The aim of this article is to provide a probabilistic economic model for investigating the ratio of investment for installing advertising boards (billboards) on rural roads. An economic model has been developed based on probabilistic incomes over a time period of five years. Data has been gathered using a designed questionnaire and analyzed based on normal distribution function in terms of profitability and incomes over time period of investment. The main innovation of the article which makes different from the other studies is to investigate the cost-benefit ratio based on the view of investor who needs to advertise its product. One of the rural roads on Yazd province in Iran, Named Mehriz-Yazd road, has been selected as case study and the results revealed that the proposed model can be used for all business companies who are dealing with their products' advertising investment.