Northeast states could be close to an agreement on a regional program to control greenhouse gas emissions in the transportation sector, several people with knowledge of ongoing discussions told Bloomberg Environment.

A statement from the states could come by the end of December, although the details remain unclear. Connecticut, Delaware, Maryland, Massachusetts, New York, Rhode Island, Vermont, and Washington, D.C., agreed to develop the plan.

Ben Grumbles, secretary of Maryland’s Department of the Environment, said Dec. 4 that an announcement from the states on addressing greenhouse gases from transportation was expected “in the coming weeks.”

Massachusetts and New...