This paper investigated the influences of ramp traffic flow on the lane utilization for signalized intersection approaches which are adjacent to an off-ramp-street junction. The statistical test showed a correlation between lane utilization and the ramp traffic flow. As the ramp traffic flow increases, the left lanes are less utilized and the right lanes are more utilized. The lane utilization factors are calculated by applying traffic data collected from the Seoul Metropolitan area. The utilization factors are 1.113 for 2 lanes, 1.124 for 3 lanes, and 1.131 for 4 lanes. The lane utilization factors proposed in the paper show higher values than those in current Korea Highway Capacity Manual (KHCM) under the conditions that the number of lanes is 2 or 3. However, the lane utilization factor for 4 lanes in the paper shows lower value than in KHCM. The ramp traffic flow causes more utilization of the right lanes than at normal signalized intersections and the extent gets larger as the number of lanes decreases. Based on the results of the paper, the lane utilization factors at signalized intersection approaches should be revised and reasonable capacity should be recalculated if the signalized intersection is adjacent to an off-ramp-street junction.

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