An emergency vehicle optimal path planning method considering priority potential

Abstract

This invention relates to an optimal route planning method for emergency vehicles that considers priority potential. First, a weighted directed graph of the urban road network is constructed. Based on road segment information, the comprehensive impedance of basic road segments is calculated, and a comprehensive priority passage potential index is calculated based on the spatial priority capacity of road segments and the time priority capacity of downstream intersections. This index is directly incorporated into the comprehensive impedance of basic road segments to form a priority potential-corrected comprehensive impedance. This priority potential-corrected comprehensive impedance is used as the path search impedance. A set of candidate emergency vehicle routes is generated using the K-shortest path algorithm, and the optimal execution path and alternative paths are selected based on path safety constraints and path reliability constraints. During the operation of the emergency vehicle, the road network status information within the area associated with the current execution path is monitored. When the status change reaches a preset trigger condition, rolling replanning is performed on the suffixes of unexecuted paths, and the current execution path is replaced based on the improvement magnitude of the comprehensive impedance and the path deviation rate.

Description

Technical Field

[0001] This invention belongs to the field of emergency vehicle route planning technology, specifically relating to an optimal route planning method for emergency vehicles that considers priority potential. Background Technology

[0002] Emergency vehicles are a key transportation carrier in the urban public safety emergency response system, and their route planning efficiency directly affects the effectiveness of casualty treatment, fire fighting, accident handling, and disaster emergency response. With the continuous growth of urban traffic demand, urban road networks often experience tidal congestion, local queue spread, road construction, traffic control, and sudden accidents. Emergency vehicles are easily affected by the operating status of regular vehicles, the control status of intersections, and changes in local road conditions during mission execution, leading to problems such as traffic obstruction, route failure, or frequent detours in the actual implementation of traditional route planning results.

[0003] Most existing emergency vehicle route planning methods are based on static or weakly dynamic road network information, typically employing classic path search methods such as Dijkstra's, A*, and K-shortest path, using segment length, average travel time, or road grade as primary edge weight indicators. While these methods can quickly generate feasible paths under given road network conditions, they fail to adequately utilize dynamic traffic information such as traffic volume, queue length, average operating speed, construction closures, and abnormal traffic conditions, making it difficult to accurately reflect the real-time travel costs of emergency vehicles in the actual road network. When urban road conditions change rapidly, path results generated based on static edge weights or single time weights are prone to becoming out of touch with the real traffic environment, failing to meet the high timeliness and adaptability requirements of emergency rescue.

[0004] On the other hand, existing methods, when considering the priority passage of emergency vehicles, typically handle route planning and subsequent priority control separately. That is, candidate routes are generated first, and then it is determined whether signal priority, yielding, or temporary traffic organization conditions are met based on these candidate routes. This type of method fails to simultaneously consider spatial priority conditions at the road segment level and temporal priority conditions at the intersection level during the route generation stage. As a result, while the generated route may be more advantageous in terms of basic traffic costs, it may not necessarily facilitate the implementation of subsequent priority passage measures, thus reducing the consistency and feasibility between the route planning results and the actual priority control conditions.

[0005] Furthermore, existing methods typically lack a rolling update mechanism for the regions associated with the current execution path during the dynamic execution phase. Some methods only recalculate the entire path at fixed intervals, or directly replace it with a new path after changes in the road network, without distinguishing between executed and unexecuted paths, and also lacking a joint assessment of the benefits and disturbances of path switching. This leads to two problems: first, when local state changes are insufficient to substantially affect the current execution path, ineffective replanning may still be triggered; second, when the new path is only a minor improvement over the current path, frequent path switching increases execution disturbances, which is detrimental to the stable passage of emergency vehicles.

[0006] Therefore, there is an urgent need for a new emergency vehicle route planning method that can integrate subsequent priority passage conditions into the route planning process itself based on dynamic traffic state perception, and perform event-triggered rolling replanning of unexecuted route parts in combination with the status changes of the currently executed route associated areas during operation, while taking into account the benefits of route update and the stability of route switching, so as to improve the adaptability, continuous optimization capability and practical feasibility of emergency vehicle route planning in dynamic traffic environments. Summary of the Invention

[0007] To address the problems in emergency vehicle route planning, such as insufficient dynamic traffic status perception, disconnect between route planning and subsequent priority conditions, priority conditions being determined only after candidate routes are generated, and untimely route updates or frequent rerouting in scenarios such as sudden congestion, construction closures, and rapid growth of local queues, this invention provides an optimal route planning method for emergency vehicles that considers priority potential.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by this invention is: an optimal route planning method for emergency vehicles considering priority potential, comprising the following steps:

[0009] The urban road network is divided into road segment modules and intersection modules. The static and dynamic attribute characteristics of each road segment module and intersection module are obtained, and a weighted directed graph of the urban road network modules is constructed.

[0010] The basic road segment comprehensive impedance is calculated based on the dynamic traffic conditions of the road segment, and the comprehensive priority passage potential index is calculated based on the spatial priority capacity of the road segment and the time priority capacity of the downstream intersection. The comprehensive priority passage potential index is directly incorporated into the basic road segment comprehensive impedance to form the priority potential modified road segment comprehensive impedance.

[0011] The comprehensive impedance of the priority potential modified road segment is used as the path search impedance, and the K-shortest path algorithm is used to generate a set of candidate paths for emergency vehicles.

[0012] The candidate path set is filtered based on path security constraints and path reliability constraints to determine the optimal execution path and alternative paths at the current moment.

[0013] During the operation of emergency vehicles, the road network status information in the area associated with the current execution path is continuously monitored. When the change in road network status information reaches the preset trigger condition, the unexecuted path suffix is ​​rolled and replanned based on the current position of the emergency vehicle as the new starting point, while freezing the prefix of the executed path.

[0014] The updated path obtained from the rolling replanning is compared with the current execution path. When the overall impedance improvement of the updated path relative to the current execution path reaches a preset benefit threshold, and the path deviation of the updated path relative to the current execution path does not exceed a preset deviation threshold, the updated path replaces the current execution path; otherwise, the current execution path remains unchanged.

[0015] Preferably, the static attribute characteristics of the road segment module include at least the road segment length, the number of lanes in the road segment, the road speed limit, the road grade, and whether it has spatial priority control or cooperative control facilities; the static attribute characteristics of the intersection module include at least whether it is a signal-controlled intersection and whether it has signal priority or vehicle-road cooperative control facilities. The dynamic attribute characteristics include at least traffic volume, queue length, average operating speed, construction closure status, abnormal traffic status, congestion status, and other status information reflecting changes in traffic operation.

[0016] Preferably, the expression for the comprehensive impedance of the priority potential modified road segment is as follows:

[0017]

[0018] in, For road section At any moment Priority potential for correcting the overall impedance of the road segment; For road section At any moment The overall impedance of the basic road section; For the node Pointing to node directional road sections; and These are adjacent nodes in the road network; For emergency vehicles to enter the road section The moment; The priority potential correction coefficient satisfies... ; For the road section The relevant comprehensive priority passage potential index meets the requirements. .

[0019] The above expression shows that the present invention does not determine the priority conditions after the candidate path is generated, but directly incorporates the comprehensive priority passage potential index into the path impedance calculation process, so that the candidate path generation stage is simultaneously affected by the subsequent priority passage conditions, thereby making the path planning result naturally biased towards the path that is easier to implement priority passage.

[0020] Preferably, the comprehensive impedance of the basic road section The expression is as follows:

[0021]

[0022] in, For road section Length; For road section At any moment Queue length; For road section At any moment The traffic volume index is preferably the number of vehicles passing through the detection section of the road segment per unit time. In alternative implementations, the saturation index obtained by converting traffic volume can also be used. Traffic volume impact adjustment coefficient, which is a pre-calibrated constant; For road section At any moment The average operating speed; To avoid extremely small positive numbers with a denominator of zero.

[0023] The technical implications of the aforementioned basic road segment comprehensive impedance are as follows: the longer the road segment, the greater the queue length, and the higher the traffic volume, the greater the basic passage cost for emergency vehicles passing through that road segment; conversely, the higher the average operating speed, the lower the basic passage cost. This formula directly uses readily available road segment-level traffic data to construct the basic impedance, avoiding over-reliance on microscopic trajectory variables that are difficult to obtain stably, thereby improving the feasibility of practical deployment.

[0024] Preferably, the comprehensive priority passage potential index It is determined by both the road segment spatial priority capacity and the downstream intersection time priority capacity, and its expression is as follows:

[0025]

[0026] in, For road section At any moment Priority capacity for road segment space; For downstream nodes At the intersection at time Intersection time priority capability; This is a balance coefficient between road segment space priority capacity and intersection time priority capacity, satisfying... .

[0027] This formula breaks down the subsequent priority passage conditions for emergency vehicles into two categories: "spatial priority conditions at the road segment level" and "time priority conditions at the intersection level." It then maps these conditions to the path search impedance using a unified index, enabling the path planning stage to simultaneously perceive potential conditions that can be used for temporary clearance, priority passage, and time priority control.

[0028] Preferably, the road segment spatial priority capability The expression is as follows:

[0029]

[0030] in,

[0031]

[0032]

[0033] in, For road section Whether a binary variable possesses the basic conditions for spatial priority; For road section The identifier variable indicates whether the facility has space priority control or collaborative control facilities; if it does, the value is 1, otherwise it is 0. For road section The number of lanes; For road section At any moment Spatial priority potential; To determine the maximum number of lanes on road sections within the study area; To determine the normalized upper bound of the queue length of road segments within the study area, the preferred upper bound is the maximum observed value or a preset upper limit value of the queue length of road segments within the statistical period. For road section Speed ​​limits.

[0034] In this formula, the two variables This is used to determine whether a road segment has the basic possibility of implementing space priority in terms of facility conditions and lane resources; only road segments with facility support and no less than two lanes are included in the subsequent space priority potential calculation.

[0035] Space priority potential middle, Characterizes the proportion of remaining lane resources that can be used for space-priority organization; This characterizes the inhibitory effect of queue length on spatial priority potential; the longer the queue, the smaller this value. This value represents the current smoothness of traffic flow on a road segment; the higher the speed, the larger the value. Therefore, it can effectively assess the potential for implementing space-priority strategies on a road segment under realistic data conditions.

[0036] Preferably, the intersection time priority capability The expression is as follows:

[0037]

[0038] in,

[0039]

[0040]

[0041] in, Intersection Whether a binary variable meets the basic condition of time priority; For nodes Whether it is an identifier variable for a signal-controlled intersection; if yes, set to 1; otherwise, set to 0. Intersection The variable indicates whether signal priority or vehicle-road cooperative control facilities are available; if so, the value is 1, otherwise it is 0. Intersection At any moment Time-priority potential; Intersection Emergency vehicle approach direction approach lane at time Queue length; This is the normalized upper bound for the queue length at the intersection entrance lanes; For emergency vehicles approaching from the corresponding approach lane or adjacent approach section at the designated time. The average operating speed; For the speed limit of the adjacent road section; superscript This indicates the traffic volume of the approach lane or adjacent road segment in the direction of an emergency vehicle approaching the intersection.

[0042] In this formula, the two variables This is used to determine whether an intersection has the basic possibility of implementing time priority in terms of control methods and facility conditions; only signal-controlled intersections with corresponding priority control facilities will proceed to subsequent time priority potential calculations.

[0043] In time priority potential middle, Characterize the inhibitory effect of entrance lane queue length on time priority; This characterizes the current smoothness of traffic flow on adjacent road segments. Therefore, readily available real-world queuing and speed data can be used to assess the potential for implementing time-priority measures at intersections.

[0044] After generating the priority potential modified road segment comprehensive impedance, it is used as the path search impedance, and the K-shortest path algorithm is used to generate a set of candidate routes for emergency vehicles. Unlike the existing technology that first generates candidate routes and then determines priority conditions, this invention introduces priority passage potential in the path search stage, so that the candidate route generation process itself is directly affected by subsequent priority conditions.

[0045] Preferably, the path safety constraint employs a product-type risk amplification method to construct a dynamic risk index for road segments, and calculates a cumulative path risk index based on the dynamic risk index for road segments, the expression of which is as follows:

[0046]

[0047]

[0048]

[0049] in, For road section At any moment The dynamic risk index; For road section The normalized value of historical accident risk; For road section At any moment Normalized values ​​of risks associated with abnormal construction, closure, or traffic conditions; For road section At any moment The real-time congestion risk normalized value; For road section At any moment The real-time volatility risk normalized value; This is a candidate path from the starting point to the target point; Emergency vehicle access routes Upper section The moment; For path The cumulative risk index; This is the threshold for the path risk index.

[0050] in, The frequency of historical traffic accidents on the road section was obtained by minimum-maximum normalization. It is obtained by mapping or normalizing the road section's construction status, closure status, traffic control status, or other abnormal traffic events. It is obtained by normalizing at least one of the following: road segment congestion delay index, speed reduction rate, or traffic efficiency reduction rate.

[0051] The real-time volatility risk normalization value The expression is as follows:

[0052]

[0053] in, For the update cycle.

[0054] The purpose of adopting the product-type risk amplification method is to amplify the comprehensive risk of a road segment when it is simultaneously in an unfavorable state in multiple dimensions such as accident risk, abnormal state risk, congestion risk and fluctuation risk, thereby avoiding the underestimation of high-risk road segments due to the averaging of a single risk item.

[0055] Preferably, the path reliability constraint is constructed using a combination of expected arrival time and time buffer, and its expression is as follows:

[0056]

[0057] in, For emergency vehicles entering the section of road The moment The estimated travel time for this section of the road; For path Time buffer; This represents the maximum acceptable arrival time threshold for emergency vehicles.

[0058] The path time buffer The redundancy used to characterize the uncertainty of path travel time is determined based on at least one of the following factors: total path length, historical travel time fluctuation level of the path, and number of critical nodes passed through the path.

[0059] In a preferred embodiment, the path time buffer item It can be represented as:

[0060]

[0061] in, For path The total length; For path Number of key nodes passed through; and This is the pre-calibrated buffer adjustment coefficient.

[0062] After completing the path safety and path reliability screening, candidate paths that meet the risk constraints and reliability constraints are obtained, and the optimal execution path and alternative paths at the current moment are determined from them.

[0063] Preferably, the rolling replanning is performed by freezing the prefix and optimizing the suffix, and its expression is as follows:

[0064]

[0065] in, For a moment The update execution path; Deadline Executed or locked path prefixes; For a moment Path suffix obtained through rolling optimization; This indicates a path concatenation operation.

[0066] The above description indicates that the present invention does not repeatedly recalculate the entire path globally, but optimizes only the suffix of the unexecuted path while keeping the prefix of the executed path unchanged, thereby improving the practical feasibility of dynamic path updates.

[0067] Preferably, the triggering condition for the rolling replanning is determined by the change in the status of the comprehensive road network information within the area associated with the current execution path, and its expression is as follows:

[0068]

[0069] in, The current execution path and its adjacent areas of influence Changes in the overall status of the road network within the area; The threshold for triggering replanning; It is a state vector; It is the difference between the state vectors at two different time points; Let be the norm of the state vector difference.

[0070] The state vector includes at least one or more of the following: queue length, average operating speed, traffic volume, construction closure status, and route risk status.

[0071] This formula indicates that the present invention does not trigger replanning every time there is a tiny change in the state of the entire network, but rather performs event-triggered dynamic updates based on the current execution path and its adjacent affected areas, thereby reducing invalid replanning.

[0072] Preferably, after triggering rolling replanning, the path suffix Determine as follows:

[0073]

[0074] in, This is the node corresponding to the current location of the emergency vehicle; For the target node; For a moment The set of remaining feasible nodes; To start from the current node To the target node The set of feasible suffix paths; To predict the window length; For path In the prediction window The average composite impedance within.

[0075] Wherein, the average composite impedance It can be represented as:

[0076]

[0077] in, For path At the predicted time The overall impedance is as follows.

[0078] This formula illustrates that the present invention considers the average combined impedance within the prediction window when optimizing suffix paths, rather than making update decisions based solely on the current state of a single point, thereby enhancing the foresight of dynamic path updates.

[0079] Preferably, the updated path and the current execution path satisfy the following benefit-deviation dual threshold switching condition:

[0080]

[0081] and

[0082]

[0083] in,

[0084]

[0085] in, The current execution path The overall impedance; To update the path The overall impedance; The minimum revenue threshold for path switching; This is the length-weighted path deviation rate between the current execution path and the updated path. For path The set of edges; This is a symmetric difference operation between two sets. For the edge The length of the corresponding road segment; This is the maximum allowable deviation threshold for path switching.

[0086] When both the aforementioned revenue threshold and deviation threshold conditions are met, the current execution path is replaced with the updated path; otherwise, the current execution path remains unchanged. By introducing dual constraints of revenue and deviation thresholds, this invention ensures the effectiveness of path updates while avoiding frequent route changes due to minor disturbances.

[0087] Compared with existing technologies, the beneficial effects of this invention are as follows: By directly introducing a comprehensive priority passage potential index into the comprehensive impedance of the basic road segment, this invention forms a priority potential modified comprehensive impedance of the road segment. This allows the generation process of emergency vehicle candidate routes to simultaneously consider subsequent spatial priority conditions and time priority conditions, rather than judging priority conditions after candidate routes are generated. This improves the consistency between the route planning results and subsequent priority passage implementation conditions. At the same time, this invention adopts an event-triggered rolling replanning mechanism oriented towards the currently executed route association area. It optimizes the suffix of unexecuted routes based on freezing the prefix of executed routes and controls route switching through a dual threshold of benefit and deviation. This extends emergency vehicle route planning from a one-time static route selection to a continuous optimization process that adapts to the dynamic traffic environment, enhancing the adaptability, stability, and practical feasibility of the route planning results. Attached Figure Description

[0088] Figure 1 This is a schematic diagram of the process of the present invention;

[0089] Figure 2 This is a preferred embodiment of the road network structure of the present invention. Detailed Implementation

[0090] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0091] This embodiment provides an optimal route planning method for emergency vehicles that considers priority potential, applied to an emergency rescue mission scenario within the road network of a city's core built-up area. In this scenario, emergency vehicles need to quickly, safely, and stably reach their destination from the starting point under conditions of dynamic congestion, local queue growth, construction closures, traffic control, or other abnormal traffic disturbances. During the execution process, unexecuted routes are continuously updated based on changes in the road network status.

[0092] In this embodiment, the urban road network consists of a set of nodes and a set of road segments. Specifically, as shown... Figure 2As shown, the urban road network in this embodiment includes 25 nodes and 38 effective two-way traffic segments, with nodes uniformly numbered from 0 to 24. Each node is equipped with signal control and collaborative control functions, and each road segment records at least the following attributes: segment length, number of lanes, road speed limit, traffic volume, average operating speed, queue length, construction / closure status, historical accident frequency, and abnormal traffic status. The emergency vehicle mission is set as follows: departing from node 0, proceeding to node 24 to perform a rescue mission. To improve emergency dispatch redundancy, the method output includes one optimal execution path and two alternative paths.

[0093] In this embodiment, the global parameters are set as follows: the road network status update step size is 120s; the priority potential correction coefficient is... The coefficient is 0.3; it represents the balance between road segment space priority capacity and intersection time priority capacity. 0.5; maximum acceleration of emergency vehicles The maximum deceleration of the emergency vehicle is 1.0 m / s². The value is 0.8 m / s². These parameters are used to control the network status update frequency, the priority potential correction magnitude, and the path update process during the dynamic execution phase.

[0094] I. Road Network Initialization

[0095] First, the city's road network is divided into road segment modules and intersection modules. The node table and road segment table are imported to create a weighted directed graph of the city's road network modules. The node table includes at least the node number, whether it has signal control attributes, and whether it has cooperative control attributes. The road segment table includes at least the starting node, ending node, road segment length, number of lanes, road speed limit, traffic volume, average operating speed, queue length, and construction / closure status. After importing, directed connections are established between nodes and road segments to provide foundational data for subsequent calculations of basic road segment impedance, calculation of comprehensive priority traffic potential, determination of path safety constraints, determination of path reliability constraints, and generation of candidate paths.

[0096] II. Calculation of Comprehensive Impedance of Basic Road Sections

[0097] For each section The comprehensive impedance of the basic road segment is calculated based on the current road segment length, queue length, traffic volume, and average operating speed. In this embodiment, the comprehensive impedance of the basic road section is calculated using the following formula:

[0098]

[0099] in, For road section Length; For road section At any moment Queue length; For road section At any moment Traffic volume indicators; Traffic volume impact adjustment coefficient; For road section At any moment The average operating speed; To avoid extremely small positive numbers with a denominator of zero.

[0100] The basic impedance of this road segment reflects the basic passage cost of emergency vehicles traversing the segment without considering subsequent priority passage conditions. When the segment length is long, the queue length is long, and the traffic volume is high, the basic passage cost of this segment increases; when the average operating speed is high, the basic passage cost of this segment decreases.

[0101] III. Calculation of Comprehensive Priority Traffic Potential

[0102] In this embodiment, the comprehensive priority passage potential index is used. Prioritizing road segment space Time priority capability at downstream intersections Jointly determined:

[0103]

[0104] in, This is the balance coefficient.

[0105] Road segment space priority capability The calculation is performed using the method of "basic condition determination × spatial priority potential":

[0106]

[0107] in,

[0108]

[0109]

[0110] in, Indicate whether the road segment has space priority control or collaborative control facilities; Indicates the number of lanes in a road segment; Indicates the maximum number of lanes in the study area; This represents the normalized upper bound of queue lengths in the study area. This indicates the speed limit for that section of road.

[0111] Therefore, only when a road segment has the relevant facilities and has no fewer than two lanes is it considered to have the basic possibility of implementing space priority on a macro level; on this basis, its space priority potential is determined by the proportion of remaining lane resources, the degree of queuing suppression, and the operating speed.

[0112] Intersection time priority capability The calculation is performed using the method of "basic condition determination × time priority potential":

[0113]

[0114] in,

[0115]

[0116]

[0117] in, Indicate whether the intersection is a signalized intersection; Indicate whether the intersection has signal priority or vehicle-road cooperative control facilities; Indicates the queue length at the approach lane for emergency vehicles; This represents the normalized upper bound of the queue length at the intersection entrance; This indicates the average speed of the emergency vehicle approaching from the corresponding approach lane or adjacent road segment. This indicates the speed limit for the corresponding road section.

[0118] IV. Calculation of Comprehensive Impedance for Priority Potential Modified Road Sections

[0119] In this embodiment, the comprehensive priority passage potential index is not determined after candidate paths are generated, but is directly incorporated into the path planning process itself. For each road segment, based on the comprehensive impedance of the basic road segment... and Comprehensive Priority Passage Potential Index The comprehensive impedance of the priority potential road section was obtained. :

[0120]

[0121] in, The priority potential correction factor is set to 0.3 in this embodiment.

[0122] Therefore, the edge weights used in the candidate path generation stage have already taken into account both the basic passage cost and the subsequent priority passage conditions, rather than first finding candidate paths and then determining whether they meet the priority conditions.

[0123] V. Construction of Path Security Constraints and Path Reliability Constraints

[0124] 1. Path security constraints

[0125] In this embodiment, path safety constraints are constructed using a product-based risk amplification approach. First, a dynamic risk index is calculated for each road segment:

[0126]

[0127] in, This represents the normalized value of historical accident risk. Normalized values ​​for risks related to abnormal conditions such as construction, closure, or traffic. This is a normalized value for real-time congestion risk; This is the normalized value for real-time volatility risk.

[0128] The normalized value of real-time volatility risk is calculated using the following formula:

[0129]

[0130] in, For the update cycle.

[0131] Then, for candidate paths The cumulative risk index of the route is obtained by summing the dynamic risk indices of each segment along the path:

[0132]

[0133] when If the candidate path satisfies the path security constraints, it is considered to meet the requirements; otherwise, it is discarded.

[0134] 2. Path reliability constraints

[0135] In this embodiment, the path reliability constraint is constructed using a combination of expected arrival time and time buffer:

[0136]

[0137] in, For emergency vehicles to enter the road section The estimated travel time for this section of the road at the current time; For path time buffer items; The maximum acceptable arrival time threshold.

[0138] In a preferred embodiment, the time buffer term can be represented as:

[0139]

[0140] in, This represents the total path length. This represents the number of critical nodes traversed by the path. and This is the buffer adjustment coefficient.

[0141] VI. Candidate Path Generation and Screening

[0142] Prioritize potential correction of the overall impedance of the road segment As the path search impedance, the K-shortest path algorithm is used to generate a candidate path set. In this embodiment, a total of 10 reachable paths that meet the road network connectivity conditions are generated. Then, path safety constraints and path reliability constraints are applied to each candidate path in the candidate path set, eliminating high-risk and low-stability paths, and retaining candidate paths that meet the constraints for subsequent optimal path and alternative path output. Representative path results in the initial candidate paths include: path [0,1,2,3,8,12,15,20,23,24] with an original time of 580.0s, a total risk value of 14, a reliability of 0.999, and a total weight of 1011.39; path [0,5,6,7,8,12,15,20,23,24] with an original time of 606.8s, a total risk value of 15, a reliability of 0.998, and a total weight of 1093.11.

[0143] Table 1 Initial Candidate Path Generation Results

[0144]

[0145] VII. Output of Optimal Path and Alternative Paths

[0146] For valid candidate paths that pass the constraint screening, they are comprehensively ranked based on travel time, security risk, and operational reliability, and the optimal execution path and alternative paths are output. In this embodiment, the output results are as follows:

[0147] The optimal path node sequence is: The original time was 580.0s, the optimized time was 444.0s, the optimization rate was 23.4%, the total risk value was 14, the reliability was 0.999, and the total weight was 818.79.

[0148] Table 2 Output results of optimal path and alternative paths

[0149]

[0150] The results above show that, under the premise of meeting safety and reliability constraints, the method of the present invention can simultaneously output the optimal path and two alternative paths. Among them, the optimal path has the shortest optimized travel time. Although the optimized travel times of alternative paths 1 and 2 are slightly longer, they still maintain high reliability and low risk, and can be used as alternative solutions when the main path is blocked.

[0151] VIII. Implementation Methods for the Dynamic Execution Phase

[0152] While the emergency vehicle travels along the current execution route, the road network status information within the area associated with the current execution route is continuously monitored. This status information includes at least queue length, average operating speed, traffic volume, construction closure status, and route risk status. Rolling replanning is initiated when the following triggering conditions are met:

[0153]

[0154] in, This refers to the state changes within the current execution path and its adjacent affected areas. The threshold for triggering replanning.

[0155] After triggering rolling replanning, instead of globally recalculating the entire path, the suffixes of unexecuted paths are updated while freezing the prefixes of already executed paths:

[0156]

[0157] in, For paths that have been executed or locked, To update the obtained path suffix.

[0158] Before replanning the route suffix, recalculate the comprehensive impedance of the basic road segments based on the latest status. Comprehensive priority passage potential index Combined impedance of priority potential modified road sections Then, starting from the node corresponding to the current position and targeting the end node, perform rolling replanning on the unexecuted path suffixes:

[0159]

[0160] in, For the path in the prediction window The average composite impedance within.

[0161] When the update path is obtained Then, it is compared with the current execution path. A comparison is performed; the updated path replaces the current execution path only if both of the following conditions are met:

[0162] and

[0163] in, The minimum revenue threshold, This is the maximum allowable deviation threshold for path switching. Dynamic execution allows for timely path updates when the state changes, while avoiding frequent route changes due to minor disturbances.

[0164] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, alterations, substitutions, or variations made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims

1. An optimal route planning method for emergency vehicles considering priority potential, characterized in that: Includes the following steps: S1. Divide the urban road network into road segment modules and intersection modules, obtain the static and dynamic attribute characteristics of each road segment module and intersection module, and construct a weighted directed graph of the urban road network modules. S2. Calculate the basic road segment comprehensive impedance based on the dynamic traffic state of the road segment module, and calculate the comprehensive priority passage potential index based on the road segment spatial priority capacity and the intersection time priority capacity of the downstream intersection of each road segment. The comprehensive priority passage potential index is directly incorporated into the basic road segment comprehensive impedance to form the priority potential modified road segment comprehensive impedance. S3. Use the comprehensive impedance of the priority potential modified road segment as the path search impedance, and use the K-shortest path algorithm to generate a set of candidate paths for emergency vehicles. S4. Based on path security constraints and path reliability constraints, the candidate path set is filtered to determine the optimal execution path and alternative paths at the current moment. S5. During the operation of emergency vehicles, continuously monitor the road network status information in the area associated with the current execution path. When the change in road network status information reaches the preset trigger condition, freeze the prefix of the executed path and use the current position of the emergency vehicle as a new starting point to perform rolling replanning of the suffix of the unexecuted path. S6. Compare the updated path obtained from the rolling replanning with the current execution path. When the overall impedance improvement of the updated path relative to the current execution path reaches the preset benefit threshold, and the path deviation of the updated path relative to the current execution path does not exceed the preset deviation threshold, replace the current execution path with the updated path; otherwise, keep the current execution path unchanged.

2. The emergency vehicle optimal route planning method considering priority potential according to claim 1, characterized in that: The expression for the combined impedance of the priority potential modified road segment is as follows: ； In the formula: For road section At any moment Priority potential for correcting the overall impedance of the road segment; For road section At any moment The basic road segment comprehensive impedance is used to characterize the basic passage cost of an emergency vehicle passing through the road segment at the current moment; For the node Pointing to node directional road sections; and These are adjacent nodes in the urban road network. For emergency vehicles to enter the road section The moment; The priority potential correction coefficient satisfies... ; For the road section The relevant comprehensive priority passage potential index, and ; Among them, the comprehensive impedance of the basic road section The expression is as follows: ； In the formula: For road section Length; For road section At any moment Queue length; For road section At any moment The traffic volume index is the number of vehicles passing through the detection section of the road segment per unit time. Traffic volume impact adjustment coefficient, which is a pre-calibrated constant; For road section At any moment The average operating speed; To avoid extremely small positive numbers with a denominator of zero.

3. The emergency vehicle optimal route planning method considering priority potential according to claim 2, characterized in that: The comprehensive priority passage potential index It is determined by both the road segment spatial priority capacity and the downstream intersection time priority capacity, and its expression is as follows: ； In the formula: For road section At any moment Priority capacity for road segment space; For downstream nodes At the intersection at time Intersection time priority capability; This is a balance coefficient between road segment space priority capacity and intersection time priority capacity, satisfying... ; The road segment space priority capability The expression is as follows: ； in, ； ； In the formula: For road section Whether a binary variable possesses the basic conditions for spatial priority; For road section The identifier variable indicates whether the facility has space priority control or collaborative control facilities; if it does, the value is 1, otherwise it is 0. For road section The number of lanes; For road section At any moment Spatial priority potential; To determine the maximum number of lanes on road sections within the study area; The normalized upper bound for the queue length of road segments within the research area is specifically the maximum observed value or preset upper limit value of the queue length of road segments within the statistical period. For road section Speed ​​limit; In the formula, The proportion of remaining lane resources on a road segment that can be used for space-priority organization; Characterize the inhibitory effect of queue length on spatial priority potential; Indicates the current smoothness of operation; The time priority capability of the intersection The expression is as follows: ； in, ； ； In the formula: Intersection Whether a binary variable meets the basic condition of time priority; For nodes Whether it is an identifier variable for a signal-controlled intersection; if yes, set to 1; otherwise, set to 0. Intersection The variable indicates whether signal priority or vehicle-road cooperative control facilities are available; if so, the value is 1, otherwise it is 0. Intersection At any moment Time-priority potential; Intersection Emergency vehicle approach direction approach lane at time Queue length; This is the normalized upper bound for the queue length at the intersection entrance lanes; For emergency vehicles approaching from the corresponding approach lane or adjacent approach section at the designated time. The average operating speed; To correspond to the speed limit of the adjacent road section; superscript This indicates the traffic volume of the approach lane or adjacent road segment in the direction that an emergency vehicle is approaching the intersection. In the formula, Characterize the inhibitory effect of entrance lane queue length on time priority potential; Characterize the impact of the operating status of the approaching road segment on time priority potential.

4. The emergency vehicle optimal route planning method considering priority potential according to claim 1, characterized in that: The path safety constraints employ a product-type risk amplification method to construct a dynamic risk index for road segments, and calculate the cumulative risk index for the path based on the dynamic risk index for road segments, as expressed below: ； ； ； In the formula: For road section At any moment The dynamic risk index; For road section The normalized value of historical accident risk; For road section At any moment Normalized values ​​of risks associated with abnormal construction, closure, or traffic conditions; For road section At any moment The real-time congestion risk normalized value; For road section At any moment The real-time volatility risk normalized value; This is a candidate path from the starting point to the target point; Emergency vehicle access routes Upper section The moment; For path The cumulative risk index; The threshold for the path risk index; in: The historical accident risk normalization value The frequency of historical traffic accidents on the road section was obtained by minimum-maximum normalization. The normalized value of the risk of abnormal construction, closure or access status. It is obtained by mapping or normalizing the road section's construction status, closure status, traffic control status, or other abnormal traffic events. The real-time congestion risk normalization value The real-time fluctuation risk normalized value is obtained by normalizing one or more of the following: road segment congestion delay index, speed reduction rate, or traffic efficiency reduction rate; The expression is as follows: ； In the formula, For the update cycle.

5. The emergency vehicle optimal route planning method considering priority potential according to claim 1, characterized in that: The path reliability constraint is constructed using a combination of expected arrival time and time buffer, and its expression is as follows: ； In the formula: For emergency vehicles entering the section of road The moment The estimated travel time for this section of the road; For path The time buffer term is used to characterize the uncertainty redundancy of the path travel time, and it is determined based on at least one of the following factors: total path length, historical travel time fluctuation level of the path, and number of critical nodes passed through the path. The maximum acceptable arrival time threshold for emergency vehicles; The path time buffer It can be represented as: ； In the formula: For path The total length; For path Number of key nodes passed through; and This is the pre-calibrated buffer adjustment coefficient.

6. The emergency vehicle optimal route planning method considering priority potential according to claim 1, characterized in that: The rolling replanning is performed by freezing the prefix and optimizing the suffix, and its expression is as follows: ； In the formula: For a moment The update execution path; Deadline Executed or locked path prefixes; For a moment Path suffix obtained through rolling optimization; This indicates a path concatenation operation; The triggering condition for the rolling replanning is determined by the change in the status of the comprehensive road network information within the area associated with the current execution path, and its expression is as follows: ； In the formula: The current execution path and its adjacent areas of influence Changes in the overall status of the road network within the area; The threshold for triggering replanning; It is a state vector; It is the difference between the state vectors at two different time points; Let be the norm of the state vector difference; The state vector includes one or more of the following: queue length, average operating speed, traffic volume, construction closure status, and route risk status. After triggering a rolling replanning, the path suffix Determine as follows: ； In the formula: This is the node corresponding to the current location of the emergency vehicle; For the target node; For a moment The set of remaining feasible nodes; To start from the current node To the target node The set of feasible suffix paths; To predict the window length; For path In the prediction window The average composite impedance within; Wherein, the average composite impedance It can be represented as: ； In the formula, For path At the predicted time The overall impedance is as follows.

7. The emergency vehicle optimal route planning method considering priority potential according to claim 6, characterized in that: The updated path and the current execution path satisfy the following benefit-deviation dual threshold switching condition: ； and ； in, ； In the formula: The current execution path The overall impedance; To update the path The overall impedance; The minimum revenue threshold for path switching; This is the length-weighted path deviation rate between the current execution path and the updated path. For path The set of edges; This is a symmetric difference operation between two sets. For the edge The length of the corresponding road segment; The maximum allowable deviation threshold for path switching; When both the above-mentioned revenue threshold and deviation threshold conditions are met, the current execution path is replaced with the updated path; otherwise, the current execution path remains unchanged.

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