N.H. Rev. Stat. Ann. § 228:26

If the moneys in the highway fund are not sufficient to provide the funds authorized by RSA 228:25, the treasurer is authorized to borrow on the state's credit at the lowest rate of interest obtainable, such sums as may be necessary to provide said funds; provided, that at no time shall the indebtedness of the state pursuant to this section exceed $1,000,000; and provided further, that such indebtedness shall be repaid from revenues within 3 years.