The main purpose of traffic signal phasing is to separate the conflicting or interfering traffic flows appropriately, and to reduce intersection traffic conflicts and interference. Traffic signal phase design is a key step in signal timing, determines the scientific and reasonable timing scheme, and directly affects the road intersection traffic safety and smooth flow.

First, the traffic signal related terms

1、Phase

In a signal cycle, a stream or several streams of traffic at any moment to get the exact same signal color display, then they get different colors (green, yellow, red) of the continuous complete signal phase called a signal phase. Each signal phase periodically alternates to get a green light display, that is, to get through the intersection of the “right of way”, “right of way” of each transition is called a signal phase phase, a signal cycle is composed of all the phases in accordance with the pre-set sum of the time periods. A signal cycle is composed of the sum of all the phase time periods set in advance.

2、Period

Cycle refers to a complete process of signal lamps displaying various light colors in turn.

3、Traffic flow conflict

When two different flows of traffic at the same time through a certain point in space, it will produce traffic conflict, and the point is called the conflict point.

4、Saturation

Lane corresponding to the actual traffic volume and capacity ratio.

Second, the phase design principles

1、Safety principle

Phase of the internal traffic conflict as little as possible, non-conflict traffic can be released in the same phase, the conflict of traffic should be placed in a different phase release.

2、Efficiency principle

Phase design should improve the utilization of time and space resources at the intersection. Too many phases will lead to an increase in lost time, thus reducing intersection capacity and traffic efficiency. Too few phases will reduce efficiency due to serious conflicts.

3, the principle of balance

Phase design needs to take into account the saturation balance between the various streams of traffic, should be based on the different streams of traffic reasonable allocation of the right of way. Should ensure that the phase between the internal flow of each direction of the flow ratio is not much difference, in order not to waste the green light time.

4, the principle of continuity

A flow in a cycle can get at least one consecutive green time; an import of all flows to be released in a continuous phase; if several streams of traffic share the lane, they must be synchronized release. For example, if straight and left-turn traffic share a lane, they must be released synchronously.

5、Pedestrian principle

In general, pedestrians should be released with the same direction of straight traffic, try to avoid the conflict between pedestrians and left-turning vehicles, for the longer crossing length (greater than or equal to 30 meters) of the intersection can be appropriate to implement the second crossing.