Technical parameters of green light interval

1, the calculation of the traditional shortest green light interval time

[1] gives the calculation formula of the shortest green light interval Imij (see page 15). Such as (1):

Imij= transmission time+ti–TJ (1)

Where: Imij: the shortest green light interval time to be set from the end of green light I to the beginning of conflicting green light J, (s);

Ti: the emptying time of the tail unit of green light I from the stop line to crossing the critical conflict point, (s);

Tj: the entry time of the first unit of the green light J from the stop line to the critical conflict point, (s);

Transit time: the time interval from the end of green light time to the beginning of sorting time (16 page),

(United States)

[1] Six examples The "transit time" of six different traffic flows is less than or equal to the yellow light time a, which is unsafe. Directory 1 is the best description of the calculation principle of Imij in traditional literature, but its Imij is too small to be safe and efficient.

Of course, if Imij is too large, it will inevitably lose traffic efficiency, and it will also be complained and reviled.

2. The yellow light time is the maximum transit time.

The yellow light is located between the end of the green light and the beginning of the red light, and has a certain length of time, which is called yellow light time or yellow light time. The purpose is to give a warning and a buffer: "The red light that is forbidden to pass is about to light up. Don't run a red light by mistake. " So that legal vehicles that do not exceed the maximum speed limit can park safely in front of the stop line in front of the red light; It is also necessary to enable those vehicles that cannot stop safely near the stop line to cross the stop line safely at normal speed before the red light. Objectively speaking, the distance that can't be safely parked is greater than the minimum safe distance between driving on the expressway and the car in front of the same lane stipulated in the Road Crossing Law. Because the front car is different from the fixed stop line, the front Xiangqian Che still has a braking distance. It can be said that the yellow light is a green light and more of a warning. When the yellow light is on, vehicles can safely pass through the parking line at normal speed. According to the stop line method, all vehicles crossing the stop line can continue to move forward and pass the intersection before the red light signal appears. So crossing the stop line means crossing the intersection, and the yellow light is not responsible for clearing the intersection. The task of clearing the road surface of the intersection can only start from the end of the yellow light, and the length of the yellow light has nothing to do with the size and width of the intersection.

3. Why do many people think that "running yellow lights" will pose a threat to traffic safety at intersections?

It may be influenced by the wrong viewpoint and behavior of "compulsory emptying task at yellow light intersection" in literature [2]-[6]. Many people think that "running yellow lights" will pose a threat to traffic safety at intersections.

If so, why? The general answer is "because the vehicles in the conflicting direction have entered the intersection".

If we continue to ask responsibly: Why do vehicles in the conflicting direction enter the intersection so early?

By asking this question, the answer to the real threat to traffic safety is obvious.

What really threatens the safety of intersections is not the behavior of "running yellow lights", but the signal light of "letting vehicles in the conflicting direction enter the intersection so early". The setting of green light interval is unreasonable, not greater than or equal to the shortest green light interval, or the shortest green light interval is designed too short.

4. China people's safety improved the calculation method of the shortest green interval.

The optimal scheme is most likely to appear on the constrained boundary. Therefore, it is very important to calculate Imij accurately. However, in many literatures, it is even more wrong to design Iij directly without calculating or calculating Imij.

In order to ensure safety, based on the concept of "prudent supervision", Imij is taken as the lower limit, and the maximum of various possible demand values and the difference between local trains and express trains should be considered. That is, the safety improvement of the calculation method of the shortest green light interval is as follows:

imij = Max { transit time+ti–TJ } = a+Max { ti }–min { TJ }(2)

Where: a: yellow light time, (seconds);

Max{ti}: usually 85% of the cumulative percentage distribution function of ti, corresponding to the slowest traffic flow, (s);

Min{tj}: it is usually 15% of the cumulative percentage distribution function of tj, corresponding to the fastest incoming traffic flow, (s).

Compared with formula (1), formula (2) has a larger Imij value, which can ensure safety, reduce accidents, congestion and congestion at signalized intersections, and is more likely to lead to the overall reduction of intersection control system collapse mentioned in reference [8]. The United Nations Global Plan for the Decade of Action for Road Safety (20 1 1-2020) points out that road traffic system designers, not road users, should be mainly responsible for accidents, congestion and congestion at signalized intersections at that time. Therefore, (1) should be abolished and (2) should be popularized.

The method of designing control scheme by using formula (2) has applied for international patent PCT/CN2011/070879.

5. Possible range of shortest green light interval.

A large number of calculations show that the shortest green light interval at actual intersections may be between -8 ~ 15. According to Formula (2), the shortest green light interval depends on the emptying distance and entering distance of road channelization, and the sequence of conflicting traffic flows.

6. Is the green light interval less than 0 safe?

The "shortest green light interval" itself is a constraint transformation of release time, which transforms the basic constraint of "ensuring traffic safety and avoiding traffic conflicts at key conflict points" into the basic constraint of "the time for conflicting traffic flows to cross their respective stop lines". As long as it meets the requirements, it will ensure safety. In fact, on page 87, line 2-5 of [1], it is discussed that "deliberately displaying or switching to the green light signal of conflicting traffic flow at the same time will not cause harm to traffic under special circumstances (such as short or negative green light interval)."

7. Expression of green light interval and "all red" signal.

Because the green light interval can be less than 0, there is no expression of green light interval, and there is no "yellow light+full red" as mentioned in some documents. The reason is: 1, the duration of the yellow light is determined by the entrance speed of a traffic flow and other factors, see the entry "the duration of the yellow light". 2. The green light interval is determined by the sequence of two traffic flows, clearance distance, entry distance, speed and other factors. 3. All-red traffic will be banned, because you don't know the road conditions and should be cleared only when the signal light is on. These three "wind, horse and cow" are irrelevant and cannot replace each other. For example, the green light interval between east straight and west left only involves east straight and west left, and has nothing to do with the green light interval between west straight and east left traffic. Just because the green light interval between the east straight line and the west left line is longer than the yellow light duration, the normal release time of the west straight line or the east left line traffic cannot be limited.