SoCal has smog problems so rates the first three higher than the last two. The EPA takes its lead from CARB and so makes the same assumptions about what's "worst". In other parts of the world, the CO2 and resource consumption are the biggest environmental impacts. Furthermore, there are plenty of clean, fuel-injected, catalyzed bikes around these days, plus still more than a few (mostly older) cars with ineffective or missing emissions controls. Despite all the above, if people with cars were better at car pooling, cars would win hands down - Just sayin!