Abstract: In order to provide theoretical basis for the traffic organization design of intersections，the whole delay characteristics of intersections under two kinds of left-turn traffic flow organizations，namely，the direct left-turn plan and the right-turn-straight-U-turn (Ｒ-S-U) plan，are analyzed in this paper． Based on the Webster delay model and the gap acceptance theory，the vehicle average delay models for the two kinds of traffic flow organizations and a discriminant model of the left-turn traffic flow organization are constructed by means of mathematical derivation． It is found that，with the whole intersection delay as the optimization objective，the R-S-U plan has more advantages when the left-turn traffic flow volume is smaller than a certain threshold; otherwise，the direct left-turn plan is more reasonable． The threshold of flow discriminant is related to the relationship between the left-turn traffic flow volume and the opposite direction traffic flow volume． Finally，the theoretical delay parameter of a typical intersection is calculated，and the simulation delay parameter is obtained through VISSIM． The results show that the theoretical calculation results are consistent with the simulation ones，which means that the constructed models are of higher accurate and reliable．

Key words: traffic engineering, left-turn traffic flow, right-turn-straight-U-turn, average delay at intersection, signal control, simulation