The Rural Access Index (RAI), one of the UN Sustainable Development Goal indicators (SDG 9.1.1), represents the proportion of the rural population residing within 2 km of all-season roads. It reflects the accessibility of rural residents to transportation services and could provide guidance for the improvement of road infrastructure. The primary deficiencies in assessing the RAI include the limited studying area, its incomplete meaning and the absence of correlation analysis with other influencing factors. To address these issues, this study proposes the "Not-served Rural Population (NSRP)" as a complementary indicator to RAI. Utilizing multi-source open data, we analysed the spatial patterns of RAI and NSRP indicators for 203 countries and then explored the correlation between these 2 indicators and other 10 relevant factors. The main findings are as follows: 1) North America, Europe, and Oceania exhibit relatively high RAI values (>80%) and low NSRP values (<1 million). In contrast, African regions have relatively low RAI values (<40%) and high NSRP values (>5 million). There is a negative correlation between RAI and NSRP. 2) There is spatial autocorrelation and significant imbalances in the distribution of these two indicators. 3) The RAI exhibit a positive correlation with the factors showing levels of the development of countries such as GDP, education, indicating that improving the road infrastructure could reduce the poverty rates and enhance access to education. And in contrast with RAI, NSRP exhibit the completely negative correlations with these factors.

翻译：农村可达性指数（RAI）是联合国可持续发展目标指标（SDG 9.1.1）之一，表示居住在距离全年通行道路2公里范围内的农村人口比例。该指数反映了农村居民获取交通服务的便利程度，可为道路基础设施改善提供指导。当前RAI评估的主要不足包括：研究区域有限、内涵不完整，以及缺乏与其他影响因素的关联性分析。针对这些问题，本研究提出"未服务农村人口（NSRP）"作为RAI的补充指标。利用多源开放数据，我们分析了203个国家RAI与NSRP指标的空间格局，进而探究了这两个指标与其他10个相关因素的关联性。主要发现如下：1）北美、欧洲和大洋洲的RAI值相对较高（>80%），NSRP值较低（<100万）；而非洲地区的RAI值较低（<40%），NSRP值较高（>500万）。RAI与NSRP呈负相关关系。2）这两个指标的分布存在空间自相关性和显著不均衡性。3）RAI与GDP、教育等反映国家发展水平的因素呈正相关，表明改善道路基础设施可降低贫困率并提高教育可及性；与之相反，NSRP与这些因素呈现完全负相关关系。