First class national highways which cross urban city were always designed as municipal roads as well. In this case, the enhancement of these highways should consider more influence factors than traditional cases, i.e. the satisfied performance of high-level pavement; the functional properties for urban roads. As a consequence, items such as land-using, planning, environmental protecting, sighting designing, safety ensuring and cost analyzing should be all evaluated. The type of medial dividers should be chosen based on actual condition for these roads. In this study, four kinds of common-used medial dividers were introduced, including green median strip, concrete barrier, steel guard fence and steel guard fence with flower bed. For designing reasonable medial divider of urban street, the social requirement on specific location should be considered as well as technical feasibilities.%某路段的国道为一级公路兼做城市主干道的道路，在此类道路的改造升级过程中既要保留高等级公路的性质，又要充分考虑市政道路的功能，同时需要综合考虑用地、规划、环保、景观、安全性以及造价等多种因素。此类道路的中央分隔带方案的选定应根据具体情况按照实际需要予以选择。文中叙述了常见的四类中央分隔带形式，分别为绿化分隔带形式、混凝土护栏形式、钢护栏形式、钢护栏+花坛形式。在城市道路的建设过程中可以按照项目所在地的社会需求，结合工程技术要求，确定合理的中分带（护栏）类型。
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