Abstract: The articulated train is a very important transportation tool for special equipment in China’s infrastruc- ture construction． It has high requirements for the passability and safety of road design． However，the current specification doesn’t fully consider the safe traffic demand of articulated trains． The design standard of such spe- cial roads needs to be improved． According to the principle of rear wheel steering of the articulated train，and con- sidering the vehicle size and the horizontal curve index，the wheel trajectory was analyzed and the road widening value model was improved． It proposed a method of selecting circular curve radius limited by the road widening value when the filling and excavating conditions are limited． Taking the road widening less than 3 meters as an ex- ample，the method suggested the recommended values of the turning radius of the two types of vehicles “steering rear wheel”and “non-steering rear wheel”under different wheelbase and corner conditions are 20 ～80m． In or- der to ensure the safety of the vehicle in the process of turning and the inside and outside of the road，two safety design indexes，namely “lateral clear distance”and “over-length permissible value”were proposed to analyze the demand and difference types of vehicles． The research results will provide engineers with accurate design refer- ences，reduce the cost of road reconstruction and expansion，and improve the transportation safety of large car- goes．

Key words: articulated train, road widening value, lateral clear distance, over-length permissible value