Your car is a big environmental nemesis, and Massachusetts is stepping in

Traffic on the Leonard P. Zakim Bunker Hill Memorial Bridge. –David L. Ryan/Globe Staff

Over the past decade, Massachusetts has made significant progress in reducing its carbon emissions, primarily by curbing pollution from power plants.

Now comes the hard part — limiting emissions from cars and other vehicles, which have surpassed power plants as the state’s largest source of greenhouse gases.

The Baker administration is considering sweeping measures that could transform the state’s transportation system, which is responsible for about 40 percent of emissions.