A roundabout signal timing method based on shifted left turn and secondary stop

Abstract

The present invention relates to the technical field of transportation planning, and specifically to a roundabout signal timing method based on shifted left turn and secondary parking. The timing method includes: step 1, investigating the geometric conditions and traffic volume of the roundabout; determining the layout of the shifted left turn lane; setting traffic lights, setting corresponding traffic signs and markings; step 2, signal light phase design, using two-phase traffic rules; step 3, under the condition of no traffic conflict and the maximum traffic capacity of the roundabout as the goal, the passage time of straight and right turning vehicles is determined according to the passage time of the secondary left turning vehicle, and the roundabout signal timing method is determined, which specifically includes: left shifting vehicle entering the ring timing, left turning out of the ring shifting vehicle timing, straight vehicle timing and pedestrian crossing timing. By adopting the above scheme, the present invention solves the problems of poor traffic capacity of roundabouts, serious traffic conflicts in roundabouts, and increased average vehicle delays due to long phase cycle duration.

Description

Technical Field

[0001] The invention relates to the technical field of transportation planning, and in particular to a roundabout signal timing method based on shifted left turn and secondary parking. Background Art

[0002] Roundabouts (also called roundabouts) are usually characterized by a circular road around a central island, with left-turn and through-traffic flows going counterclockwise around the island until they exit the ring and complete the turn. Under low and medium traffic conditions, roundabouts are usually able to adapt and traffic flow is relatively smooth. However, with the growth of motor vehicle ownership and the rapid increase in road traffic volume, roundabouts are likely to become traffic bottlenecks due to their inherent limitations.

[0003] At present, in order to ensure the traffic flow of roundabouts, traffic lights are often installed at the entrance of roundabouts, and traffic control methods are used to allocate road rights at intersections. This method does not separate the conflict points on the roundabout, so that even with signal control, there is still a weaving phenomenon, resulting in unstable traffic flow. If drivers still pass through at will at this time, it will cause unstable traffic flow and increase the congestion of the roundabout. To solve the above problems, it is necessary to add signals to the roundabout to eliminate the conflict points between left-turning and straight-going traffic and further allocate road rights. However, this will increase the signal phases and the signal cycle time, resulting in an increase in average vehicle delays.

[0004] In large roundabouts, left-turning traffic has the longest trajectory and causes the most conflict points, so left-turning traffic should be the first focus when alleviating roundabout congestion. Faced with intersections with heavy traffic loads and a certain amount of road expansion space, the introduction of the concept of shifted left turns provides a possible improvement solution for such intersections and the passage of left-turning traffic.

[0005] Roundabouts are in urgent need of a timing method that can not only give full play to the advantages of the shifted left-turn traffic organization method, alleviate traffic conflicts at roundabouts, and improve the traffic capacity of roundabouts; at the same time, the number of signal phases is not large, which can enable traffic to pass continuously in the roundabout, reduce the average vehicle delay, and improve the space utilization rate of the roundabout. Summary of the invention

[0006] In order to solve the problems of poor roundabout capacity, traffic conflicts in roundabouts, and increased average vehicle delays due to long phase cycle duration, the present invention provides a roundabout signal timing method based on shifted left turns and secondary stops, including the setting of shifted left turn areas and lengths, and a timing scheme under this method.

[0007] To achieve the above object, the present invention adopts the following technical solution:

[0008] A roundabout signal timing method based on shifted left turn and secondary parking is performed according to the following steps:

[0009] Step 1: Investigate the geometric conditions and traffic volume of the roundabout; determine the layout of the shifted left-turn lane of the roundabout; set up traffic lights at the roundabout, and set up corresponding traffic signs and markings;

[0010] Step 2: Design the phase of the signal lights to determine whether the roundabout adopts a two-phase traffic rule;

[0011] Step 3: With no traffic conflict as a condition and the maximum traffic capacity of the roundabout as a goal, the traffic time of straight and right-turn vehicles is determined according to the traffic time of the second left-turn vehicle, and the roundabout signal timing method is determined, which specifically includes:

[0012] Step 3-1: Timing of vehicles entering the ring for left shifting, determine the release method and release time of vehicles entering the ring for left shifting:

[0013] The release time of vehicles entering the left-turn roundabout is determined by the maximum number of parked vehicles in the waiting area of ​​the left-turn roundabout, the length of the waiting area of ​​the left-turn roundabout, the average headway distance when the vehicles stop, the average time for a single vehicle to pass the stop line and the start-up loss time;

[0014] Step 3-2: Timing of vehicles shifting out of the left turn ring, determine the release method and release time of vehicles shifting out of the left turn ring:

[0015] The release time of the displaced vehicle turning out of the left turn ring is determined by the length of the left turn ring area, the length of the waiting area of ​​the left turn ring, the length of the displaced left turn area, the average driving speed of the vehicle under the condition of stationary starting, and the starting loss time;

[0016] Step 3-3: Timing of through vehicles: Determine the release method and time of through vehicles:

[0017] The release time for straight-going vehicles is determined based on the release time for vehicles entering the ring and turning left, the release time for vehicles leaving the ring, the advance start time, and the green light interval time for straight-going vehicles.

[0018] Step 3-4: Timing of pedestrian crossings: determine the method and time of releasing pedestrians:

[0019] The time to release pedestrians crossing the street is determined by the duration of a single phase;

[0020] Step 3-5: The phase in the other direction is determined in the same manner as in steps 3-1 to 3-4.

[0021] Furthermore, the timing method is applicable to the following traffic organization mode: the passage order of left-turning vehicles is to first shift left, then turn left directly to the left-turn roundabout waiting area to stop and wait, then exit the roundabout, and then shift to the normal lane through the shift left-turn area.

[0022] Furthermore, in step 1, the investigation of the geometric conditions and traffic volume of the roundabout specifically includes the following steps:

[0023] Step 1-1: Investigate the geometric conditions of the roundabout:

[0024] Measure the road width of each entrance road of the roundabout, the width of the ring road, the width of the sidewalk, the length of the waiting area of ​​the left-turn ring road, the length of the tail-clearing area of ​​the straight traffic flow, the length of the shift section, the length of the left-turn entry ring area and the length of the left-turn exit ring area;

[0025] Step 1-2: Survey traffic volume at the roundabout:

[0026] Investigate the flow rate and direction of entrances in all directions, the pedestrian, non-motor vehicle and motor vehicle traffic volume and their composition at each entrance, and the cross-sectional flow rate of the roundabout; investigate the average driving speed of vehicles under stationary starting conditions, investigate the average driving speed of vehicles when they are running continuously; investigate the average headway distance when vehicles are stopped; investigate the average time it takes for a single vehicle to pass the stop line.

[0027] Further, in step 1, determining the layout of the shifted left-turn lane at the roundabout specifically includes the following steps:

[0028] Step 1-3, determine the number of shifted left-turn lanes at the roundabout, the number of lanes in the left-turn connection area of ​​the entrance road, the position of the shifted left-turn area and the length of the shifted section;

[0029] Steps 1-4: Set the number of lanes, start and end positions, and secondary stop line position of the left-turn lane waiting area of ​​the roundabout according to the number and position of the shifted left-turn lanes.

[0030] Furthermore, the setting of traffic lights at the roundabout is specifically as follows: Z1, Z2, Z3, and Z4 are set as signal lights for vehicles turning left into the roundabout in the four directions of south, east, north, and west; H1, H2, H3, and H4 are set as secondary stop line signal lights in the four directions of south, east, north, and west, that is, signal lights for vehicles turning left out of the roundabout; S1, S2, S3, and S4 are set as signal lights for vehicles going straight in the four directions of south, east, north, and west; and R1, R2, R3, and R4 are set as signal lights for pedestrians crossing the street in the four directions of south, east, north, and west.

[0031] Furthermore, in step 2, the determination of the roundabout using the two-phase traffic rule is specifically as follows:

[0032] In the first phase, the north-south entrance lane phase is the key phase, and the north-south left turn secondary stop phase is divided into the first half of the shifted left turn lane phase and the second half of the left turn ring road waiting phase. The two phases share the north-south key phase duration;

[0033] In the second phase, the east-west entrance lane phase is the key phase, and the east-west left turn is a second stop. The phase is divided into the first half of the shifted left turn lane phase and the second half of the left turn ring road waiting zone phase. The two phases share the length of the east-west key phase.

[0034] Furthermore, in step 3-1, the release time of the left-turning vehicle is determined by the maximum number of parked vehicles in the waiting area of ​​the left-turn roundabout, the length of the waiting area of ​​the left-turn roundabout, the average headway distance when the vehicles stop, the average time for a single vehicle to pass the stop line, and the start-up loss time, specifically:

[0035] The maximum number of parked vehicles N in the waiting area of ​​the left-turn roundabout in the i-th direction i Equal to the length of the waiting area for the left turn in this direction, L i Divide by the average headway S when the vehicles are stopped, see formula (1):

[0036] N i =L i / S (1)

[0037] Green light time for vehicles entering the ring at the left transfer position in the i-th direction Equal to the maximum number of parked vehicles N in the waiting area of ​​the left-turn roundabout in this direction i Multiply it by the average time t for a single vehicle to pass the stop line, see formula (2):

[0038]

[0039] The green light time for vehicles entering the ring in the left shift phase is equal to the smaller value of the green light time for vehicles entering the ring in the left shift phase in the two opposite directions. Add the startup loss time l, which is determined by investigation, as shown in formula (3) (4):

[0040]

[0041]

[0042] Further, in step 3-2, the release time of the displaced vehicle turning out of the left turn ring is determined by the length of the left turn ring area, the length of the waiting area of ​​the left turn ring road, the length of the displaced left turn area, the average driving speed of the vehicle under the condition of stationary starting, and the starting loss time, specifically:

[0043] Turn left out of the ring and enter the i direction green light early start time t f,i , calculated as the length of the left turn loop area of ​​the i entrance road X c,i The ratio of the average speed v1 of the vehicle under static starting conditions is shown in formula (5):

[0044] t f,i =X c,i / v1 (5)

[0045] Take the opposite direction release, the phase left turn ring shift vehicle green light early start time t o,1 ,t o,2 Choose two relative directions t f,i The smaller value ensures that when the left-turning out-of-ring shifting vehicle arrives at the shifted left-turn area, the left-turning in-ring shifting vehicle has been released; the green light advance start time of the left-turning out-of-ring shifting vehicle in a single phase is equal to the smaller advance start time min (t f,i ) plus the starting loss time l, the two phase advance starting time is shown in formulas (6) and (7):

[0046] t o,1 = l + min (t f,i ) (i is the first phase release direction) (6)

[0047] t o,2 = l + min (t f,i ) (i is the second phase release direction) (7)

[0048] The total release time of a phase must ensure that the last left-turning vehicle in both directions passes through the shifted left-turn area. The calculation method is: calculate the ratio of the sum of the length of the left-turning loop area, the length of the waiting area of ​​the left-turning loop, and the length of the shifted left-turn area in the two relative directions to the average driving speed v1 of the vehicle under static starting conditions. The larger value between the two relative directions is selected as the ratio, and then the start loss time is added to it, which is taken as the total release time of the left-turning vehicle in this phase.

[0049] Total time for releasing vehicles shifting out of the ring left in phase 1 g o,1 See equations (8), (9), and (10):

[0050] t1=(X c,1 +L2+L y,1 ) / v1 (8)

[0051] t3=(X c,3 +L4+L y,3 ) / v1 (9)

[0052] g o,1 =l+max(t1,t3) (10)

[0053] Total time for releasing vehicles shifting out of the ring left in phase 2 g o,2 See formula (11), (12), (13):

[0054] t2=(X c,2 +L3+L y,2 ) / v1 (11)

[0055] t4=(Xc,4 +L1+L y,4 ) / v1 (12)

[0056] g o,2 =l+max(t2,t4) (13)

[0057] Further, in step 3-3, the release time of the straight-going vehicle is determined according to the release time of the left-turning vehicle entering the ring, the release time of the left-turning vehicle leaving the ring, the advance start time and the straight-going green light interval time, specifically:

[0058] The green light interval time for going straight indicates the time required to ensure that the last straight vehicle can pass the conflict point before the vehicle that shifts left into the ring in the next phase reaches the conflict point. The calculation method is:

[0059] The green light interval time I1 of a straight line in phase is as follows:

[0060] I s,1 =L s,1 / v2-(X r,2 +L y,2 ) / v1 (14)

[0061] I s,3 =L s,3 / v2-(X r,4 +L y,4 ) / v1 (15)

[0062] I1=max(I s,1 ,I s,3 ) (16)

[0063] The green light interval for going straight should be the larger value between the two directions to ensure that there will be no conflict in the other direction.

[0064] Phase 2 straight green light interval time I2, see equations (17), (18), (19):

[0065] I s,2 =L s,2 / v2-(X r,3 +L y,3 ) / v1 (17)

[0066] I s,4 =L s,4 / v2-(X r,1 +L y,1 ) / v1 (18)

[0067] I2=max(I s,2 ,I s,4 ) (19)

[0068] In formulas (14) to (19), I s,1 ,I s,2 ,I s,3 ,I s,4 Respectively represent the green light interval time for the south, east, north and west entrance lanes. s,1 , L s,2 , L s,3 , L s,4 Respectively represent the length of the tail clearance area for straight traffic on the south, east, north and west entrance roads, X r,1 , X r,2 , X r,3 , X r,4 They represent the length of the left-turn zone in the south, east, north and west directions respectively; v2 represents the average speed of the vehicle under continuous operation; and v1 represents the average speed of the vehicle under stationary start condition;

[0069] The straight green light time of the entire phase is equal to the sum of the green light time of the left-turning vehicle entering the ring and the green light time of the left-turning vehicle leaving the ring minus the advance start time of the phase, and then minus the straight green light interval time of the phase, see equations (20) and (21):

[0070] g s,1 =g a,1 +g o,1 -t o,1 -I1 (20)

[0071] g s,2 =g a,2 +g o,2 -t o,2 -I2 (21)

[0072] Among them, g a,1 , g a,2 , g o,1 , g o,2 ,t o,1 and t o,2 Determined based on the calculation results of steps 3-1 and 3-2.

[0073] Furthermore, in step 3-4, the pedestrian crossing timing determines the pedestrian crossing release method and release time, specifically: the pedestrian crossing signal is consistent with the vehicle flow release direction, and the time is the duration of a single phase.

[0074] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0075] According to the roundabout signal timing scheme based on shifted left turn and secondary parking, left-turning vehicles on the roundabout can directly turn left in a short distance without going around the central island for about 270 degrees. The method is suitable for large roundabouts, especially during peak hours, when the traffic capacity is high. The method is suitable for roundabouts with a large left-turn traffic volume, and the release of left-turning vehicles is optimized, the traffic capacity of left-turning vehicles is large, and the delay is reduced. The timing scheme of the method has a small number of phases, a short cycle time, and a short waiting time in queues in all directions. According to the method, right-turning vehicles can pass all the way without waiting in queues, and only need to abide by road traffic regulations and pay attention to giving way to pedestrians. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 A schematic diagram of the functional division of lanes in a roundabout according to the present invention;

[0077] Figure 2 is a channelization diagram of a roundabout according to the present invention;

[0078] Figure 3 It is a schematic diagram of geometric parameters of the roundabout of the present invention;

[0079] Figure 4 It is a timing schematic diagram of the present invention;

[0080] Figure 5 This is a current status diagram of the satellite square in the embodiment;

[0081] Figure 6 This is the satellite square timing diagram in the embodiment. DETAILED DESCRIPTION

[0082] For the convenience of description, the present invention names the intersections according to the four directions of east, south, west and north, but this does not limit the application of the present invention, and this statement applies to all descriptions of the present invention based on directions.

[0083] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings.

[0084] The present invention is applicable to the following traffic organization mode: the passing order of left-turning vehicles is to first shift and turn left, then directly turn left to the waiting area of ​​the left-turn roundabout to stop and wait, then drive out of the roundabout, and then shift to the normal lane through the shifted left-turn area.

[0085] The present invention provides a roundabout signal timing method based on shifted left turn and secondary parking, which is performed according to the following steps:

[0086] Step 1: Investigate the geometric conditions and traffic volume of the roundabout; determine the layout of the shifted left-turn lane at the roundabout; set up traffic lights at the roundabout, and set up corresponding traffic signs and markings.

[0087] Step 1-1: Investigate the geometric conditions of the roundabout:

[0088] Measure the road width of each entrance road of the roundabout, the width of the ring road, the width of the sidewalk, the length of the left-turn ring road waiting area, the length of the straight traffic clearing area, the length of the left-turn entry ring area and the length of the left-turn exit ring area, such as Figure 1 and Figure 3 As shown;

[0089] The length of the waiting area of ​​the left-turn roundabout is the length of the inner roundabout area where vehicles transferring left into the roundabout queue up; the length of the straight-moving traffic clearing area is the length of the straight-moving vehicles passing the left-turn conflict point in the next phase; the length of the left-turn entry area is the length from the entrance road displacement section to the inner section of the roundabout; the length of the left-turn exit area is the length from the inner section of the roundabout to the exit road displacement section.

[0090] Step 1-2: Survey traffic volume at the roundabout:

[0091] Investigate the flow rate and direction of entrances in all directions, the pedestrian, non-motor vehicle and motor vehicle traffic volume and their composition at each entrance, and the cross-sectional flow rate of the roundabout; investigate the average driving speed of vehicles under stationary starting conditions, investigate the average driving speed of vehicles when they are running continuously; investigate the average headway distance when vehicles are stopped; investigate the average time it takes for a single vehicle to pass the stop line.

[0092] Steps 1-3, such as Figure 1 and Figure 3 As shown in the figure, determine the number of shifted left-turn lanes at the roundabout, the number of lanes in the left-turn connection area of ​​the entrance road, the position of the shifted left-turn area and the length of the shifted section:

[0093] The left-turn connection area of ​​the entrance road refers to the connecting road section behind the left-turn stop line.

[0094] The number of shifted left-turn lanes at the roundabout and the number of left-turn lanes in the left-turn connection area of ​​the entrance road are determined according to the left-turn traffic volume at the roundabout. The position of the shifted left-turn area and the length of the shifted section are determined according to the actual situation of the intersection, where the length of the shifted section is the length of the lane in the shifted left-turn area.

[0095] Step 1-4, setting the number of lanes and the starting and ending positions and the position of the secondary stop line of the left-turn lane waiting area of ​​the roundabout according to the number and position of the shifted left-turn lanes;

[0096] The number of lanes in the waiting area of ​​the left-turn ring road of the roundabout should be consistent with the number of shifted left-turn lanes. The left-turn entry and exit positions of the roundabout area are determined according to the positions of the shifted left-turn lanes.

[0097] Secondary parking refers to the passage of left-turning vehicles. Not only do they need to stop and queue at the first left-turn parking line, but they also need to stop a second time at the second parking line in the waiting area of ​​the left-turn roundabout before leaving the roundabout. The second parking line is the position where the left-turning vehicles start queuing on the roundabout. Figure 1 shown.

[0098] Steps 1-5: Set up traffic lights at the roundabout, and set up corresponding traffic signs and markings;

[0099] like Figure 2 As shown, the traffic lights at the roundabout are set, specifically: Z1, Z2, Z3, and Z4 are set as the left-turning vehicle entering the roundabout in the four directions of south, east, north, and west; H1, H2, H3, and H4 are set as the secondary stop line lights in the four directions of south, east, north, and west, that is, the left-turning vehicle exiting the roundabout; S1, S2, S3, and S4 are set as the straight-ahead vehicle lights in the four directions of south, east, north, and west; R1, R2, R3, and R4 are set as the pedestrian crossing lights in the four directions of south, east, north, and west. At the same time, special traffic signs and markings are set for the shifted left-turning vehicles to ensure that the left-turning vehicle drivers can clearly understand the driving route.

[0100] Step 2: Design the phase of the traffic lights to ensure that the roundabout adopts a two-phase traffic rule.

[0101] Determine the two-phase traffic rules for roundabouts, specifically:

[0102] In the first phase, the north-south entrance lane phase is the key phase, and the north-south left turn secondary stop phase is divided into the first half of the shifted left turn lane phase and the second half of the left turn ring road waiting phase. The two phases share the north-south key phase duration;

[0103] In the second phase, the east-west entrance lane phase is the key phase, and the east-west left turn is a second stop. The phase is divided into the first half of the shifted left turn lane phase and the second half of the left turn ring road waiting zone phase. The two phases share the length of the east-west key phase.

[0104] Step 3: With no traffic conflicts as the condition and the maximum capacity of the roundabout as the goal, determine the travel time of straight and right-turning vehicles based on the travel time of the second left-turning vehicles, and determine the roundabout signal timing method, which specifically includes the timing of left-turning vehicles entering the roundabout, the timing of left-turning vehicles leaving the roundabout, the timing of straight-moving vehicles, and the timing of pedestrians crossing the street.

[0105] To set the timing scheme for the shifted left turn and secondary parking roundabout, first define the variables used in the timing, see Table 1.

[0106] Table 1 Timing related parameter definition table

[0107]

[0108] like Figure 3 and Figure 4As shown, the roundabout signal timing method specifically includes the following steps:

[0109] Step 3-1: Timing of vehicles entering the ring for left shifting, determine the release method and release time of vehicles entering the ring for left shifting:

[0110] Vehicles that shift left into the roundabout are defined as left-turning vehicles that first shift left in the four directions of east, west, south, and north, and then enter the waiting area of ​​the left-turn roundabout to queue up.

[0111] The release method for vehicles shifting to the left in phase 1 is to set green lights on the left-turn entrance lanes Z1 and Z3, and the green light time is the first part of phase 1. The left-turn vehicles are released to queue in the waiting area of ​​the left-turn roundabout. When the maximum release time is reached or the waiting area of ​​the left-turn roundabout is full, the light turns red; that is, the left-turn vehicles at the north-south entrance shift into the waiting area of ​​the left-turn roundabout at the roundabout, and queue at the secondary stop line of the H2 and H4 signal lights to wait for release;

[0112] The method for releasing vehicles that shift left into the roundabout during Phase 2 is to set green lights at the left-turn entrance lanes Z2 and Z4. The green light time is the first part of Phase 2. Left-turn vehicles are released to queue in the waiting area of ​​the left-turn roundabout. When the maximum release time is reached or the waiting area of ​​the left-turn roundabout is full, the light turns red. That is, left-turn vehicles at the east-west entrances shift into the waiting area of ​​the left-turn roundabout at the roundabout and queue at the secondary stop line of the H1 and H3 traffic lights to wait for release.

[0113] The release time for vehicles entering the left-turn roundabout is determined by the maximum number of parked vehicles in the waiting area of ​​the left-turn roundabout, the length of the waiting area of ​​the left-turn roundabout, the average headway distance between vehicles when they stop, the average time for a single vehicle to pass the stop line and the starting loss time.

[0114] Among them, the maximum number of parked vehicles in the waiting area of ​​the left-turn roundabout indicates the maximum number of left-turn vehicles that can be parked in this area; the length of the waiting area of ​​the left-turn roundabout indicates the actual length of the waiting area of ​​the left-turn roundabout; the average headway distance when vehicles stop indicates the average headway distance when vehicles are parked in a queue in this area; the average time for a single vehicle to pass the stop line refers to the average time for queued vehicles to pass the stop line from stationary to stationary.

[0115] The calculation method for the release time of vehicles entering the ring with a left shift is as follows:

[0116] The maximum number of parked vehicles N in the waiting area of ​​the left-turn roundabout in the i-th direction i Equal to the length of the waiting area for the left turn in this direction, L i Divide by the average headway S when the vehicles are stopped, see formula (1):

[0117] N i =L i / S (1)

[0118] The green light time g of the vehicle entering the ring at the left transfer position in the i-th direction LiEqual to the maximum number of parked vehicles N in the waiting area of ​​the left-turn roundabout in this direction i Multiply it by the average time t for a single vehicle to pass the stop line, see formula (2):

[0119]

[0120] Due to the adoption of opposite release, in order to ensure that the left-turning vehicles entering the ring from the other direction will not overflow the left-turn ring waiting area, the green light time of the left-turning vehicles entering the ring in the phase is equal to the smaller value of the green light time of the left-turning vehicles entering the ring in the two opposite directions. Add the startup loss time l, which is determined by investigation, as shown in formulas (3) and (4):

[0121]

[0122]

[0123] Step 3-2: Timing of vehicles shifting out of the left turn ring, determine the release method and release time of vehicles shifting out of the left turn ring:

[0124] A left-turning out-of-loop displaced vehicle is defined as a left-turning vehicle that first exits the left-turn loop waiting area and then enters the normal lane after a displaced operation.

[0125] The left-turn exit shift timing plan refers to the green light time of the signal lights H1, H2, H3, and H4 in the waiting area of ​​the left-turn roundabout. In this case, it is necessary to ensure that all left-turning vehicles in the waiting area of ​​the left-turn roundabout completely drive out of the shift point and reach the basic road section.

[0126] The method for releasing vehicles that turn left out of the loop in Phase 1 is that the H1 and H3 loop lights are green, and the green light time is the last part of Phase 1. After the Z1 and Z3 lights are red, the H1 and H3 left-turning vehicles exit the loop and enter the shifted lane; that is, vehicles turning left from the east-west direction exit the loop through the H1 and H3 signal lights and shift into the north-south direction.

[0127] The method for releasing vehicles that turn left out of the loop in phase two is that the H2 and H4 loop lights are green, and the green light time is the last part of phase one. After the Z2 and Z4 lights are red, the H2 and H4 left-turning vehicles exit the loop and enter the shifted lane; that is, vehicles turning left from the north-south direction exit the loop through the H2 and H4 lights and shift into the east-west direction.

[0128] The method for calculating the release time of vehicles turning left out of the ring is as follows:

[0129] The release time for vehicles displaced when turning left out of the roundabout is determined by the length of the left-turn exit area, the length of the waiting area for the left-turn roundabout, the length of the displaced left-turn area, the average driving speed of the vehicle under stationary starting conditions and the starting loss time; among which the average driving speed of the vehicle under stationary starting conditions refers to the average speed of the vehicle from starting from rest to exiting the roundabout.

[0130] Constraints: In the same phase, there is a release order for left-shifted vehicles entering the ring and left-turning vehicles leaving the ring. The left-shifted vehicles entering the ring are released first through signal control, and then the left-turning vehicles leaving the ring are released. Due to the existence of the left-turning exit area, there is a time difference between the two. The signal can be used to release the left-turning vehicles leaving the ring before the left-shifted vehicles entering the ring are released. This is defined as the advance start time t f,i , calculated as the length of the left turn loop area of ​​the i entrance road X c,i The ratio of the average speed v1 of the vehicle under static starting conditions is shown in formula (5):

[0131] t f,i =X c,i / v1 (5)

[0132] The same opposite direction release is adopted. The green light of the vehicle shifting out of the left turn ring is started in advance by time t o,1 ,t o,2 Choose two relative directions t f,i The smaller value of t is used to ensure that when the left-turning out-of-loop displaced vehicle reaches the displaced left-turn area, the left-turning in-loop vehicles have been released. The green light advance start time for the left-turning out-of-loop displaced vehicle in a single phase is equal to the smaller advance start time min (t f,i ) plus the start-up loss time l, the green light advance start time of the left-turn out-of-ring shift vehicle in the two phases is shown in equations (6) and (7):

[0133] t o,1 = l + min (t f,i ) (i is the first phase release direction) (6)

[0134] t o,2 = l + min (t f,i ) (i is the second phase release direction) (7)

[0135] The total release time of a phase must ensure that the last left-turning vehicle in both directions passes through the displaced left-turn area. The calculation method is: calculate the ratio of the sum of the lengths of the left-turning exit area, the waiting area of ​​the left-turning ring, and the displaced left-turn area in the two relative directions to the average driving speed v1 of the vehicle under stationary starting conditions. The larger value between the two relative directions is selected as the ratio, and then the starting loss time is added as the total release time of the left-turning vehicles in this phase.

[0136] Total time for releasing vehicles shifting out of the ring left in phase 1 g o,1 See equations (8), (9), and (10):

[0137] t1=(X c,1 +L2+L y,1 ) / v1 (8)

[0138] t3=(X c,3 +L4+L y,3 ) / v1 (9)

[0139] g o,1 =l+max(t1,t3) (10)

[0140] Total time for releasing vehicles shifting out of the ring left in phase 2 g o,2 See formula (11), (12), (13):

[0141] t2=(X c,2 +L3+L y,2 ) / v1 (11)

[0142] t4=(X c,4 +L1+L y,4 ) / v1 (12)

[0143] g o,2 =l+max(t2,t4) (13)

[0144] Step 3-3: Timing of through vehicles: Determine the release method and time of through vehicles:

[0145] The through-the-way phase timing plan includes the green light time of the through-the-way signal lights S1, S2, S3, and S4, i.e., the release time for through-the-way vehicles in the four directions of south, east, north, and west.

[0146] The method for releasing vehicles going straight in phase is that the S1 and S3 straight lights are green, that is, the straight vehicles in the north-south direction pass the S1 and S3 lights and go straight through the roundabout;

[0147] The method for releasing through vehicles in phase 2 is that the S2 and S4 through lights are green, that is, through vehicles in the east-west direction pass the S2 and S4 lights and go straight through the roundabout;

[0148] The green light time for vehicles going straight is calculated as follows:

[0149] The timing plan for through vehicles mainly considers ensuring that the last through vehicle can pass the conflict point before the end of the phase, ensuring the normal release of the next phase. The release time of through vehicles is determined based on the release time of left-shifting vehicles entering the ring, the release time of left-turning vehicles leaving the ring, the advance start time and the straight green light interval time.

[0150] The straight green light interval time indicates the time required to ensure that the last straight vehicle can pass the conflict point before the vehicle that shifts left into the ring in the next phase reaches the conflict point. The calculation method is:

[0151] The green light interval time I1 of a straight line in phase is as follows:

[0152] I s,1 =L s,1 / v2-(X r,2 +L y,2 ) / v1 (14)

[0153] I s,3 =L s,3 / v2-(X r,4 +L y,4 ) / v1 (15)

[0154] I1=max(I s,1 ,I s,3 ) (16)

[0155] The green light interval for going straight should be a larger value between the two directions to ensure that there will be no conflict in the other direction.

[0156] Phase 2 straight green light interval time I2, see equations (17), (18), (19):

[0157] I s,2 =L s,2 / v2-(X r,3 +L y,3 ) / v1 (17)

[0158] I s,4 =L s,4 / v2-(X r,1 +L y,1 ) / v1 (18)

[0159] I2=max(I s,2 ,I s,4 ) (19)

[0160] In formulas (14) to (19), I s,1 ,I s,2 ,I s,3 ,I s,4 Respectively represent the green light interval time for the south, east, north and west entrance lanes. s,1 , L s,2 , L s,3 , L s,4 Respectively represent the length of the tail clearance area for straight traffic on the south, east, north and west entrance roads, X r,1 , X r,2 , X r,3 , X r,4They represent the length of the left-turn zone in the south, east, north and west directions respectively; v2 represents the average speed of the vehicle under continuous operation; and v1 represents the average speed of the vehicle under stationary start condition;

[0161] The straight green light time of the entire phase is equal to the sum of the green light time for the vehicle entering the ring to the left and the green light time for the vehicle leaving the ring to the left, minus the advance start time of the phase, and then minus the straight green light interval time of the phase, see formula (20)(21).

[0162] g s,1 =g a,1 +g o,1 -t o,1 -I1 (20)

[0163] g s,2 =g a,2 +g o,2 -t o,2 -I2 (21)

[0164] Among them, g a,1 , g a,2 , g o,1 , g o,2 ,t o,1 and t o,2 Determined based on the calculation results of steps 3-1 and 3-2.

[0165] Cycle duration:

[0166] c=g s,1 +I1+g s,2 +I2 (22)

[0167] Step 3-4: Timing of pedestrian crossings: determine the method and time of releasing pedestrians:

[0168] The time to release pedestrians crossing the street is determined by the duration of a single phase;

[0169] The pedestrian crossing signal of this scheme is consistent with the direction of vehicle release. Phase 1 releases pedestrians crossing the street in the north-south direction, and phase 2 releases pedestrians crossing the street in the east-west direction. The time is the entire phase duration.

[0170] The final timing calculation result is as follows: Figure 4 shown.

[0171] Step 3-5: The phase in the other direction is determined in the same manner as in steps 3-1 to 3-4.

[0172] Example

[0173] The present invention will be described in more detail below with reference to the accompanying drawings.

[0174] Satellite Plaza is located in the southern part of Changchun City, at the intersection of Renmin Street, the central axis of Changchun City, and Satellite Road in the middle section of the Southern Expressway. The diameter of the central island of Satellite Plaza is 140m, the diameter of the roundabout is 200m, and the total area of ​​the roundabout is 31,416m 2 The square is planted with multiple layers of plants, reflecting the natural ecology of Changchun and the green welcoming forest city style. The square is mainly surrounded by colleges and universities, commercial centers and residential areas, with convenient public transportation, multiple ground regular bus stops in all directions, and is within the 600m radius coverage of the transfer station of Changchun Metro Line 1 and Line 3.

[0175] Step 1: Investigate the geometric conditions and traffic volume of the roundabout; determine the layout of the shifted left-turn lane of the roundabout; set up the roundabout entrance road, shifted left-turn lane, and traffic lights in the left-turn waiting area, and set up corresponding traffic signs and markings;

[0176] Step 1-1: Investigate the geometric conditions of the roundabout:

[0177] The south entrance and exit of Renmin Street is a two-way 10-lane road with a 4-lane section, and the north entrance and exit is a 9-lane road with a 3-lane section; the east entrance and exit of Satellite Plaza is a 7-lane road, and the west entrance and exit is an 8-lane road with a 2-lane section. There is also a 4-lane south expressway tunnel in the east-west direction. The square has been designed with traffic channelization for entrances and exits, weaving areas, circulation areas, pedestrians and non-motor vehicles, and adopts a two-phase signal control form for opposite release. There is no functional division of the entrance turn lane. The specific details are as follows Figure 5 shown.

[0178] At present, there are 4 single-point control signal lights in Satellite Square, which are located at the 4 entrances of Renmin Avenue and Satellite Road. The release mode is north-south and east-west opposite release. The green light duration is 84s, the red light duration is 87s, and the yellow light duration is 3s. This kind of traffic organization and timing is prone to merging due to traffic conflicts during peak hours. The traffic conflicts are serious, and the phase difference setting is unreasonable. The intersection is prone to lock, causing the queued traffic to overflow the roundabout and affect the traffic of the road section. At the same time, there is no crossing signal for pedestrians. Pedestrians crossing the street rely entirely on motor vehicles to stop and give way, which aggravates the congestion at the intersection during peak hours.

[0179] Step 1-2: Survey traffic volume at the roundabout:

[0180] According to the traffic volume survey, the proportion of left-turn traffic in each direction of Satellite Plaza is shown in Table 2 and Table 3.

[0181] Table 2 Satellite Plaza Peak Traffic Volume Proportion

[0182]

[0183] Table 3 Satellite Plaza Peak Traffic Volume Proportion

[0184]

[0185] According to the current survey results, the proportion of left-turning vehicles at each entrance direction of the Satellite Plaza is relatively high. Combined with existing research, under the conditions of high left-turn traffic volume and large proportion of left straight traffic volume, setting it as a shifted left-turn roundabout can achieve ideal results. In the above case, the number of shifted left-turn lanes is reasonably set to reduce the average delay of vehicles, and at the same time, the left-turning vehicles do not need to drive around the circle 270°, which can reduce intersection conflicts, improve the traffic capacity of the roundabout, and reduce the traffic pressure in the roundabout. The cross-sectional flow of the roundabout before and after the direct left turn is set is shown in Table 4.

[0186] Table 4 Set the flow rate of the loop section before and after the direct left turn pcu / h

[0187]

[0188]

[0189] As a new type of intersection different from traditional intersections, the shifted left-turn intersection can effectively realize the simultaneous release and conflict-free driving of left-turning vehicles and oncoming straight vehicles, thereby reducing the number of signal phases and vehicle conflicts. According to the current situation, the satellite square is considered to adopt a shifted left-turn channelization transformation method.

[0190] According to Tables 2 and 3, the Satellite Plaza should have two left-turn lanes to meet the traffic needs of left-turning vehicles.

[0191] Step 1-3, determine the number of shifted left-turn lanes at the roundabout, the number of left-turn lanes at the entrance road connection section, the position of the shifted left-turn area and the length of the shifted section;

[0192] According to Table 2 and Table 3, the left-turn traffic volume in the satellite square accounts for a high proportion, both around 30%. This plan sets up two dedicated shifted left-turn lanes for left-turn vehicles. The shifted left-turn areas in the south, north, east and west directions are located 10 meters away from the current parking line. Considering the large left-turn traffic volume, the shifted left-turn area is set to be 15 meters long along the road direction.

[0193] Step 1-4, setting the number of lanes and the starting and ending positions and the position of the secondary stop line of the left-turn lane waiting area of ​​the roundabout according to the number and position of the shifted left-turn lanes;

[0194] This plan sets up two shifted left-turn lanes, two left-turn roundabout waiting area lanes, and a secondary parking line.

[0195] Steps 1-5: Set up traffic lights at the roundabout, and set up corresponding traffic signs and markings;

[0196] like Figure 2 As shown, the traffic lights at the roundabout are set, specifically: Z1, Z2, Z3, and Z4 are set as the signal lights for vehicles entering the roundabout on the left side in the south, east, north, and west directions; H1, H2, H3, and H4 are set as the secondary stop line signal lights in the south, east, north, and west directions, that is, the signal lights for vehicles turning left out of the roundabout; S1, S2, S3, and S4 are set as the signal lights for vehicles going straight in the south, east, north, and west directions; R1, R2, R3, and R4 are set as the signal lights for pedestrians crossing the street in the south, east, north, and west directions. At the same time, special traffic signs and markings are set for vehicles turning left to ensure that drivers of left-turning vehicles can clearly understand the driving route.

[0197] Step 3: Determine the travel time of the straight and right-turn vehicles according to the travel time of the second left-turn vehicle, and determine the roundabout signal timing method, which specifically includes:

[0198] Step 3-1: Timing of vehicles entering the ring for left shifting, determine the release method and release time of vehicles entering the ring for left shifting:

[0199] The release method for vehicles shifting to the left in phase 1 is to set green lights on the left-turn entrance lanes Z1 and Z3, and the green light time is the first part of phase 1. The left-turn vehicles are released to queue in the waiting area of ​​the left-turn roundabout. When the maximum release time is reached or the waiting area of ​​the left-turn roundabout is full, the light turns red; that is, the left-turn vehicles at the north-south entrance shift into the waiting area of ​​the left-turn roundabout at the roundabout, and queue at the secondary stop line of the H2 and H4 signal lights to wait for release;

[0200] The release method for vehicles shifting to the left in phase 2 is to set green lights on the left-turn entrance lanes Z2 and Z4, and the green light time is the first part of phase 2. The left-turn vehicles are released to queue in the waiting area of ​​the left-turn roundabout. When the maximum release time is reached or the waiting area of ​​the left-turn roundabout is full, the light turns red; that is, the left-turn vehicles at the east-west entrances are shifted to the waiting area of ​​the left-turn roundabout at the roundabout, and queue at the secondary stop line of the H1 and H3 signal lights to wait for release;

[0201] According to the survey results of the satellite square, the average headway s of the vehicles when they are stopped is 7m, and the roundabout radius is 70m. Figure 4 Parameter description: the length of the waiting area for left-turn loop in each direction L i The length of the left turn lane is 110 m. According to formula (1), the maximum number of parked vehicles in the waiting area of ​​the left turn lane is 16. According to the survey, the average time T for a single vehicle to pass the stop line is 1.8 s, and the starting loss time l is 2 s. According to formulas (2), (3), and (4), the green light time g of the left turn lane vehicle entering the lane in the two phases is a,1 and g a,2 Both are 31s.

[0202] Step 3-2: Timing of vehicles shifting out of the left turn ring, determine the release method and release time of vehicles shifting out of the left turn ring:

[0203] The release method for displaced vehicles turning left out of the loop in Phase 1 is as follows: when the H1 and H3 loop lights turn green, the green light time is the last part of Phase 1, and after the Z1 and Z3 lights turn red, the H1 and H3 left-turning vehicles exit the loop and enter the displaced lane; that is, the east-west left-turning vehicles exit the loop through the H1 and H3 lights and displace into the north-south direction;

[0204] The method for releasing vehicles that turn left out of the ring in phase two is: the H2 and H4 ring road traffic lights are green, and the green light time is the last part of phase one. After the Z2 and Z4 lights are red, the H2 and H4 left-turning vehicles exit the ring and enter the shifted lane; that is, vehicles turning left from the north-south direction exit the ring through the H2 and H4 traffic lights and shift into the east-west direction; when in the same phase, there is a release order for vehicles that shift left into the ring and vehicles that shift left out of the ring. Through signal control, left-turning vehicles are released into the ring first, and then left-turning vehicles are released.

[0205] According to the survey, the average speed v1 of the vehicle under static starting conditions is 23km / h, which is converted to 6.4m / s. The length of the left turn loop in each direction is X c,i They are 42.5m in the south, 52m in the east, 58m in the north, and 58m in the west. According to formula (5), the early start loss time in each direction is t f,1 is 7s, east direction t f,2 is 8s, north direction t f,3 is 9s, west direction t f,4 is 9s. The starting loss time l is 2s. From (6) and (7), we can get that the phase 1 advance starting time t o,1 9s, phase 2 advance start time t o,2 is 10s.

[0206] According to the plan, the length of the displacement section of the entrance channel in each direction is L y,i They are 17m for the south, 32m for the east, 16m for the north, and 16m for the west. According to (8)(9)(11)(12), the total green light time for vehicles turning left out of the ring in the four directions is 27s for the south, 30s for the east, 29s for the north, and 29s for the west. The starting loss time l is 2s. According to (10)(13), the green light time g for vehicles turning left out of the ring in phase 1 is o,1 31s, green light time g for vehicles turning left out of the ring in phase 2 o,1 It is 32s.

[0207] Step 3-3: Timing of through vehicles: Determine the release method and time of through vehicles:

[0208] The method for releasing vehicles going straight in phase is that the S1 and S3 straight lights are green, that is, the straight vehicles in the north-south direction pass the S1 and S3 lights and go straight through the roundabout;

[0209] The method for releasing through vehicles in phase 2 is that the S2 and S4 through lights are green, that is, through vehicles in the east-west direction pass the S2 and S4 lights and go straight through the roundabout;

[0210] According to the survey, the average speed v2 of vehicles under continuous operation is 33km / h, which is converted to 9.2m / s. The length of the tail clearance area for straight traffic in each direction is L. s,i They are 133m in the south, 142m in the east, 146m in the north, and 148m in the west. Turn left in each direction and enter the loop area for a length of X r,i They are 42.5m in the south, 52m in the east, 58m in the north, and 58m in the west. The calculation shows that the time for straight traffic in each direction to pass the conflict point is 15s in the south, 16s in the east, 16s in the north, and 16s in the west. The time for the next phase to turn left and enter the roundabout is 9s in the south, 13s in the east, 11s in the north, and 11s in the west. From (14)(15)(17)(18), the green light interval time I for straight traffic on the entrance road in each direction is obtained: s,i They are 2s for the south, 5s for the east, 5s for the north, and 7s for the west. According to (16) and (19), the green light interval time I1 for the straight-going traffic in phase 1 is 5s, and the green light interval time I2 for the straight-going traffic in phase 2 is 7s.

[0211] Finally, according to (20)(21), the green light time g for phase 1 is s,1 48s, phase 2 straight green light time g s,2 It is 46s.

[0212] Step 3-4: Timing of pedestrian crossings: determine the method and time of releasing pedestrians:

[0213] According to the pedestrian green light time as the green light time of this phase, the pedestrian green light time for phase one is 53s, and the pedestrian green light time for phase two is 53s.

[0214] According to (22), the cycle length is 106s. The calculation results are shown in Table 5.

[0215] Table 5 Timing calculation results

[0216]

[0217]

[0218] The final timing results are shown in Figure 6 ,The results show that the effective green light time of the two phases is longer, which can effectively improve the ,capacity of the intersection and reduce conflicts; and the phase cycle duration is shorter, ,and the delays in all directions of the intersection are lower, which ,proves that the timing method is effective.

[0219] The above description is only a preferred specific implementation manner of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A roundabout signal timing method based on shifted left turn and secondary parking, characterized in that Follow these steps: Step 1: Investigate the geometric conditions and traffic volume of the roundabout; determine the layout of the shifted left-turn lane of the roundabout; set up traffic lights at the roundabout, and set up corresponding traffic signs and markings; Step 2: Design the phase of the signal lights to determine whether the roundabout adopts a two-phase traffic rule; Step 3: Under the condition of no traffic conflict and with the goal of maximizing the roundabout capacity, the traffic time of straight and right-turning vehicles is determined according to the traffic time of the second left-turning vehicle, and the roundabout signal timing method is determined, which specifically includes: Step 3-1: Timing of vehicles entering the ring for left shifting, determine the release method and release time of vehicles entering the ring for left shifting: The release time of vehicles entering the left-turn roundabout is determined by the maximum number of parked vehicles in the waiting area of ​​the left-turn roundabout, the length of the waiting area of ​​the left-turn roundabout, the average headway distance when the vehicles stop, the average time for a single vehicle to pass the stop line, and the start-up loss time. Specifically: The maximum number of parked vehicles N in the waiting area of ​​the left-turn roundabout in the i-th direction i Equal to the length of the waiting area for the left turn in this direction, L i Divide by the average headway S when the vehicles are stopped, see formula (1): N i =L i / S (1) Where N i is the maximum number of parked vehicles in the waiting area of ​​the left-turn roundabout on the i-entrance, L i is the length of the waiting area for the left-turn roundabout at the i-th entrance, where i is 1, 2, 3, and 4, representing the four entrance directions of south, east, north, and west respectively; The green light time g of the vehicle entering the ring at the left transfer position in the i-th direction Li Equal to the maximum number of parked vehicles N in the waiting area of ​​the left-turn roundabout in this direction i Multiply it by the average time t for a single vehicle to pass the stop line, see formula (2): The green light time for vehicles entering the ring in the left shift phase is equal to the smaller value of the green light time for vehicles entering the ring in the left shift phase in the two opposite directions. Add the startup loss time l, which is determined by investigation, as shown in formula (3) (4): In formula (3) and formula (4), g a,1 is the green light time for vehicles entering the ring when the phase shifts left, g a,2 The green light time for vehicles entering the ring at the left shift in phase 2; Step 3-2: Timing of vehicles shifting out of the left turn ring, determine the release method and release time of vehicles shifting out of the left turn ring: The release time of the displaced vehicle turning out of the left turn ring is determined by the length of the left turn ring area, the length of the waiting area of ​​the left turn ring, the length of the displaced left turn area, the average speed of the vehicle under the condition of stationary starting, and the starting loss time, specifically: Turn left out of the ring and enter the i direction green light early start time t f,i , calculated as the length of the left turn loop area of ​​the i entrance road X c,i The ratio of the average speed v1 of the vehicle under static starting conditions is shown in formula (5): t f,i =X c,i / v1 (5) In the formula, t f,i The green light for turning left out of the ring and entering the i direction starts in advance, X c,i is the length of the left-turn loop in direction i, v1 is the average speed of the vehicle under static starting conditions; Take the opposite direction release, the phase left turn ring shift vehicle green light early start time t o,1 ,t o,2 Choose two relative directions t f,i The smaller value ensures that when the left-turning out-of-ring shifting vehicle arrives at the shifted left-turn area, the left-turning in-ring shifting vehicle has been released; the green light advance start time of the left-turning out-of-ring shifting vehicle in a single phase is equal to the smaller advance start time min (t f,i ) plus the start-up loss time l, the green light advance start time of the left-turn out-of-ring shift vehicle in the two phases is shown in equations (6) and (7): t o,1 = l + min (t f,i ) (i is the first phase release direction) (6) t o,2 = l + min (t f,i ) (i is the second phase release direction) (7) In formula (6) and formula (7), t o,1 and t o,2 They are the green light advance start time for vehicles turning left out of the ring in phase 1 and phase 2 respectively; The total release time of a phase must ensure that the last left-turning vehicle in both directions passes through the shifted left-turn area. The calculation method is: calculate the ratio of the sum of the length of the left-turning loop area, the length of the waiting area of ​​the left-turning loop, and the length of the shifted left-turn area in the two relative directions to the average driving speed v1 of the vehicle under static starting conditions. The larger value between the two relative directions is selected as the ratio, and then the start loss time is added to it, which is taken as the total release time of the left-turning vehicle in this phase. Total time for releasing vehicles shifting out of the ring left in phase 1 g o,1 See equations (8), (9), and (10): t1=(X c,1 +L2+L y,1 ) / v1 (8) t3=(X c,3 +L4+L y,3 ) / v1 (9) g o,1 =l+max(t1,t3) (10) Total time for releasing vehicles shifting out of the ring left in phase 2 g o,2 See formula (11), (12), (13): t2=(X c,2 +L3+L y,2 ) / v1 (11) t4=(X c,4 +L1+L y,4 ) / v1 (12) g o,2 =l+max(t2,t4) (13) In equations (8) to (13), t1, t2, t3, and t4 are the green light times for vehicles turning left from the south, east, north, and west directions, respectively. c,1 , X c,2 , X c,3 , X c,4 L1, L2, L3, L4 are the lengths of the left-turn exit areas in the south, east, north, and west directions respectively. L y,1 , L y,2 , L y,3 , L y,4 are the lengths of the displacement sections of the south, east, north and west entrances, g o,1 and g o,2 are the green light time of the vehicle turning left out of the ring in phase 1 and phase 2 respectively, and l is the starting loss time; Step 3-3: Timing of through vehicles: Determine the release method and time of through vehicles: The release time of straight-going vehicles is determined according to the release time of left-turning vehicles entering the ring, the release time of left-turning vehicles leaving the ring, the advance start time and the straight-going green light interval time, specifically: The green light interval time for going straight indicates the time required to ensure that the last straight vehicle can pass the conflict point before the vehicle that shifts left into the ring in the next phase reaches the conflict point. The calculation method is: The green light interval time I1 of a straight line in phase is as follows: I s,1 =L s,1 / v2-(X r,2 +L y,2 ) / v1 (14) I s,3 =L s,3 / v2-(X r,4 +L y,4 ) / v1 (15) I1=max(I s,1 ,I s,3 ) (16) The green light interval for going straight should be the larger value between the two directions to ensure that there will be no conflict in the other direction. Phase 2 straight green light interval time I2, see equations (17), (18), (19): I s,2 =L s,2 / v2-(X r,3 +L y,3 ) / v1 (17) I s,4 =L s,4 / v2-(X r,1 +L y,1 ) / v1 (18) I2=max(I s,2 ,I s,4 ) (19) In formulas (14) to (19), I s,1 ,I s,2 ,I s,3 ,I s,4 Respectively represent the green light interval time for the south, east, north and west entrance lanes. s,1 , L s,2 , L s,3 , L s,4 Respectively represent the length of the tail clearance area for straight traffic on the south, east, north and west entrance roads, X r,1 , X r,2 , X r,3 , X r,4 They represent the length of the left-turn zone in the south, east, north and west directions respectively; v2 represents the average speed of the vehicle under continuous operation; and v1 represents the average speed of the vehicle under stationary start condition; The straight green light time of the entire phase is equal to the sum of the green light time of the left-turning vehicle entering the ring and the green light time of the left-turning vehicle leaving the ring minus the advance start time of the phase, and then minus the straight green light interval time of the phase, see equations (20) and (21): g s,1 =g a,1 +g o,1 -t o,1 -I1 (20) g s,2 =g a,2 +g o,2 -t o,2 -I2 (21) In formulas (20) and (21), g s,1 and g s,2 They are the straight green light time for phase 1 and phase 2 respectively. Among them, g a,1 , g a,2 , g o,1 , g o,2 ,t o,1 and t o,2 Determined based on the calculation results of step 3-1 and step 3-2; Step 3-4: Timing of pedestrian crossings: determine the method and time of releasing pedestrians: The time to release pedestrians crossing the street is determined by the duration of a single phase; Step 3-5: The phase in the other direction is determined in the same manner as in steps 3-1 to 3-4.

2. The roundabout signal timing method based on shifted left turn and secondary parking according to claim 1 is characterized in that: The timing method is applicable to the following traffic organization mode: the passage order of left-turning vehicles is to first shift left, then directly turn left to the waiting area of ​​the left-turn roundabout to stop and wait, then drive out of the roundabout, and then shift to the normal lane through the shift left-turn area.

3. The roundabout signal timing method based on shifted left turn and secondary parking according to claim 1, characterized in that: In step 1, the investigation of the geometric conditions and traffic volume of the roundabout specifically includes the following steps: Step 1-1: Investigate the geometric conditions of the roundabout: Measure the road width of each entrance road of the roundabout, the width of the ring road, the width of the sidewalk, the length of the waiting area of ​​the left-turn ring road, the length of the tail-clearing area of ​​the straight traffic flow, the length of the shift section, the length of the left-turn entry ring area and the length of the left-turn exit ring area; Step 1-2: Survey traffic volume at the roundabout: Investigate the flow rate and direction of entrances in all directions, the pedestrian, non-motor vehicle and motor vehicle traffic volume and their composition at each entrance, and the cross-sectional flow rate of the roundabout; investigate the average driving speed of vehicles under stationary starting conditions, investigate the average driving speed of vehicles when they are running continuously; investigate the average headway distance when vehicles are stopped; investigate the average time it takes for a single vehicle to pass the stop line.

4. The roundabout signal timing method based on shifted left turn and secondary parking according to claim 1, characterized in that: In step 1, determining the layout of the shifted left-turn lane at the roundabout specifically includes the following steps: Step 1-3, determine the number of shifted left-turn lanes at the roundabout, the number of lanes in the left-turn connection area of ​​the entrance road, the position of the shifted left-turn area and the length of the shifted section; Steps 1-4: Set the number of lanes, start and end positions, and secondary stop line position of the left-turn lane waiting area of ​​the roundabout according to the number and position of the shifted left-turn lanes.

5. The roundabout signal timing method based on shifted left turn and secondary parking according to claim 1, characterized in that: The setting of the traffic lights at the roundabout is specifically as follows: setting Z1, Z2, Z3, and Z4 as left-turning vehicle-entering-the-roundabout signal lights in the four directions of south, east, north, and west; setting H1, H2, H3, and H4 as secondary stop line signal lights in the four directions of south, east, north, and west, that is, left-turning vehicle-exiting-the-roundabout signal lights; setting S1, S2, S3, and S4 as straight-ahead vehicle signal lights in the four directions of south, east, north, and west; and setting R1, R2, R3, and R4 as pedestrian crossing signal lights in the four directions of south, east, north, and west.

6. The roundabout signal timing method based on shifted left turn and secondary parking according to claim 1, characterized in that: In step 2, the two-phase traffic rule is determined to be adopted at the roundabout, specifically: In the first phase, the north-south entrance lane phase is the key phase, and the north-south left turn secondary stop phase is divided into the first half of the shifted left turn lane phase and the second half of the left turn ring road waiting phase. The two phases share the north-south key phase duration; In the second phase, the east-west entrance lane phase is the key phase, and the east-west left turn is a second stop. The phase is divided into the first half of the shifted left turn lane phase and the second half of the left turn ring road waiting zone phase. The two phases share the length of the east-west key phase.

7. The roundabout signal timing method based on shifted left turn and secondary parking according to claim 1, characterized in that: In step 3-4, the pedestrian crossing timing determines the pedestrian crossing release method and release time, specifically: the pedestrian crossing signal is consistent with the vehicle flow release direction, and the time is the duration of a single phase.

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