Abstract: Heavy vehicles account for a large proportion on ordinary highways. In order to solve the occlusion problem that heavy vehicles shelter roadside traffic signs, an analysis was made for the sign recognition process of car drivers at the median lane being occluded by heavy vehicles at the outside lane on an ordinary bidirectional highway with 2 lanes in each direction, and the calculation formulas for occlusion length and occlusion probability in the sign recognition process was derived. Then, the calculation flow to determine the duplicate setting times of roadside traffic signs was designed, and a model for calculating the space between the duplicated traffic signs was established. The proposed method was verified by an example. The results show that, when the speed limit sign is duplicated once, the probability that the two speed limit signs are both occluded by heavy vehicles is 0.023, and the best space between duplicated traffic signs is 155 m.