What requirements should the left turn signal lamps need to meet in road installation?

The independent left turn phase refers to giving the left turn traffic a separate phase around the control of the road traffic lights. In this phase, the left turn traffic is turn left turn traffic and stop the straight vehicles, thus reducing the hidden danger of left turn traffic flow delay and conflict with direct traffic. As the direct traffic flow is higher than the left turn traffic flow, setting a separate left turn phase may cause the overall delay increase of the intersection, so it is necessary to consider comprehensively in application. In general, we can refer to the following three aspects.


1. Below conditions should be considered and understood before installing the left turn phase.

a. If there is no left turn lane on the road, set a separate left turn lane first, and do not rush to set a left turn signal.

b. If a single left turn lane can not solve the traffic problem, then consider setting the left turn phase.

c. The influence of left turn phase in the process of coordinated signal control.

d. Collect traffic flow, speed, left turn delay and accident summary reports as much as possible.

e. Finally, refer to the following three conditions, and then consider whether to set the left turn phase.


If the following conditions of A, B and C can be met, it indicates that the setting of left turn phase may have certain value, but it does not mean that the setting of left turn phase is necessary. On the contrary, it should promote the further engineering evaluation of left turn phase.


Guideline A: Minimum peak hour traffic

1. Clause A refers to the left turn traffic flow in peak hours, which is the main condition for judging the adoption of left turn phase. This clause contains the generated values of left turn traffic flow and reverse through traffic flow, provides the interval between left turn requirements and reverse traffic flow, and other parts are functions of traffic flow.

2. Clause A is satisfied with one or both of the following situations:


a. The product of left turn traffic volume and one opposite through lane traffic flow is more than 50000 (VPH) ^ 2, and the product of left turn traffic volume and two opposite through lanes traffic flow is more than 9000 (VPH) ^ 2.


b. When the main road is 85% or the specified speed is 70km/h, the left turn traffic volume exceeds 80Vph; Or when 85% of the main road or the specified speed exceeds 70km/h, the left turning vehicles are delayed.


Guidance clause B: Left turn vehicle delay

1. This clause applies to delays mainly caused by left turn traffic.

2. When the delay of left turn vehicles is equal to or more than two vehicles per hour (any hour in an average working day), this clause shall be met.


Guidance clause C: Accidents

Because there are no left turn traffic lights, there are more than five accidents every year.

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