CN109598949B

CN109598949B - T-shaped intersection emergency vehicle preemption control method based on timed Petri network

Info

Publication number: CN109598949B
Application number: CN201811441452.8A
Authority: CN
Inventors: 黄波; 赵志霞; 赵凌波; 裴焱栋; 蔡志成
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2018-11-29
Filing date: 2018-11-29
Publication date: 2021-06-22
Anticipated expiration: 2038-11-29
Also published as: CN109598949A

Abstract

The invention discloses a T-shaped intersection emergency vehicle preemption control method based on a timed Petri network, which comprises the following steps: firstly, setting the maximum capacity values of all libraries in the Petri network; then, according to the state of the traffic lights when the emergency vehicles arrive at the T-shaped intersection, different emergency scenes are divided; then establishing Petri network models corresponding to different emergency scenes by using the timed Petri network; and finally, combining the Petri network models corresponding to different emergency scenes to construct a T-shaped intersection emergency vehicle preemption control system, wherein the system realizes T-shaped intersection emergency vehicle preemption control. The method can effectively avoid the situation that the emergency vehicles conflict at the T-shaped intersection, improve the traffic efficiency of the intersection and effectively shorten the time required by the emergency vehicles to reach the destination.

Description

T-shaped intersection emergency vehicle preemption control method based on timed Petri network

Technical Field

The invention belongs to the technical field of traffic safety control, and particularly relates to a T-shaped intersection emergency vehicle preemption control method based on a timed Petri network.

Background

Emergency Vehicle Preemption (EVP) systems are intended to provide an emergency vehicle with a green light to indicate its entry into an intersection while providing a red light to others. There are many EVP technologies in use today, including optical, infrared, acoustic, and radio-based transmitter/detector systems. In addition, An ITS middleware is proposed in the article 'BEVOR: An NTCIP-based interactive frame for emergency vehicle preemption and STMF' for National Traffic Communication (NTCIP) based on ITS protocol. By using the NTCIP protocol at the communication layer, interoperability of communication and data can be achieved between most devices and devices. A mechanism is proposed in the article "a centralized traffic control mechanism for evaluating and using the DSRC protocol", in which a central server is used to monitor and control all traffic information to support real-time traffic information and services of emergency vehicles and to calculate the shortest path that an emergency vehicle passes through. An algorithm for traffic light preemption in a vehicle network using the spatial and angular information of the vehicle contained in the coordination awareness message transmitted by the algorithm is proposed in the article "a Novel CAM based traffic light prediction for efficacy reasons". Although there are many methods based on different types of traffic control strategies, these methods mainly solve EVP problems such as security and transportation efficiency based on advanced communication, information and electronic technologies, and information required for wireless communication means is not easily collected under actual traffic conditions, especially severe weather conditions, which increase environmental interference.

A Traffic Safety Control system for Emergency Vehicle Preemption at intersections by Using a timing Petri network is provided in the article Design of Traffic Safety Control Systems for Emergency Vehicle Preemption. Their research is directed to solving the pressing situation where an emergency vehicle at an intersection collides with another vehicle. Once an emergency vehicle is detected entering the intersection, the traffic conditions of the vehicles in the same direction as the emergency vehicle can be controlled by changing their traffic lights. The system is based on a two-phase control system to control the crossroad and cannot be applied to other forms of traffic crossroads. When the traffic flow at the intersection is too large, the left-turning vehicles conflict with each other, so that the passing efficiency of the whole intersection is influenced, at the moment, the two-phase control system cannot effectively coordinate the work of the intersection, and cannot effectively coordinate the conflict between the straight-going vehicles and the left-turning vehicles. In addition, in practical situations, traffic intersections comprise many types, for example, T-shaped intersections are also quite common in cities, and the existing control methods cannot effectively control the T-shaped intersections.

Disclosure of Invention

The invention aims to provide a method which can solve the control problem of emergency vehicle preemption at a T-shaped intersection and further improve the traffic efficiency of the T-shaped intersection.

The technical solution for realizing the purpose of the invention is as follows: a T-shaped intersection emergency vehicle preemption control method based on a timed Petri network comprises the following steps:

step 1, setting the maximum capacity values of all libraries in a Petri network;

step 2, dividing different emergency scenes according to the states of traffic lights when the emergency vehicles reach the T-shaped intersection;

step 3, modeling an emergency vehicle preemption control system at the T-shaped intersection by utilizing a timed Petri network aiming at different emergency scenes to form Petri network models corresponding to different emergency scenes;

and 4, combining the Petri network models corresponding to different emergency scenes to construct a T-shaped intersection emergency vehicle preemption control system, wherein the system realizes T-shaped intersection emergency vehicle preemption control.

Compared with the prior art, the invention has the following remarkable advantages: 1) the invention adopts a three-phase control method to realize the control of traffic lights at specific phases of the intersection, effectively reduces the conflict between the straight vehicles and the left-turning vehicles at the intersection, and can effectively solve the problem that the conflict occurs in the traditional two-phase traffic control without considering the advancing direction of the emergency vehicle; 2) the traffic light control of the T-shaped traffic intersection is realized by adopting a simpler control method by setting the maximum capacity value of the database; 3) the invention models the emergency vehicle control system of the T-shaped intersection, overcomes the defect that the prior art can only be applied to the intersection, effectively avoids the condition that the emergency vehicles conflict at the T-shaped intersection, improves the traffic efficiency of the intersection and effectively shortens the time required by the emergency vehicles to reach the destination.

Drawings

Fig. 1 is a flowchart of a T-junction emergency vehicle preemption control method based on a timed Petri network.

FIG. 2(a) shows an emergency scenario (R) in an embodiment of the present invention_sw，G_we，R_es) And (b) is a reachable graph corresponding to the emergency scene.

FIG. 3(a) shows an emergency scenario (R) in an embodiment of the present invention_sw，R_we，G_es) And (b) is a reachable graph corresponding to the emergency scene.

FIG. 4(a) shows an emergency scenario (Y) in an embodiment of the present invention_sw，R_we，R_es) And (b) is a reachable graph corresponding to the emergency scene.

FIG. 5(a) shows an emergency scenario (R) in an embodiment of the present invention_sw，R_we，R_es) And (b) is a reachable graph corresponding to the emergency scene.

FIG. 6(a) shows an emergency scenario (R) in an embodiment of the present invention_sw，R_es，R_we) And (b) is a reachable graph corresponding to the emergency scene。

FIG. 7(a) shows an emergency scenario (R) in an embodiment of the present invention_sw，R_we，R_es) And (b) is a reachable graph corresponding to the emergency scene.

FIG. 8(a) shows an emergency scenario (R) in an embodiment of the present invention_sw，R_we，Y_es) And (b) is a reachable graph corresponding to the emergency scene.

FIG. 9(a) shows an emergency scenario (R) in an embodiment of the present invention_sw，Y_we，R_es) And (b) is a reachable graph corresponding to the emergency scene.

FIG. 10(a) shows an emergency situation (G) in the embodiment of the present invention_sw，R_we，R_es) And (b) is a reachable graph corresponding to the emergency scene.

Fig. 11 is a system for preempting emergency vehicles at a T-junction according to an embodiment of the present invention.

Fig. 12 is a reachable diagram of the system of fig. 11.

Detailed Description

With reference to fig. 1, the method for preempting and controlling emergency vehicles at T-shaped intersections based on the timed Petri network includes the following steps:

step 1, setting the maximum capacity value of all libraries in the Petri network. Preferably, the maximum capacity value of the library is set to 1.

Step 2, according to the state of the traffic lights when the emergency vehicles arrive at the T-shaped intersection, dividing different emergency scenes, specifically:

suppose the intersection at one end of the T-shaped transverse direction is S₁The other end of the road junction is S₂The T-shaped crossing in the vertical direction is S₃，S_ijRepresenting a certain phase, S, in three-phase traffic control_ijG represents S_ijPhase is in green state, S_ijY represents S_ijPhase is in yellow light state, S_ijR represents S_ijThe phases are in a red light state, where i and j are 1, 2, and 3, and the different emergency scenes are:

(1) the instant emergency scene, i.e. the case where the advancing direction of the emergency vehicle is perpendicular to the traffic flow, includes the following 5: (S)₃₁R，S₁₂G，S₂₃R)，(S₃₁R，S₂₃G，S₁₂R)，(S₃₁Y，S₁₂R，S₂₃R)，(S₃₁R，S₁₂R，S₂₃R) and (S)₃₁R，S₂₃R，S₁₂R); wherein (S)₃₁R，S₁₂R，S₂₃R) is S₁₂R will change to green state, (S)₃₁R，S₂₃R，S₁₂R) is S₂₃R will change to a green state;

(2) indirect emergency scenes, i.e., situations in which the direction of advance of the emergency vehicle is parallel to the traffic flow, include the following 4: (S)₃₁R，S₁₂R，S₂₃R)，(S₃₁R，S₁₂R，S₂₃Y)，(S₃₁R，S₁₂Y，S₂₃R) and (S)₃₁G，S₁₂R，S₂₃R)。

And 3, modeling the emergency vehicle preemption control system at the T-shaped intersection by utilizing the timed Petri network aiming at different emergency scenes to form Petri network models corresponding to different emergency scenes.

Wherein, in modeling:

the change of the traffic lights at the T-shaped intersection is represented by the change of the number of the tokenks in the Petri network library, and the change is specifically as follows: when the traffic light control system works normally, no emergency vehicle enters the T-shaped intersection, and when the department of the traffic light is available, the traffic light is in a working state, namely, a red or yellow or green light is on; when there is no token in the library, the lamp is not on;

representing a temporal rule using transitions of a Petri net, different transitions representing different temporal rules, the temporal rules comprising: triggering transition instantly, the transmission of which does not need time delay; a timed triggered transition, whose transmission requires a fixed delay; an exponential distribution triggering transition, the transmission of which requires an exponential distribution delay;

the method for expressing the rule in the traffic light control system by using the relation arc between the Petri network middle place and the transition specifically comprises the following steps: in the three-phase control of the T-shaped intersection, if a green light of one traffic light is in a working state, red lights of all other traffic lights are in a working state.

Modeling an emergency vehicle preemption control system at a T-shaped intersection by utilizing a timed Petri network to form Petri network models corresponding to different emergency scenes, and specifically comprising the following steps:

step 3-1, initializing the distribution of the tokans in the Petri network library: the number of the Token in the bank corresponding to the red light in the three-phase traffic light at the T-shaped intersection is 1, and the number of the Token in other banks is 0;

step 3-2, setting a fixed time interval for triggering the Petri network transition, specifically: the red light duration of each intersection lamp of the T-shaped intersection is T₁Green light duration of t₂Duration of yellow light is t₃(ii) a Wherein t is₁、t₂、t₃The value of the traffic flow is freely determined according to the actual traffic conditions of different T-shaped intersections, namely the traffic flow;

3-3, establishing a Petri network model for controlling traffic lights at the T-shaped intersection by using the timed Petri network; the method specifically comprises the following steps:

forming a petri net model by the intersection lamps of the three-phase traffic lamps according to the change sequence of red, yellow and green to realize the mutual exclusion change of each intersection lamp, wherein the three phases are respectively expressed as S₃₁、S₁₂、S₂₃The method specifically comprises the following steps:

step 3-3-1 with S₃₁For example, a depot P that will represent a red light₁As an input depot including red light duration transitions, the depot P representing a green light₂As the output library containing red light duration transitions; further store P₂As an input depot including green duration transitions, a depot P representing yellow lamps₃As the output depot comprising green light duration transitions; further store P₃As an input depot including yellow light duration transitions₁As the output library containing the yellow light duration transition;

step 3-3-2, adding a control library among the three-phase traffic lights, specifically: adding control stores P₂₁As S₃₁The phase traffic light control structure comprises an output library for green light duration transition, and P is converted into₂₁As S₁₂Phase traffic light control structureAn input library including red light duration transitions; in phase S₁₂And phase S₂₃Adds a control depot P in between₂₂(ii) a Adding control stores P₁₁As S₃₁The phase traffic light structurally comprises an output bank of red light duration transitions, and P is₁₁As S₁₂The phase traffic light control structure comprises an input library of green light duration transition; in phase S₃₁And phase S₂₃Phase S₁₂And phase S₂₃Respectively add control stores P in between₁₂And P₁₃。

And 3-4, establishing Petri network models corresponding to different emergency scenes on the basis of the models established in the step 3-3. The method specifically comprises the following steps:

the parameters are set as follows: immediate trigger transition T_iOutput library of (1) is P_s(ii) a Exponential distribution triggered transition to T_sBy triggering T_sChanging the state of each cross-channel lamp; from depot P_qConnecting the Petri network models of the control systems corresponding to the different emergency scenes with the model established in the step 3-3; transition T_eThe traffic light control system is used for realizing the recovery of the traffic light control system to a normal working state after the emergency vehicle leaves the T-shaped intersection; depot P_mThe number of emergency vehicles for effectively controlling the entrance to the T-shaped intersection is 1;

instant trigger transition T in Petri network model for indicating traffic light control of T-shaped intersection when emergency vehicle arrives at T-shaped intersection_iIs triggered, T_iOutput depot P_sAdding 1 to the Token number in (1); with P_sTriggering transition T as an exponential distribution_sBy triggering a transition T when an emergency vehicle enters a T-junction_sTo avoid emergency situation of the system, this time the depot P_qThe system comprises a Token which can prevent the traffic light from changing before the emergency vehicle leaves the system;

in emergency scene (S)₃₁R，S₂₃G，S₁₂R) case is as an example: depot S₃₁R，S₂₃G，S₁₂R，P₁₂And P₁₃The Token number in (1) assumes the arrival direction of the emergency vehicleIs S₃₁At this time, an emergency occurs, and the exponential distribution triggers transition T_sWith S₂₃G，P₁₂And P₁₃As its input library, S₂₃Y、P_mAnd P_qAs its output depot, by triggering a transition T_sThe occurrence of an emergency scene is effectively avoided; depot P_qAs S₃₁The phase includes an output library of green duration transitions, and is used as S₂₃Input post including red light duration transitions on phase, post P_qAnd P_mAs transition T_eBy triggering a transition T when an emergency vehicle leaves a T-junction_eRestoring the traffic light to an initial normal operating state, thereby establishing an emergency scene (S)₃₁R，S₂₃G，S₁₂R) corresponding Petri net model; and (3) establishing a Petri network model corresponding to all the emergency scenes in the step 2 in the same way.

And 4, combining the Petri network models corresponding to different emergency scenes to construct a T-shaped intersection emergency vehicle preemption control system, wherein the system realizes T-shaped intersection emergency vehicle preemption control. The method specifically comprises the following steps: and integrating arcs from all libraries to the transition or arcs from the libraries to the transition in the Petri network model corresponding to all emergency scenes into a complete control chart, thereby constructing a T-shaped intersection emergency vehicle preemption control system, and realizing T-shaped intersection emergency vehicle preemption control by the system.

The present invention will be described in further detail with reference to examples.

Examples

step 1, setting the maximum capacity values K (p) of all libraries in the Petri network to be 1, and ensuring that the libraries have control functions.

And 2, dividing different emergency scenes including 9 emergency scenes into an instant emergency scene and an indirect emergency scene according to the state of the traffic light when the emergency vehicle reaches the T-shaped intersection, wherein:

A. instant emergency scenes, including the following 5:(R_sw，G_we，R_es)，(R_sw，R_we，G_es)，(Y_sw，R_we，R_es)，(R_sw，R_we，R_es) And (R)_sw，R_es，R_we) (ii) a Wherein (R)_sw，R_we，R_es) When R is_weWill turn into green light, (R)_sw，R_es，R_we) When R is_esWill turn into a green light.

B. Indirect emergency scenarios, including the following 4: (R)_sw，R_we，R_es)，(R_sw，R_we，Y_es)，(R_sw，Y_we，R_es) And (G)_sw，R_we，R_es)。

Step 3, modeling the emergency vehicle preemption control system of the T-shaped intersection by utilizing a timed Petri network according to the 9 emergency scenes in the step 2 to form Petri network models corresponding to different emergency scenes, and specifically comprising the following steps:

step 3-1, initializing the distribution of the tokens in the repository, i.e. the repository p in the initial state₃,p₆,p₉The number of the Tokens on the library is 1, and the number of the Tokens in other libraries is 0;

step 3-2, the traffic lights at the crossroad change according to a fixed time interval, i.e. t₁,t₄,t₇Has a value of 5, t₂,t₅,t₈Has a value of 60, t₃,t₆,t₉A value of 3; triggering the transition according to a triggering rule of the transition;

3-3, establishing a petri net model for controlling the traffic light of the intersection according to the specific intersection condition, specifically: each phase of the three-phase traffic light forms a petri net structure according to the change sequence of red, yellow and green, so as to realize mutual exclusion change of the red, yellow and green traffic light on a specific phase, which also accords with the change rule of the real traffic light, namely as shown in (a) in fig. 2-10, a storehouse P is connected with a traffic light bank₁As transition t₂And the library post P₂As the output library of the transition; further store P₂As transition t₃Is inputtedA depot and a depot P₃As the output library of the transition; further store P₃As transition t₁And the library post P₁As the output library of the transition;

further, a control library is added among the three-phase traffic lights, so that mutual exclusion change among the traffic lights is realized, and the method specifically comprises the following steps: adding control stores P₁₆As S_swTransition in phase t₂Output depot of, simultaneously P₁₆As S_weTransition in phase t₄The input library of (a); in phase S_weAnd phase S_esAdds a control depot P in between₁₇As transition t₅As the transition t at the same time₇The input library of (a); adding control stores P₁₄As S_swTransition in phase t₁And P of the output depot₁₄As S_weTransition in phase t₅The input library of (a); in phase S_swAnd phase S_esPhase S_weAnd phase S_esRespectively add control stores P in between₁₃And P₁₅Depot P₁₃As transition t₁The output depot of (1) is simultaneously used as t₈Input depot, depot P₁₅As transition t₄The output depot of (1) is simultaneously used as t₈The input library of (a);

3-4, establishing Petri network models corresponding to different emergency scenes on the basis of the models established in the step 3-3, specifically:

when an emergency vehicle enters a T-shaped intersection to transit T₁₀Is triggered, its output depot P₁₀The Token number in the system is added with 1, and the Token can prevent the traffic light from changing before the emergency vehicle leaves the system, so as to prevent the emergency vehicle from changing by P₁₀Exponential distribution triggered transitions t connected as input libraries₁₁，P₁₁The method realizes the connection between a control system and an original traffic light system, and adds a transition t on a model₁₂To realize the restoration of the traffic light control system to the original state after the emergency vehicle leaves the intersection, and to add the depot P₁₂To effectively control the number of system emergency vehicles to be 1, depot P₁₁Including its connection to the control system and its connection to the original traffic light system, in particular, the depot P₁₁As transition t₂The output depot of (A) is simultaneously used as S_esPhase transition t₇(or S)_wePhase transition t₄) The input depot, depot P₁₁And P₁₂As transition t₁₂When the emergency vehicle leaves the intersection, the input depot of (1) triggers the transition t₁₂The system is brought into the operating state of the basic traffic light system. As shown in fig. 2(a) to 10(a), the Petri net models corresponding to all the emergency scenes are established according to the above process, and the Petri net model corresponding to each emergency scene realizes the following preemption control on emergency vehicles at the T-shaped intersection:

(1) FIG. 2(a) is an emergency scenario (R)_sw，G_we，R_es) Depot R_sw，G_weAnd R_esIs marked. The emergency scene indicates a green light G when the EV enters the intersection_weAnd the operation is continued. The continuous operating time of the green lamp was 60 seconds. In FIG. 2(a), p₄，p₁₃，p₁₄And p₁₅All have a tobken. Collisions may occur during this process. To avoid the occurrence of an emergency scenario, a transition t is triggered₅Before, it must be passed through the trigger transition t₁₁ ⁽¹⁾Will store p₄(p₁₃，p₁₄，p₁₅) Token moves to a depot p₅(p₁₁) In (1). The above operation indicates that the sensor detects EV before the green light changes to yellow. The model presented herein can change the phase of a traffic signal light in a short time. The traffic light then changes from green to yellow. Slave depot p₄，p₁₃，p₁₄And p₁₅Delete a tokken and then move one to a depot p₅. This situation indicates that the EV is not present for the duration of the green light, which also means that the situation is safe. The reachability graph and time information for this emergency scenario is shown in FIG. 2(b), R (M)₀)＝{M₀,M₁,M₂,M₃,M₄,M₅,M₆,M₇,M₈,M_9i,M_9h,M₁₀,M₁₁,M₁₂}。

(2) FIG. 3(a) is an emergency scenario (R)_sw，R_we，G_es) Depot R_sw，R_weAnd G_esIs marked. The emergency scenario representation indicates that when the EV enters the intersection, a green light (i.e., depot G)_we) And the operation is continued. The duration of the green light was 60 seconds. In FIG. 3(a), library p₇，p₁₃And p₁₅One for each. Collisions may occur during this period. To avoid this, the situation must be avoided by the step of₅Pre-trigger transition t₁₁ ⁽²⁾Will store p₇(p₁₃，p₁₅) Token in (1) moves to a depot p₈(p₁₁) In (1). It indicates that the sensor detects an EV before the green light normally turns yellow. The proposed model can prompt traffic lights to change their phase in a short time. The traffic light then turns yellow. Place of bank p₇，p₁₃And p₁₅One transferred to the depot p₈. This situation indicates that the EV is not present for the duration of the green light, which also means that the situation is safe. Its reachable graph with time information is shown in FIG. 3(b), R (M)₀)＝{M₀,M₁,M₂,M₃,M₄,M₅,M₆,M₇,M₈,M_9d,M_9b,M₁₀,M₁₁,M₁₂}。

(3) FIG. 4(a) shows an emergency scene (Y)_sw，R_we，R_es) Storehouse Y_sw，R_weAnd R_esIs marked. The emergency scenario indicates that when the EV is approaching the intersection area, the red light (R)_we) Changed to green light (G)_es). If the traffic light is not controlled, a very urgent situation will occur. Emergency situations are avoided by changing the control system. Here, when the EV approaches the intersection area, the pool p should be removed₁₃，p₁₄And p₁₆Of (1). And move the Token to the depot p₁₂. Then move it to the depot R_swAnd finally move to the depot G_sw. Next, when the EV passes (transmit t)₁₀) Making a businessIn the fork region, a transition t can be emitted₂. Notably, p is₁₃，p₁₄，p₁₅，p₁₆And p₁₇Is used to coordinate the alternation of traffic lights according to certain rules. Depot p₁₃，p₁₄，p₁₅，p₁₆And p₁₇Controlling the transition t separately₁(t₈)，t₁(t₅)，t₄(t₈)，t₂(t₄) And t₅(t₇). For example, when an EV approaches an intersection, a transition t is triggered₁₁ ⁽³⁾. Therefore, the traffic control system can effectively avoid emergency situations. Here, in FIG. 4(b), R (M) is shown₀)＝{M₀,M₁,M₂,M₃,M₄,M₅,M₆,M₇,M₈,M_9e,M₁₀,M₁₁,M₁₂,M₁₃}。

(4) FIG. 5(a) shows an emergency scenario (R)_sw，R_we，R_es) Depot R_sw，R_weAnd R_esIs marked. The emergency scenario shows that when the EV enters the intersection area, the red light (R)_we) Turning into a green light. Note that all three traffic lights are red, which lasts two seconds. This may lead to the occurrence of an emergency scenario. Two control methods are proposed here to avoid the occurrence of emergency scenarios. The first strategy is to use an unlabeled library p₁₆To prevent transition t₄And (4) transmitting. It shows that the proposed model can ensure that the red light remains unchanged until the EV has completely passed. The specific operation of our model for solving emergency scenarios is as follows. When an EV enters a junction and transitions to t₁₁ ⁽³⁾At the time of transmission, depot p₁₃，p₁₄And p₁₆All the tobuken in (1) are removed. At this time, p₁₆Becomes empty, and p₁₁Is marked. After 5 seconds, the traffic light should be red (R)_sw) To green (G)_sw). At the same time, mark the place p₁₁To prevent transition t₂Is transmitted. This means that the traffic phase cannot change as the emergency vehicles pass through the intersection area. Thus, can avoidEmergency situations in front of the eye. Note that the second is the same as previously mentioned, i.e. fig. 2 (a). In this example, R (M) is shown in FIG. 5(b)₀)＝{M₀,M₁,M₂,M₃,M₄,M₅,M₆,M₇,M₈,M_9g,M_9i,M₁₀,M₁₁}。

(5) FIG. 6(a) shows an emergency situation (R)_sw，R_we，R_es) (Change of phase), depot R_sw，R_weAnd R_esIs marked. The emergency scenario indicates a red light (R) when the EV enters the intersection area_es) The strain was green. Note that both traffic lights are red for two seconds. It shows a possible emergency scenario. Two control strategies are proposed here to avoid this. The first strategy is to use unlabeled libraries p₁₇To prevent transition t₇And (4) transmitting. It shows that the proposed model can ensure that the traffic light continues to be red until the EV passes. We propose a detailed operational explanation of the model as follows. When t is₁₁ ⁽⁴⁾On transmission (i.e. entry of EV into crossover region), p₁₃，p₁₅And p₁₇All the tobuken in (1) are removed. At this time, p₁₇Becomes empty, and p₁₁Is marked. After 5 seconds, the traffic phase should be red (R)_sw) To green (G)_sw). At the same time, mark the place p₁₁To prevent transition t₂And (4) transmitting. This means that the phase of the traffic light cannot be changed when the EV passes through the crossing area. Thus, the occurrence of an emergency scene can be avoided. Note that the next one is the same as previously mentioned, i.e. fig. 3 (a). In this example, we can see R (M) in FIG. 6(b)₀)＝{M₀,M₁,M₂,M₃,M₄,M₅,M₆,M₇,M₈,M_9f,M_9d,M₁₀,M₁₁}。

(6) FIG. 7(a) shows an emergency situation (R)_sw，R_we，R_es) Depot R_sw，R_weAnd R_esMarked, both red lights are on, and the duration of this state is 2 seconds. The emergency scene is connected with the EVNear the intersection region, depot p₁₀Among them is tobken. This means that the sensor detects the EV during this time. At this time, t is triggered₁₀Let p be₁₀One tokken was obtained. M₀(0,0,1,0,0,1,0,0,1,0,0,0, 0) is an initial mark. It is noted that when the system is in state M₀When two transitions (t) are enabled₁，t₁₁ ⁽⁵⁾). At this time, by considering their transition delay time, when t₁₁ ⁽⁵⁾Is less than t₁Delay time of t₁₁ ⁽⁵⁾Will be triggered. At the same time, tobken moves immediately into p₁₁And p₁₂. At the triggering transition t₁Then, depot G_sw，p₁₃And p₁₄Each of which receives a token. That is to say if the library p₁₁If there is one Token, the transition t cannot be triggered₂. The reachability graph with timing information is shown in fig. 7 (b). It demonstrates the activity and reversibility of the system model. Apparently, R (M)₀)＝{M₀,M₁,M₂,M₃,M₄,M₅,M₆,M₇,M₈,M_9a,M_9c,M₁₀,M₁₁}。

(7) FIG. 8(a) shows an emergency situation (R)_sw，R_we，Y_es) Depot R_sw，R_weAnd Y_esIs marked. The emergency scenario indicates that the traffic light is yellow when the EV enters the intersection area (Kunstoff Y)_es). The system model does not seem to do any control work, as the traffic light should be changed to red as soon as possible. The reachability graph with time information is shown in fig. 8 (b). Apparently, R (M)₀)＝{M₀，M₁,M₂,M₃,M₄,M₅,M₆,M₇,M₈,M_9b,M₁₀,M₁₁,M₁₂,M₁₃}。

(8) FIG. 9(a) shows an emergency situation (R)_sw，Y_we，R_es) Depot R_sw，Y_weAnd R_esIs marked. The emergency scenario shows a yellow light (Kunstoff Y) when the EV enters the intersection_we) Is in progress. In this case, p is as we can see in FIG. 8(a)₁₃，p₁₅And p₁₇One for each. To avoid this, at trigger t₆Must be preceded by a trigger t₁₁ ⁽⁶⁾Will store p₁₃(p₁₅，p₁₇) Token in (1) moves to a depot p₁₁In (1). The reachability graph with time information is shown in fig. 9 (b). Apparently, R (M)₀)＝{M₀,M₁,M₂,M₃,M₄,M₅,M₆,M₇,M₈,M_9h,M₁₀,M₁₁,M₁₂,M₁₃}。

(9) FIG. 10(a) shows an emergency scene (G)_sw，R_we，R_es) Depot G_sw，R_weAnd R_esIs marked. Fig. 10(a) shows that the traffic signal lights are red lights in the east-west direction (east-south direction)/west-south direction traffic directions (courtyard R), respectively_weAnd R_es) Green light (Ku Shi G)_sw) Then, a collision may occur. If it is changed to t₂And t₁₁ ⁽⁷⁾Which will be triggered first are all enabled? This means that in the process the traffic lights should be changed to avoid emergency situations. Case I (emission t)₁₁ ⁽⁷⁾) Indicates that when the EV approaches the intersection, Token is put in t₁₁ ⁽⁷⁾To prevent t₂And (4) transmitting. Therefore, the phase of the traffic light should not be changed. It indicates that the traffic light signal is still red in the east-west (southeast) direction. Case II (emission t)₂) As discussed in fig. 10 (a). The reachable graph is shown in FIG. 10 (b). Apparently, R (M)₀)＝{M₀,M₁,M₂,M₃,M₄,M₅,M₆,M₇,M₈,M_9c,M_9e,M₁₀}。

Generating respective reachability graphs as shown in fig. 2(b) to 10(b) according to the Petri net models corresponding to different emergency scenes as shown in fig. 2(a) to 10(a), completing analysis of the reachability graphs according to the models of different phase specific emergency scenes, and when an emergency vehicle enters an intersection, according to the shape of a traffic light when the emergency vehicle arrivesState, for avoiding collision, by triggering transition t₁₁ ⁽ⁱ⁾(i is an integer between 0 and 9) changing the number of the Tokens in the library, suppressing the change of the traffic lights, and generating an reachable graph of the emergency control system according to the analysis of each state.

The algorithm for constructing the reachability graph is as follows:

step 4, combining Petri network models corresponding to different emergency scenes to construct a T-shaped intersection emergency vehicle preemption control system, which specifically comprises the following steps:

arcs of all libraries or arcs of all libraries in a specific emergency scene are integrated into a complete control diagram, namely a T-shaped intersection emergency vehicle preemption control system is formed as shown in FIG. 11.

Based on the system shown in fig. 11, a corresponding reachable graph is generated, as shown in fig. 12, specifically as follows: the basic idea of constructing a reachability graph is as follows: first, an initial identifier M₀Is a starting node; setting the current identifier as M, triggering each transition T enabled under the current identifier, and performing the following judgment processing on the obtained identifier M': if M 'is the existing mark on the reachable graph, adding M to the arc of the existing mark M'; if M ' is larger (or smaller) than a certain mark in the existing reachable graph, judging whether M ' is increased (or decreased) according to the weight value on the corresponding arc, if so, abstracting M ' and the existing mark into a type of mark, and marking the increased corresponding component into a form of ' weight value x n '; if M ' is different from any existing identification, M ' is a new reachable identification, and the arc of M ' is added. The algorithm continues until none of the transitions are enabled or any of the enabled transitions can generate a new reachable identity.

Firstly, according to the reachable graphs of different emergency scenes, connecting the reachable graphs into an integral analysis graph according to a transition triggering rule, namely, on the basis of the reachable graph of one situation, judging whether the marks of other situations are the existing marks on the existing reachable graph or not, if so, connecting the marks into an integral analysis graph according to the transition triggering ruleAdding arcs between the two identifiers, and finally connecting all the reachable graphs into a complete reachable graph; and analyzing two paths on the reachability graph when an emergency vehicle enters the intersection according to the overall reachability graph: m₀t₁₁ ⁽⁵⁾M₁₀t₁₂M₂₂t₁M₁₂t₂M₂₀t₃M₂₅t₄M₃₂t₁₁ ⁽¹⁾M₄₁t₁₂M₄₀t₉M₀And M₀t₁₁ ⁽⁵⁾M₁₀t₁₂M₂₂t₁M₁₂t₂M₂₀t₃M₂₅t₄M₃₂t₅M₃₅t₆M₃₉t₇M₄₂t₁₁ ⁽²⁾M₁₃t₁₂M₄₅t₉M₀。

Analyzing the activity and reversibility of the T-shaped intersection emergency vehicle preemption control model obtained in the embodiment according to the reachability graph obtained in the step 4, specifically as follows:

in the known network system (N, M)₀) In, if

M' [ t >, then M₀The transition T ∈ T of (c) is alive. Consider a bounded network system (N, M)₀) And can reach graph G (N, M)₀). If and only if an edge marker t belongs to G (N, M)₀) When each traverse component of (1), then M₀The transition T ∈ T of (c) is alive. (N, M)₀) Is alive, if and only if for

The edge marker t belongs to G (N, M)₀) Each traverse component of (a). The reachability graph can well judge the activity problem. Reacting on the reachable graph, as long as the graph has leaf nodes, the Petri net is not alive. If all reachable identities can be returned to the initial identity M₀Then the Petri net system is reversible. That is, if G (N, M)₀) Is in strong communication withDrawing, then (N, M)₀) Is reversible.

The method can effectively avoid the situation that the emergency vehicles conflict at the T-shaped intersection, improve the traffic efficiency of the intersection and effectively shorten the time required by the emergency vehicles to reach the destination.

Claims

1. A T-shaped intersection emergency vehicle preemption control method based on a timed Petri network is characterized by comprising the following steps:

step 2, dividing different emergency scenes according to the states of traffic lights when the emergency vehicles reach the T-shaped intersection; the method specifically comprises the following steps:

(1) the instant emergency scene, i.e. the case where the advancing direction of the emergency vehicle is perpendicular to the traffic flow, includes the following 5: (S)₃₁R，S₁₂G，S₂₃R)，(S₃₁R，S₁₂R，S₂₃G)，(S₃₁Y，S₁₂R，S₂₃R)，(S₃₁R，S₁₂R，S₂₃R) and (S)₃₁R，S₂₃R，S₁₂R); wherein (S)₃₁R，S₁₂R，S₂₃R) is S₁₂R will change to green state, (S)₃₁R，S₂₃R，S₁₂R) is S₂₃R will change to a green state;

(2) indirect emergency scenarios, i.e. situations in which the direction of advance of the emergency vehicle is parallel to the flow of trafficThe method comprises the following 4 types: (S)₃₁R，S₁₂R，S₂₃R)，(S₃₁R，S₁₂R，S₂₃Y)，(S₃₁R，S₁₂Y，S₂₃R) and (S)₃₁G，S₁₂R，S₂₃R)；

aiming at different emergency scenes, when a timing Petri network is utilized to model a T-shaped intersection emergency vehicle preemption control system:

the method for expressing the rule in the traffic light control system by using the relation arc between the Petri network middle place and the transition specifically comprises the following steps: in the three-phase control of the T-shaped intersection, if a green light of one traffic light is in a working state, red lights of all other traffic lights are in a working state;

the method comprises the following steps:

step 3-2, setting a fixed time interval for triggering the Petri network transition, specifically: the red light duration of each intersection lamp of the T-shaped intersection is T₁Green light duration of t₂Yellow light persistenceTime t₃(ii) a Wherein t is₁、t₂、t₃The value of the traffic flow is freely determined according to the actual traffic conditions of different T-shaped intersections, namely the traffic flow;

step 3-3-2, adding a control library among the three-phase traffic lights, specifically: adding control stores P₂₁As S₃₁The phase traffic light control structure comprises an output library for green light duration transition, and P is converted into₂₁As S₁₂The phase traffic light control structure comprises an input library of red light duration transition; in phase S₁₂And phase S₂₃Adds a control depot P in between₂₂(ii) a Adding control stores P₁₁As S₃₁The phase traffic light structurally comprises an output bank of red light duration transitions, and P is₁₁As S₁₂The phase traffic light control structure comprises an input library of green light duration transition; in phase S₃₁And phase S₂₃Phase S₁₂And phase S₂₃Respectively add control stores P in between₁₂And P₁₃；

3-4, building Petri network models corresponding to different emergency scenes on the basis of the models built in the step 3-3; the method specifically comprises the following steps:

in emergency scene (S)₃₁R，S₂₃G，S₁₂R) case is as an example: depot S₃₁R，S₂₃G，S₁₂R，P₁₂And P₁₃The Token number in (1) is assumed that the arrival direction of the emergency vehicle is S₃₁At this time, an emergency occurs, and the exponential distribution triggers transition T_sWith S₂₃G，P₁₂And P₁₃As its input library, S₂₃Y、P_mAnd P_qAs its output depot, by triggering a transition T_sThe occurrence of an emergency scene is effectively avoided; depot P_qAs S₃₁The phase includes an output library of green duration transitions, and is used as S₂₃Input post including red light duration transitions on phase, post P_qAnd P_mAs transition T_eBy touching when the emergency vehicle leaves the T-junctionHair transition T_eRestoring the traffic light to an initial normal operating state, thereby establishing an emergency scene (S)₃₁R，S₂₃G，S₁₂R) corresponding Petri net model; establishing Petri network models corresponding to all emergency scenes in the step 2 in a similar manner;

2. The method for controlling emergency vehicle preemption at a T-junction based on a timed Petri network as claimed in claim 1, wherein the maximum capacity value of all libraries in the Petri network is set to 1 in step 1.

3. The T-junction emergency vehicle preemption control method based on timed Petri nets of claim 1, wherein the step 4 combines Petri net models corresponding to different emergency scenes to construct a T-junction emergency vehicle preemption control system, which realizes T-junction emergency vehicle preemption control, and specifically comprises the following steps:

and integrating arcs from all libraries to the transition or arcs from the libraries to the transition in the Petri network model corresponding to all emergency scenes into a complete control chart, thereby constructing a T-shaped intersection emergency vehicle preemption control system, and realizing T-shaped intersection emergency vehicle preemption control by the system.