BOSTON — Though only Massachusetts and three of the 13 state and city governments that had been part of discussions around creating a regional effort to staunch vehicle emissions along the East Coast agreed Monday to be part of the program from the get-go, Gov. Charlie Baker said it is "a pretty good place to start." Twelve states and Washington, D.C. began the process more than two years ago of developing a regional "cap-and-invest" program to reduce carbon pollution from cars and trucks and generate the resources needed to expand clean transit options and improve public health. On Monday, the leaders of four jurisdictions -- Massachusetts, Rhode Island, Connecticut and Washington, D.C. -- signed on to be the program's initial members.