The duration of traffic signal lamp is determined by the traffic volume through the intersection, and different intersections’ duration are generally set different. The calculation process is complex. First, there must be data with expected traffic flow or current traffic flow and the form of entrance road arrangement obtained from traffic investigation. The so-called traffic flow is the number of vehicles going in all directions of each entrance road every hour. The setting of the entrance road refers to how many straight lanes, right turn lanes, straight right lanes and left turn lanes exist at an entrance. The following two concepts should be followed before calculation:
1. Saturation flow rate: under the given conditions, the saturation flow rate of a certain flow or several traffic flows passing through the intersection in saturated state in unit time is calculated by multiplying the basic saturation flow rate by a large number of correction factors.
2. Lane Group: the distribution of traffic flow among alternative entry lanes will gradually tend to a balanced state, which makes the traffic load level of each alternative entrance lane very close. Therefore, these alternative entry lanes form a lane combination, which is commonly referred to as lane group. Generally speaking, all the straight lanes and the right turn and left turn lanes constitute a lane group; The left turn lane and right turn lane form the lane group independently.