The need for traffic information service systems that warn about traffic congestion and accidents through mobile devices, such as cellular phones, is increasing greatly now. To display clearly these informations for these services, a well-formed map is more useful than a detailed one in many cases. Although methods to generate well-formed map automatically are known as map summarization methods, summarization of road maps that cover wide areas has not been studied sufficiently. Therefore, we developed a new algorithm that summarizes the network structure of a detailed road network into a simple macroscopic structure. Further, we evaluated this algorithm?s effectiveness by experiments with 40 samples of road routes from the main road networks in Japan. The proposed method reduced the link number by 41.3% and reduced the fractal indices by 62.6%, and this proved simplification. And the proposed method improved the well-formed map by user evaluation. From these results obtained by our evaluation, we found that our method is effective for constructing a system for providing practical mobile traffic information services.