Lane splitting of motorcycles has been proven to reduce urban congestion and emissions for society. A study by the Belgian consultancy Transport & Mobility Leuven found a 10% shift to two wheeled vehicles reduced traffic by 40%, and a 25% shift eliminated traffic altogether. California is currently the only state to allow lane splitting. Lane splitting is common in European and Asian countries, and has found to be effective and safe. Not only would lane splitting reduce congestion, but would also decrease gasoline consumption and emissions.
The study:
http://www.tmleuven.be/project/motorcyclesandcommuting/home.htm