When travelling, the level of the road area and facility condition is different by region. In general, road ratio is the index to show how much the area of roads in the subject place and roughly measure the level of road service. The concept of road ratio can be differently defined by the purpose of the use, but it has been simply calculated by the ratio between the area and the road length of the administrative district. Therefore the capability of the road throughput and quality service elements were not fully considered, which is highly linked to the road rank, the number of lanes, and the accessibility to freeways. In order to tackle the limitation of the current road ratio index, this study developed the methodology for estimating road service index which consisted of two elements; 1) inner regional accessibility index and 2) inter regional accessibility index. The proposed methodology were greatly improved in that those indexes could capture the seamlessness and mobility of the road trips. With the proposed indexes, the subject area of the case study was the Chungcheongnam-do in South Korea. By doing so, the expert survey was conducted to the regional specialists for the Chungcheongnam-do who were taking charge of regional development, policies and public investment projects. As a result, there were the huge difference between the existing road ratio and the proposed index.For example, the cities with the high road ratio in Chungcheongnam-do show that the quality of the road service is relatively low because of high traffic volume. In other words, although the infrastructure is well constructed, the service index is sometimes underestimated. In the goodness of fitness, the congestion map is much more accuracy than the service index with the road ratio and is more understandable than the current methodology to describe the level of road service. Therefore, the proposed methodology is noteworthy in that both factors with the low penetration rate for the road infrastructure and the low service quality of the road throughput. In addition, the under-developedness index with this proposed index is most likely to assisting the reasonable judgement when applying to the Analytic Hierarchy Process.