A highway construction zone step-by-step speed limit grading method based on speed reduction

Abstract

The application discloses a kind of based on the speed reduction of highway construction zone step-by-step speed limit classification method, first determine the organization form of construction zone, utilize unmanned aerial vehicle to collect the traffic flow data of each control section of construction zone;Second, according to the visual recognition operation characteristics of driver to speed limit sign, set the length of single speed limit control section;Then, the simulation software is developed again, the continuous speed limit control section and the continuous control period speed reduction experiment are designed, the conflict rate on experimental section is recorded and calculated to the driving track of vehicle under speed limit, determine the speed safety reduction of construction zone according to the relationship between speed reduction and conflict rate;Finally, the construction area is step-by-step dynamic speed limit classification.The application can provide technical support for highway construction zone traffic control scheme, rely on variable speed control system, improve the traffic operation safety and efficiency of highway construction zone.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of expressway traffic control. BACKGROUND

[0002] The expressway network is a basic public facility, which plays a supporting and guiding role in promoting regional social and economic development. The early built expressways are gradually entering the maintenance and repair stage, and the construction area becomes an important part of the expressway system. As a typical bottleneck section of the expressway, the expressway construction area causes the reduction of available lanes due to the occupation of part of the lanes for maintenance and construction, which easily leads to congestion and queuing, and the running vehicles have to frequently change lanes and merge upstream of the bottleneck section, which adversely affects the safe operation and traffic efficiency of the section.

[0003] At present, the traffic control of the expressway construction area is based on the Highway Maintenance Safety Operation Regulations (JTGH30-2015), and static fixed speed limit signs are set in the warning area to guide vehicles to gradually reduce the speed according to the speed limit. The number and speed limit value of the speed limit signs in the construction area are set according to the default value, the number of speed limits is unreasonable, and the speed limit value cannot be adjusted in real time according to the traffic flow state of the section, so the speed limit control effect has certain limitations. With the in-depth research and application of variable speed limit technology, it is possible to set multiple variable speed limit signs in the control section to control the speed of the running vehicles.

[0004] The number of speed limit classification is closely related to the traffic safety of the construction area. The fewer the number of speed limit classification, the fewer the number of variable speed limit signs, the greater the gap between the vehicle speed and the speed limit value, the sharp speed reduction, and the higher the conflict rate caused by the high dispersion degree of the vehicle speed in the construction section. The more the number of speed limit classification, the more the number of variable speed limit signs needed to be set, and the more gentle the speed reduction of the running vehicles. However, too many speed limit classifications will cause the driver to frequently reduce the speed, which may cause the driver to feel urgent and make mistakes, and also cause the driver to feel annoyed and rebellious, and the speed limit compliance rate may be reduced. Therefore, formulating a scientific and reasonable number of speed limit classification is the key to ensuring the speed limit control effect of the construction area. SUMMARY

[0005] The purpose of the application is to solve the problems existing in the prior art, and a speed limit classification method for expressway construction area based on speed reduction is provided.

[0006] Technical scheme: The application provides a speed limit classification method for expressway construction area based on speed reduction, which specifically includes the following steps:

[0007] Step 1: collecting traffic flow data of the expressway construction area;

[0008] Step 2: dividing the upstream road section of the highway construction area into a warning zone and an upstream excessive section, the warning zone including a warning zone upstream, a warning zone middle section, a warning zone end; the upstream excessive section being a road narrowing section between the warning zone end and the construction area;

[0009] Step 3: setting the length L of a single speed limit control section;

[0010] Step 4: selecting a road section with a length of 2L at the end of the warning zone and the upstream excessive section as an experimental road section; and dividing the road section with a length of 2L at the end of the warning zone into two speed limit control sections with a length of L; the two speed limit control sections being continuous speed limit control sections;

[0011] Step 5: using simulation software, setting a plurality of simulation cycles, fixing the speed limit values of the two continuous speed limit control sections in a simulation cycle, obtaining the speed reduction amplitudes between the two continuous speed limit control sections, and obtaining the conflict rates corresponding to each speed reduction amplitude;

[0012] Step 6: setting a conflict rate threshold S, selecting the conflict rate closest to the conflict rate threshold S, and taking the speed reduction amplitude corresponding to the conflict rate as the speed safety reduction amplitude F of the continuous speed limit control section;

[0013] Step 7: setting a continuous speed limit control cycle in the simulation software, dynamically changing the speed limit values of the two speed limit control sections in the continuous speed limit control cycle, obtaining the speed reduction amplitudes at each change, and calculating the conflict rates corresponding to each speed reduction amplitude;

[0014] Step 8: setting a conflict rate threshold S1; in step 7, selecting the conflict rate closest to the conflict rate threshold S1, and taking the speed reduction amplitude corresponding to the conflict rate as the speed safety reduction amplitude F1 of the continuous speed limit control cycle;

[0015] Step 9: according to the length L of a single speed limit control section, the speed safety reduction amplitude of a continuous speed limit control section, and the speed safety reduction amplitude of a continuous speed limit control cycle determined in step 3, performing dynamic speed limit grading on the construction area in stages.

[0016] Further, the step 3 is specifically:

[0017] The single speed limit control section includes a vehicle travel distance s0 from when a driver discovers a roadside speed limit sign to when the driver starts to recognize the speed limit sign, a vehicle travel distance s1 during the recognition process, a vehicle travel distance s2 from when the recognition is completed to when a speed reduction measure is taken, a vehicle travel distance s3 from when the driver takes the speed reduction measure to when the vehicle speed is reduced to the speed limit requirement, and a vehicle travel distance s4 from when the vehicle speed is reduced to the speed limit value to when the vehicle enters the next speed limit control section after stable driving for x seconds:

[0018] L=s0+s1+s2+s3+s4

[0019]

[0020]

[0021]

[0022]

[0023] s4 = x · v l

[0024] Wherein, v1 represents the initial speed when the driver discovers and starts to recognize the speed limit sign, t0 represents the interval time from discovery to start of recognition, t1 represents the recognition understanding time, t2 represents the reaction time from completing recognition to taking deceleration operation, v l represents the speed limit value, g represents the gravity acceleration, represents the road friction coefficient, b represents the road longitudinal slope.

[0025] Further, the conflict rate in step 5 or step 8 is calculated by using the following formula:

[0026] R c = N c / L

[0027] Wherein, N c is the sum of rear-end conflict and lateral conflict times;

[0028] The distance collision time TTC1t representing traffic safety is used as an evaluation index when calculating the rear-end conflict times, and the potential collision time TTC2t under lateral conflict is used as an evaluation index when calculating the lateral conflict times;

[0029]

[0030]

[0031] Wherein, Δd represents the distance between the head of the rear vehicle B and the tail of the front vehicle A at t time, v A (t) and v B (t) respectively represent the speed of the rear vehicle B and the front vehicle A at t time; d A (t) and d B (t) respectively represent the distance between the head of the vehicles A and B and the potential collision point at t time during the lane changing operation, L A and L B respectively represent the body length of the vehicles A and B.

[0032] Further, the step 9 is specifically:

[0033] Step 9.1: If the absolute value of the difference between the average speed v i of the upstream road section of the highway construction area in the initial speed limit control period and the optimal speed limit value v vsl1 of the initial speed limit section 1 on the highway is less than or equal to the speed safety reduction F of the continuous speed limit control section, the first-level speed limit is reset in the warning area, and step 9.3 is turned to, otherwise step 9.2 is turned to; the resetting of the first-level speed limit is specifically: the first L meters of the upstream excessive section are taken as the speed limit section 1, and a dynamic speed limit sign is set at the first L meters of the upstream excessive section, with the speed limit value being v vsl1 ;

[0034] Step 9.2: A speed limit section 2 is set at the first L meters of the speed limit section 1, the optimal limit value v vsl2 of the speed limit section 2 is calculated, and the speed reduction between v vsl2 and v vsl1 is less than or equal to F; if the absolute value of the difference between v i and v vsl2 is less than or equal to F, the speed limit section 2 is retained, and dynamic speed limit signs are set at the speed limit section 1 and the speed limit section 2, with the speed limit values being v vsl1 and v vsl2 ; if the absolute value of the difference between v i and v vsl2 is greater than F, a new speed limit section is set at the first L meters of the speed limit section 2, the optimal speed limit value of the new speed limit section is compared with v i , step 9.2 is repeated until the speed limit section is set, and step 9.3 is turned to;

[0035] Step 9.3: If the number of speed limit sections in the current speed limit control period is greater than 1, the optimal limit values of the speed limit sections in the next speed limit control period are optimized, the speed reduction between the adjacent two speed limit sections after the optimization is less than or equal to F, and the speed reduction between the adjacent two speed limit control periods of the same speed limit section is less than or equal to F1; if the number of speed limit sections in the current speed limit control period is equal to 1, v i is compared with the optimal limit value of the optimized speed limit section 1 according to the method of step 9.1, and it is judged whether a speed limit safety section needs to be added.

[0036] Beneficial effects: The application proposes a highway construction zone step-by-step variable speed limit grading control method based on speed safety drop experiment, takes variable speed limit control technology as support, develops secondary VISSIM simulation software and designs speed drop experiment, analyzes the relationship between continuous control section, continuous control period speed change and construction zone safety operation, determines the speed safety drop of construction zone, and determines the construction zone speed limit grading scheme according to the highest speed limit, the lowest speed limit and the length of speed limit control section and other constraints. The application can provide technical support for the traffic control scheme of highway construction zone, rely on variable speed limit control system, and improve the traffic operation safety and efficiency of highway construction zone. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The flowchart of the application;

[0038] Figure 2 The schematic diagram of construction zone control section division;

[0039] Figure 3 The schematic diagram of driver's speed limit sign visual recognition operation;

[0040] Figure 4 The schematic diagram of speed drop experiment road section;

[0041] Figure 5 The schematic diagram of rear-end and lateral collision;

[0042] Figure 6 The schematic diagram of construction zone variable speed limit control system,

[0043] Figure 7 The flowchart of construction zone speed limit grading times determination. DETAILED DESCRIPTION

[0044] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application, illustrate the preferred embodiments of the application, and assist in the explanation of the application. The schematic embodiments of the application and their descriptions are used to explain the application, and do not constitute undue limitations on the application.

[0045] As shown in Figure 1 , the embodiment provides a highway construction zone step-by-step speed limit grading method based on speed drop, which specifically includes the following steps:

[0046] Step 1: Use a drone to collect traffic flow data in the construction zone, extract vehicle driving track based on Tracker software and clean and correct the data.

[0047] Step 2: Refer to the domestic highway maintenance specification to divide each control section of the construction zone, specifically as Figure 2As shown in FIG. 4, the warning zone is divided into three control sections, i.e., an upstream section of the warning zone, a middle section of the warning zone, and an end section of the warning zone, according to the length of the driving lane of the road and the range of the UAV. The narrowed road section downstream of the warning zone is taken as an upstream transition section for convenience of collection. After the collection is completed, the speed of each control section is statistically analyzed. Since the speed of the road section gradually decreases from the upstream to the downstream of the warning zone, the 85th percentile speed of 100 km / h of the upstream of the warning zone is taken as the maximum speed limit value of the construction zone in this embodiment. Since the road capacity changes due to the lane occupation for construction in the upstream transition section, congestion and queuing occur, and the speed is low, the 15th percentile speed of 40 km / h of the upstream transition section is taken as the minimum speed limit value of the construction zone in this embodiment.

[0048] Step 3: Calculate the length of the speed limit control section according to the visual recognition operation characteristics of the driver to the speed limit sign, as shown in FIG. 5. Figure 3 According to the visual recognition operation characteristics of the driver to the speed limit sign, the minimum length of a single speed limit control section is set to the distance traveled by the vehicle from the discovery of the roadside speed limit sign to the requirement of reducing the speed to the speed limit value in this embodiment. Specifically, it includes the distance s0 traveled by the vehicle from the discovery of the roadside speed limit sign to the beginning of visual recognition of the speed limit sign, the distance s1 traveled by the vehicle during visual recognition, the distance s2 traveled by the vehicle from the completion of visual recognition to the adoption of deceleration measures, and the distance s3 traveled by the vehicle from the adoption of deceleration measures to the reduction of the speed to the requirement of the speed limit. The visual recognition operation diagram of the driver is shown in FIG. 6. Figure 3 The minimum length L of a single speed limit control section can be expressed as: min which can be expressed as:

[0049]

[0050] where v1 represents the initial speed of the driver when discovering and beginning to visually recognize the speed limit sign, t0 represents the interval time from discovery to beginning of visual recognition, t1 represents the visual recognition understanding time, t2 represents the reaction time from completion of visual recognition to adoption of deceleration operation, v l represents the speed limit value, g represents the acceleration of gravity, represents the road friction coefficient, and b represents the road longitudinal slope.

[0051] If the driver reduces the speed to the speed limit value and then enters the next speed limit control section and takes acceleration and deceleration measures according to the new speed limit value, the frequent operation in a short time easily increases the driving safety risk of the construction zone. Therefore, the safe driving distance s4 of the vehicle is set, which represents the distance traveled by the vehicle after stably driving for x seconds after the speed is reduced to the speed limit value and then enters the next speed limit control section. In this embodiment, x = 10. The length L of a single speed limit control section of the construction zone can be expressed as:

[0052] L = L min + s4 = L min + 10 · v l

[0053] The possible speed limit value changes in the construction area are calculated respectively, and the length of the single speed limit control section in the construction area is determined according to the calculation results; in this embodiment, L = 500 m.

[0054] Step 4: According to the calculation formula in step 3, the length of the speed limit control section in the construction area is determined to be 500 m. In this embodiment, the last 1000 m of the warning area and the 200 m section downstream of the warning area are selected as the vehicle speed drop experimental section when designing the experimental road section. The VISSIM simulation software is used to build the vehicle speed drop experimental section and calibrate the experimental parameters, as shown in FIG. 4. Figure 4 According to the calculation results in step 3, the 1000 m section is divided into two speed limit control sections, namely section 1 and section 2. The speed limit decision point function in the VISSIM software is used to limit the speed of the vehicle in the section, and the speed limit value change in the adjacent speed limit section is used to represent the speed change of the vehicle in the continuous speed limit section. The expected speed decision point in the simulation software is called by the MATLAB software to control the speed limit value and the speed limit period.

[0055] Step 5: Vehicle speed drop experiment in continuous speed limit section: take 3600 s as the simulation period, take the measured flow upstream of the construction area as the flow input in the experiment, set the speed limit value of the speed limit section 1 to the maximum speed limit value of the construction area 100 km / h, and set the speed limit value of the speed limit section 2 to 90 km / h, 80 km / h, … the minimum speed limit value of the construction area. With the continuous decrease of the speed limit value, the speed drop in the continuous speed limit section increases, and the change of the speed limit value in the continuous speed limit section is used to realize the speed change of the vehicle in the continuous speed limit control section.

[0056] Step 6: Vehicle speed drop experiment in continuous control period: when the dynamic speed limit control is implemented in the construction area, the variable speed limit control system calculates the optimal speed limit value of the section in the speed limit control period, and publishes the speed limit value through the variable speed limit sign. In this embodiment, 5 min is taken as the continuous speed limit control period, and in one simulation time, the speed limit value of the speed limit section 2 is designed to change dynamically with the speed limit control period, so as to realize the speed change of the vehicle in the single speed limit control section in the continuous speed limit control period. The specific experimental scheme is shown in Table 1:

[0057] Table 1

[0058]

[0059] In the experimental scheme, 0-600 s is the simulation warm-up time, and 600-900 is the first speed limit control period.

[0060] The implementation of speed limit function in VISSIM simulation software is mainly through setting desired speed decision point and setting deceleration zone, but the two ways cannot realize the dynamic change of speed limit value in the experiment of speed reduction in continuous control cycle. Therefore, in order to realize the experimental scheme in step 6, it is necessary to set the desired speed decision point in the experimental section first and then call it by using MATLAB software. The desired speed decision point preset in VISSIM is captured by "GetDesiredSpeedDecisionByNumber(i)" command to realize the goal of dynamic change of vehicle desired speed through the decision point with control cycle.

[0061] Step 7: In order to analyze the relationship between speed reduction and conflict rate, it is necessary to calculate the conflict times of the experimental section. In this embodiment, the time to collision (TTC) representing traffic safety is selected as the evaluation index. Combined with the rear-end collision and lateral collision caused by lane changing in the construction area, the potential collision point concept of post-encroachment time (PET) is introduced to improve the original TTC calculation formula, which can be specifically expressed as:

[0062]

[0063]

[0064] In the formula, TTC1(t) is the potential time to collision under rear-end collision, Δd represents the distance between the front of the following vehicle B and the rear of the leading vehicle A at time t, v A (t) and v B (t) represent the speed of the following vehicle B and the leading vehicle A at time t, respectively; TTC2(t) is the potential time to collision under lateral collision, d A (t) and d B (t) represent the distance between the front of the two vehicles A and B and the potential collision point at time t, respectively, L A and L B represent the length of the two vehicles, and the specific collision schematic diagram is shown in Figure 5 .

[0065] When A car changes lanes, there will be a potential collision point with the straight B car on the target lane. According to the time difference of A and B cars passing through the potential collision point, there will be three situations: 1. The head of B car passes through the potential collision point first, and the head of A car reaches the potential collision point earlier than the tail of B car, at this time A car will collide with B car from the rear side; 2. The head of A car passes through the potential collision point first, and the head of B car reaches the potential collision point earlier than the tail of A car, at this time B car will collide with A car from the rear side; 3. The tail of A and B cars passes through the potential collision point earlier than the head of the rear car, at this time the two cars will not produce lateral collision due to lane changing. Based on the above analysis, the improved TTC calculation formula can be used to calculate the derived vehicle trajectory data.

[0066] Step 8: Calculate the TTC value of the vehicle in the simulation time using the formula in step 7, and define the TTC value less than 1.5s as a conflict. The number of conflicts in the experiments of step 5 and step 6 is determined by analyzing the relationship between the speed drop and the conflict rate R c , to determine the critical speed limit value when the traffic safety risk in the section suddenly changes and thus determine the speed safety drop in the construction zone. c Can be expressed as:

[0067] R c = N c / L

[0068] In the formula, N c is the sum of the number of rear-end conflicts and lateral conflicts, and L is the length of the test section;

[0069] is the collision distance time of the vehicle in the simulation time calculated by the formula in step 7, which needs to record the horizontal and vertical coordinate positions of the vehicle at each simulation step and the current time through the VISSIM vehicle recording function. After all simulation experiments are completed, the vehicle trajectory is derived for calculation. When calculating the lateral conflict metric TTC2(t), different collision situations of A and B cars need to be analyzed, as shown in Figure 4 .

[0070] The calculation results of R c in step 5 and step 6 are shown in Table 2 and Table 3 respectively:

[0071] Table 2

[0072]

[0073] Table 3

[0074]

[0075] The calculation result shows that the conflict rate in the road section is proportional to the sharp degree of the speed reduction, and the greater the speed reduction, the higher the conflict rate in the test road section. A conflict rate threshold S is set, the conflict rate closest to the conflict rate threshold S is selected in the experiment of step 5, and the speed reduction corresponding to the conflict rate is taken as the speed safety reduction F of the continuous speed limit control section; a conflict rate threshold S1 is set; in the experiment of step 6, the conflict rate closest to the conflict rate threshold S1 is selected, and the speed reduction corresponding to the conflict rate is taken as the speed safety reduction F1 of the continuous speed limit control period; in this embodiment, F and F1 are both 20km / h; it can be seen from Tables 2 and 3 that when the speed reduction exceeds 20km / h, the number of conflicts in the road section begins to increase greatly, and the conflict rate increases significantly, which brings challenges to the safe driving in the construction area.

[0076] Based on the optimal speed limit value of the bottleneck road section in the construction area calculated by the construction area variable speed limit control system, a step-by-step variable speed limit control scheme is determined, and the construction area variable speed limit control system is as shown in Figure 6 .

[0077] In the variable speed limit control system, when a vehicle enters the highway maintenance construction road section, the road detector such as the loop coil collects the road traffic flow information in real time and transmits the data to the control center, and when it is detected that the road traffic flow density exceeds the congestion critical density p C , the speed limit control is started. The control center determines the optimal speed limit value of the current road section according to the speed limit control model, and publishes the corresponding speed limit information to the variable speed limit signs in the warning area road section, so as to realize the speed limit control.

[0078] As shown in Figure 7 , it is assumed that the average speed of the upstream road section when the speed limit control is started is v i , and the optimal speed limit value calculated by the control center is v vsl1 (initially the road section is the initial speed limit section 1). If the absolute value of the difference between the speed v i and the speed limit value v vsl1 is less than the speed safety reduction (|v i -v vsl1 |≤20km / h), then only one level of speed limit needs to be set in the warning area road section, that is, a dynamic speed limit sign can be set at a position ≥500m upstream of the upstream transition zone, and the speed limit section 1 is from the speed limit sign position to the start point of the upstream transition zone, and the speed limit value is v vsl1 . If the absolute value of the difference between the speed v i and the speed limit value v vsl1 exceeds the speed safety reduction (|v i -v vsl1|>20km / h), then speed limit section 2 needs to be set, and the optimal speed limit value v vsl2 (v vsl2 The difference between v vsl1 and the speed limit value v i is 10km / h or 20km / h, re-determine the vehicle speed v vsl2 and the speed limit value v vsl2 ; if the absolute value of the speed difference meets the requirements, set a secondary speed limit in the warning zone section, and at this time, dynamic speed limit signs need to be set in two speed limit control sections, with speed limit values of v vsl1 and v i ; if the absolute value of the difference between the vehicle speed v vsl2 and the speed limit value v vsl3 still exceeds the speed safety reduction, speed limit section 3 needs to be set and the optimal speed limit value v vsl3 in the section is continuously optimized. Repeat the above judgment, if the speed safety reduction requirement is met, set a tertiary speed limit in the warning zone section, with speed limit values of v vsl2 , v vsl1 , and v i in the three speed limit control sections, respectively; if the requirement is not met, continue to add speed limit control sections and optimize the optimal speed limit value in the section, and so on, until the final construction zone variable speed limit grading control scheme is determined.

[0079] If the number of speed limit sections in the current speed limit control period is greater than 1, the optimal limit value of each speed limit section in the next speed limit control period is optimized, and the speed reduction between the adjacent two speed limit sections is less than or equal to F, and the speed reduction between the adjacent two speed limit control periods of the same speed limit section is less than or equal to F1; if the number of speed limit sections in the current speed limit control period is equal to 1, compare v i with the optimal limit value of the optimized speed limit section 1 to determine whether a speed limit safety section needs to be added.

[0080] It should be noted that during the speed limit control of the construction zone section, the speed limit value in the continuous control period also needs to meet the speed safety reduction requirement to reduce the vehicle conflict rate in the speed limit section. According to relevant specifications, the speed limit control of the construction zone should be completed in the warning zone, so the total length of the speed limit control section should be less than the length of the warning zone, i.e.

[0081] N≤S / L

[0082] In the formula, N is the number of speed limit gradings, and S is the length of the warning zone.

[0083] It should also be noted that various specific technical features described in the above specific embodiments can be combined in any suitable manner, without contradiction. In order to avoid unnecessary repetition, the present application will not describe various possible combinations again.

Claims

1. A method for grading speed limits in highway construction zones based on vehicle speed reduction, characterized in that: The specific steps include: Step 1: Collect traffic flow data in the highway construction area; Step 2: Divide the upstream section of the highway construction area into a warning area and an upstream transition section. The warning area includes the upstream section of the warning area, the middle section of the warning area, and the end of the warning area. The upstream transition section is the narrowing section of the road between the end of the warning area and the construction area. Step 3: Set the length L of a single speed limit control section; Step 4: Select the section with a length of 2L at the end of the warning zone and the upstream transition section as the experimental sections; divide the section with a length of 2L at the end of the warning zone into two speed limit control sections with a length of L; the two speed limit control sections are continuous speed limit control sections; Step 5: Using simulation software, set several simulation cycles. Within one simulation cycle, set the speed limit values ​​of two consecutive speed limit control sections to a fixed value. Obtain the speed reduction between the two consecutive speed limit control sections, and obtain the conflict rate corresponding to each speed reduction. Step 6: Set the conflict rate threshold S, select the conflict rate closest to the conflict rate threshold S, and use the speed reduction corresponding to the conflict rate as the speed safety reduction F for the continuous speed limit control section; Step 7: Set a continuous speed limit control cycle in the simulation software. Dynamically change the speed limits of the two speed limit control sections during the continuous speed limit control cycle, obtain the speed reduction during each change, and calculate the conflict rate corresponding to each speed reduction. Step 8: Set the conflict rate threshold S1; in step 7, select the conflict rate closest to the conflict rate threshold S1, and use the speed reduction corresponding to the conflict rate as the speed safety reduction F1 of the continuous speed limit control cycle; Step 9: Determine the length L of a single speed limit control section, the safe speed reduction margin for continuous speed limit control sections, and the safe speed reduction margin for continuous speed limit control cycles based on step 3, and implement dynamic speed limit classification for the construction area. The step 3 is specifically as follows: The single speed limit control section includes the vehicle's travel distance s0 from the time the driver discovers the roadside speed limit sign to the time the driver begins to visually recognize the speed limit sign, the vehicle's travel distance s1 during the visual recognition process, the vehicle's travel distance s2 from the time the visual recognition is completed to the time the deceleration measures are taken, the vehicle's travel distance s3 from the time the driver takes the deceleration measures to the time the speed is reduced to the speed limit, and the vehicle's travel distance s4 from the time the speed is reduced to the speed limit and then the vehicle enters the next speed limit control section after driving steadily for x seconds. L=s0+s1+s2+s3+s4 s4=x v l Among them, v1 represents the initial speed when the driver discovers and starts to visually recognize the speed limit sign, t0 represents the interval time from the driver discovering to starting to visually recognize, t1 represents the visual understanding time, t2 represents the reaction time from completing visual recognition to taking deceleration action, v l Indicates the speed limit, g indicates the acceleration due to gravity, represents the road friction coefficient, and b represents the road longitudinal slope.

2. The method for grading speed limits in highway construction zones based on speed reduction according to claim 1, characterized in that: The collision rate in step 5 or step 8 is calculated using the following formula: R c =N c / L Among them, N c is the sum of the number of rear-end collisions and side collisions; When calculating the number of rear-end collisions, the distance-to-collision time TTC1(t), which represents traffic safety, is used as the evaluation indicator. When calculating the number of lateral collisions, the potential collision time under lateral collisions TTC2(t) is used as the evaluation indicator. Among them, Δd represents the distance between the front of the rear vehicle B and the rear of the front vehicle A at time t, v A (t) and v B (t) represents the speed of the rear vehicle B and the front vehicle A at time t; d A (t) and d B (t) represents the distance between the front of vehicle A and vehicle B and the potential collision point at time t during lane change operation, L A With L B Represent the body lengths of vehicles A and B respectively.

3. The method for grading speed limits in highway construction zones based on speed reduction according to claim 1, characterized in that: The step 9 is specifically as follows: Step 9.1: If the average vehicle speed vi of the upstream section of the highway construction area during the initial speed limit control period is equal to the optimal speed limit value v of the initial speed limit section 1 on the highway, vsl1 If the absolute value of the difference between the two is less than or equal to the speed safety reduction margin F of the continuous speed limit control section, reset the first-level speed limit in the warning area and go to step 9.3; otherwise, go to step 9.2; reset the first-level speed limit as follows: set the first L meters of the upstream transition section as speed limit section 1, and set a dynamic speed limit sign at the first L meters of the upstream transition section, with the speed limit value v vsl1 ; Step 9.2: Set speed limit section 2 L meters before speed limit section 1 and calculate the optimal limit value v for speed limit section 2. vsl2 , and v vsl2 and v vsl1 The speed reduction between the two is less than or equal to F; if v i With v vsl2 If the absolute value of the difference between them is less than or equal to F, then the speed limit section 2 is retained and dynamic speed limit signs are set in speed limit sections 1 and 2 respectively, with the speed limit value of v vsl1 and v vsl2 If v i With v vsl2 If the absolute value of the difference between them is greater than F, a new speed limit section is set L meters before speed limit section 2, and the optimal speed limit value of the new speed limit section is compared with v i Compare and repeat step 9.2 until the speed limit section is set, then go to step 9.3; Step 9.3: If the number of speed limit sections in the current speed limit control cycle is greater than 1, optimize the optimal limit value of each speed limit section in the next speed limit control cycle. The speed reduction between two adjacent speed limit sections after optimization is less than or equal to F, and the speed reduction between two adjacent speed limit control cycles in the same speed limit section is less than or equal to F1. If the number of speed limit sections in the current speed limit control cycle is equal to 1, then follow the method in step 9.1 to set v i Compare this with the optimal limit of the optimized speed limit section 1 to determine whether a speed limit safety section needs to be added.

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