N.H. Rev. Stat. Ann. § 231:105

If 2 or more towns are chargeable with the expense of repairing and maintaining a highway they shall be liable for such damages and all costs and expenses of suits for the recovery thereof, in the proportion in which they are required to contribute towards its repair and maintenance; and the claimant may begin and prosecute proceedings for the recovery of such damages against all the towns jointly, or against the town in which the highway is situated.