Traffic signal lamp is based on the length of the traffic through the intersection to determine the traffic, different intersections are generally different. The calculation process is more complex. First of all, there must be some data is expected to traffic flow or traffic investigation of the existing traffic flow and import road set form, etc.. The so-called traffic flow is each hour each entrance to all directions to the number of vehicles imported setting is an imported have how many straight lane, right turn lane, straight right lanes and left turn lanes. Two concepts are introduced in the calculation.

1 saturation flow rate

Saturation flow rate: under given conditions, a certain unit of traffic flow or a few units of traffic flow per unit of time to saturation state through the intersection of the flow value (car / hour).

The saturation flow rate is calculated by multiplying a lot of correction factor with the base saturation flow rate.

2 Lane Group

The distribution of traffic flow in the alternative entrance lanes will gradually tend to be a state of equilibrium, so that the traffic load level of the imported lanes is very close. As a result, these alternative import lanes constitute a form of a combination of lanes, known as the habit of lane group.

Generally speaking, all of the straight lane and go straight, turn right, go straight turn left carpool lane constitute a lane group; and left lanes, right turn lane separate lane formation group.

Generally different intersection, signal cycle and green time is different. But there are special circumstances, such as coordinated control (Lv Bo), the two crossing distance too close, etc..

According to the control mode, the intersection signal control can be divided into timing control, inductive control and adaptive control.

General city (Nanjing City, for example) signal lights in different time periods and the green light is not the same, because the traffic flow in different times have different characteristics.

In China there is no national signal control specification (referring to the timing of the design), and some places have the relevant norms. Most parts of the country with fixed 3 seconds, yellow light, 1s Quanhong (if needed), and in these two time abroad also need to according to the speed limit and geometrical condition to configure.