Why Cutting Car and Truck Emissions Is So Hard

State lawmakers and regulators are turning their eyes to the road in the fight against climate change, recognizing that the transportation sector now produces more greenhouse gas emissions than any other portion of the economy.

They are finding few simple solutions.

The Transportation and Climate Initiative released a proposal last month to limit the amount of carbon that fuel suppliers are allowed to emit. The group is made up of 12 Eastern and Mid-Atlantic states plus the District of Columbia, many of which are part of a similar joint effort that has curbed power-sector emissions in the region.

The transportation proposal — which will require states to opt in before it takes effect — is off to a much rockier start, with at least one governor already denouncing it.