Blocked Time of Permitted Left-Turn Lane Group with Two Opposing Lanes for Two Arrival Types

The blocked time is a portion of effective permitted left-turn green time blocked by opposing traffic until the left-turn vehicle can get an acceptable gap to complete a permitted left turn. In the Highway Capacity Manual, it is designated as the opposing approach queue clearance time, gq. The blocked time, denoted as gb, is a critical parameter in estimating delay for a signalized intersection because it affects not only left-turn saturation flow but also the shape of the delay area. This paper proposes a model for estimating blocked time for a left-turn lane group with two opposing lanes for well- and poorly coordinated signals. The proposed model was developed by directly considering the arrival types. Possible platoon arrival patterns during the green interval were categorized and then used to estimate the blocked time of the left-turn lane group. A comparison of the results from the proposed model and the existing models with CORSIM results indicated that the proposed model is more realistic in estimating the blocked time for left turns.