Green light interval
Basic definition
The green light interval is the end time of a conflicting green light of one traffic flow and the start of a green light of the next traffic flow. The time interval between moments [1] (see page 15). The different areas passed by the two streams are called conflict areas, and the most dangerous point is called the key conflict point. The minimum green light interval that can ensure traffic safety is called the shortest green light interval. As shown in Figure 1.
Figure 1? Conflict areas and key conflict points between conflicting traffic flows,
Schematic diagram of clearing distance s clearing i and entering distance s advancing j
Contents< /p>
Basic definition
Purpose of setting
Origin?
A country without traffic lights? ?
Why are traffic lights red, yellow and green?
Setting purpose and related terms
At intersections controlled by signal lights, conflicts can only be separated by traffic signals, allowing different traffic units to take turns passing in the order of traffic signals. Provide a safe and uninterrupted passage for permitted traffic flow.
For different traffic flows i and j with traffic conflicts, traffic units take turns entering the conflict area in the order of traffic signals. The movement of the traffic tail unit released after the green light i ends from its stop line to crossing the key conflict point is To clear, the length of its motion trace is the clearing distance si, and the time it takes is the clearing time ti; the movement of the first traffic unit that starts to release at green light j from its stop line to the key conflict point is entry, and the length of its motion trace is the entry distance sj , the time it takes is the entry time tj. It can be seen from Figure 1 that the difference between reaching and crossing the key conflict point is not only the length of the entire conflict area, but also the length of a clearing unit.
Calculation of the traditional shortest green light interval
A calculation formula for the shortest green light interval Imij is contained in [1] (see page 15). For example, formula (1):
Imij=pass time + ti–tj?(1)
In the formula: Imij: from the end of green light i to the start of conflicting green light j The shortest green light interval required to light up, (s);
ti: is the clearing time for the tail unit of green light i from the stop line to crossing the key conflict point, (s);
< p>tj: is the entry time for the first unit of green light j to reach the key conflict point from the stop line, (s);Passage time: the time interval between the end of the green light time and the beginning of the clearing time [1 ] (page 16), (s).
[1] lists 6 examples of the "passing time" of 6 different traffic flows: 3, 2, 3, 0, 1, 0s, all of which are less than or equal to yellow light time A, which is unsafe. (1) is the best description of the calculation principle of Imij in traditional literature, but its Imij is too small and loses safety and efficiency. Of course, if Imij is too large, it will inevitably lose traffic efficiency, and it will also be complained and reviled by people. The optimal solution is most likely to occur on the constraint boundary. Therefore, it is very important to accurately calculate Imij. Many documents do not calculate or cannot calculate Imij at all, and it is even more wrong to directly design Iij.
Improvements in the calculation of the shortest green light interval
In order to ensure safety, based on the concept of "prudent specification", as the lower limit, Imij should consider the maximum value among various possible demand values, and should Consider the difference between a slow train and a fast train. That is:
Imij=Max{passing time+ti–tj}=A+Max{ti}–Min{tj}(2)
In the formula: A: yellow light time , (s);
Max{ti}: usually the 85% bit value of the cumulative frequency distribution function of ti[2], corresponding to the slowest clearing traffic flow, (s);
Min{tj}: Usually the 15% bit value of the cumulative frequency distribution function of tj, corresponding to the fastest entering traffic flow, (s).
Compared with formula (1), the larger Imij value of formula (2) can ensure safety, reduce accidents, congestion and blockage at signalized intersections, and is more likely to lead to an overall reduction of literature [3 ] said the intersection control system collapsed. The United Nations' Global Plan for the Decade of Action on Road Safety 2011-2020 states that currently "road traffic system designers, not road users, should be primarily responsible for accidents, congestion and congestion at signalized intersections" [4]. Therefore (1) should be abolished and (2) should be promoted.
The method of designing a control scheme using formula (2) has applied for international patent PCT/CN2011/070879.
References
[1] Traffic Signal Control Guidelines - Current German Specifications (RiLSA), Edition 1992, [Germany] Road and Traffic Engineering Research Society, edited by Li Keping Translated, Beijing: China Construction Industry Press, May 2006.
[2] Yu Quan, ed., Basics of Urban Traffic Signal Control [M], Beijing: Metallurgical Industry Press, 2011.1.
[3]National?Cooperative?Highway?Research?Program:?Guidance?for?Implementation?of?the?AASHTO?Strategic?Highway?Safety?Plan?Volume?12:?A?Guide? for?Reducing?Collisions?at?Signalized?Intersections, NCHRP?RANSPORTATION?RESEARCH?BOARD?EXECUTIVE?COMMITTEE?2004?(Membership?as?of?January?2004),?Project?G17-18(3)?FY' 00,?ISSN?0077-5614,?ISBN?0-309-08760-0
[4]?United Nations Global Plan for the Decade of Action for Road Safety 2011-2020, adopted by the United Nations General Assembly in March 2010 Resolution A/RES/64/255/view/5977857fa26925c52cc5bfcf.html?from=rec&pos=0&weight=4&lastweight=2&count=5