Route 126 past Walden Pond in Concord/Lincoln is paved... from the Lincoln line almost to Baker Bridge Road. If you have been avoiding that stretch, as I have, they only have the topcoat to put on and it will be smooth sailing.

Also, if you are headed through Carlisle, these roads have been improved this summer:
River Road (aka Monument Street on Concord end)
West Street
Rutland Street

Enjoy!