After any indebtedness is incurred under the provisions of this article, the treasurer of the county, during each year such indebtedness continues, shall set aside in a separate fund from the revenues received during such year from highway user taxes, including motor vehicle fuel taxes, and all other taxes, fees, charges or other monies returned to the county pursuant to Title 28, Chapter 18, Article 2 and section 42-6107, an amount sufficient to pay the interest and principal upon the installment on such indebtedness next maturing.