Two or more municipalities, by vote of their respective boards of aldermen and selectmen, may unite for the purpose of improving or repairing any portion of a highway passing into or through each of them. When a union has been effected, the officials of the respective municipalities shall constitute a joint committee which shall be the agent of the several municipalities and may appoint one person to supervise the actual work. (Added 1985, No. 269 (Adj. Sess.), § 1.)