Exercise 5 - Traffic Signal Design Aditya Nugroho e

EXERCISE 5

TRAFFIC SIGNAL DESIGN

CE 5203 TRAFFIC FLOW AND CONTROL

ADITYA NUGROHO

HT083276E

DEPARTMENT OF CIVIL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE

2010

2

Department of Civil Engineering

CE 5203 Traffic Flow and Control

1.0 INTRODUCTION

Traffic signal design aim to allocate and synchronize the timing of traffic signals in an area, to reduce stops, vehicle delay or maximizing throughput. Two concepts are of important in understanding signalized intersection design and operation: 1) The time allocation of the 3600 seconds in an hour to conflicting movements and to "lost times" in the cycle. 2) The effect of right-turning vehicles on the operation of the intersection. In this Exercise 5 the objectives are: • To understand how to design signal settings • To obtain parameters for signal design • To design optimal signal settings

2.0 TRAFFIC SIGNAL DESIGN METHOD

2.1 Data collection

Data from study area were collected during the peak hour morning at Commonwealth Ave intersection. This is four-legged intersection on arterial road. Digital video camera was used to collect data on the field where record towards AYE exit. However, at some lane approaches it was not possible to cover the full queue because the issues of video visibility. The recording was done for 30 minutes. Simultaneously data on signal timing such cycle length, number of phases, phase length was collected by using lap timer. It should be note that in this exercise the number of vehicle flow only measured in 3 cycles thus converted to hourly volume.

2.2 Signalised intersection flow characteristic

2.2.1 Saturation flow, discharge headway, and lost time measurement

Saturation flow rate is the maximum discharge rate during green time. The procedure for measuring saturation flow is summarized below. • The observation point is normally stop line (desired position to stop). Start of the green

was noted down from video camera timer. • Video camera gives time with accuracy of one minute. Lap timer was used to measure

time in seconds. The period of saturation flow begins when the green has been displayed for 3 seconds.

• Saturation flow ends when the rear axle of the last vehicle from a queue crosses the stop line. Initial 3 seconds from the start of green are left to take into account start up loss time.

On the dicsharge headway, when the signal turns green, the queue begins to move into the intersection. According to HCM 2000 calculation of the minimum discharge headway is typically accomplished by averaging the headways of those quesue positions that are relatively constant. In this regard HCM suggest that a constant headway is reached by the fifth queue position. Thus, minimum discharge headway is calculated by averaging headways for the fifth and subsequent position.

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Traffic stream at signalized intersection do stop periodically. When the traffic stream starts, the first several vehicles consume more than h sec/veh. Thus sum of the incremental headways (above h sec/v) for first several vehicles is called start-up lost time.

( )N

s ni

K h H= −∑

Where Ks= start up lost time (sec), hn= headway of the nth queue vehicle (sec), H=minimum discharge headway, N=number of queue positions having headways larger than H

3.0 INTERSECTION GEOMETRY AND POSSIBLE CONFLICTING POINTS

The site is a four-leg intersection. Clementi Ave 6 approach legs are four lane roadways and Commonwealth Ave approach legs are 8 lanes. All approaches are controlled with a traffic signal. The median of Clementi Ave 6 is approximately 10 meters which dedicated for tunnel road. The each approach lane widths are generally 3.3 meters wide. Details on the intersection geometry is shown in Appendix I. There is possibility conflict in existing intersection. Although intersection crashes are statistically rare events. However, in this exercise I would like to elaborate possibility conflict to measure the safety of intersection where would be usefule to optimize signal design.

Primary Conflict

Secondary Conflict

Vehicle Stream

Pedestrian Stream

Figure 1. Possible conflict points on existing intersection

One of the observational methods of determining the possible danger of an intersection configuration is to examine the number of conflict points. By definition, a conflict point is any point where a vehicle path crosses, merges, or diverges from another vehicle or pedestrian path. As can be seen in Figure 1, a standard 4-leg intersection has possibility 14 primary and 6 secondary conflict points. However, due to the insufficient video data of number of observed conflicts, therefore conflict conclusions could not be made.

Clementi Ave 6

Com

mon

wealth

Ave

Com

monw

ealth Ave

Angle camera N

W E

S

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4.0 INTERSECTION FLOW CHARACTERISTIC ANALYSIS

Initial examination of the minimum discharge headway, saturation flow and start up lost time is useful for initial analysis before proceed to signal design analysis by SIDRA. The results of this initial examination are helpful in that they present minimum headway, saturation flow rate and start up lost time in a form that is comparable with other works using the widely adopted calculation procedure described in the HCM 2000. However since the angle video were not captured all legs, therefore some headway data have been adjusted for some lanes in order to give better representation of actual condition.

Table 1 Minimum and average discharge headway and saturation flow rate

Movement type & location

Left Turn Through Right Turn H

(min) H

(ave) Std qs H (min)

H (ave) Std qs H

(min) H

(ave) Std qs

Cle Ave 6 (S) 1.09 2.19 0.57 1,642 1.12 2.12 0.50 1,698 1.03 1.94 0.58 1,855 Cle Ave 6 (N) 0.70 1.97 0.83 1,827 1.37 2.08 0.99 1,727 0.82 2.03 0.66 1,773 Com W (E) 0.54 2.07 1.25 1,732 0.49 1.96 0.97 1,836 1.28 2.27 0.93 1,585 Com W (W) 1.29 1.96 0.62 1,834 1.19 1.98 0.70 1,818 0.28 1.87 0.74 1,925 Summary 0.91 2.05 0.82 1,758 1.05 2.04 0.80 1,770 0.86 2.03 0.73 1,784 Notes: H(min) & (ave): Minimum and average discharge headway based on 2000 HCM procedure (i.e., the

average of all observed headway for the fifth through last queue positions), sec/veh. Data only consider passenger car arrival times (heavy behicle were excluded)

Std : Standard deviation, sec/veh qs : Saturation flow rate (3600/H(ave))

Table 2 Start up lost time for the basic movement type

Movement type Left Turn Through Right Turn Location Ks Std Ks Std Ks Std Cle Ave 6 (S) 2.41 1.37 2.49 1.24 2.87 1.72 Cle Ave 6 (N) 2.23 1.58 3.39 1.27 3.37 2.09 Com W (E) 3.28 2.08 3.23 1.60 2.71 1.90 Com W (W) 2.61 1.86 3.27 1.60 3.58 1.29 Summary 2.63 1.72 3.09 1.43 3.13 1.75

Notes: Ks : Start up lost time (based on the fourth queue vehicle time of arrival at the stop line. Data only

consider passenger car arrival times (heavy behicle were excluded) Std : Standard deviation, sec/veh From the above tables we can conclude that basic saturation flow for each movement are 1758 for LT, 1770 for T and 1784 for RT. Start up lost time for each turning movement are generally 3 second.

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5.0 SIDRA ANALYSIS

In this exercise we will use of the SIDRA (version 5.0) which allowed to analyse intersections under a number of varying traffic flow and control conditions to achieve optimal signal design. SIDRA was installed to operate on the HCM methodology with vehicles driving on the left. Queue lengths were calculated using a vehicle length of 4.5 m for LV and 10 m for HV. While SIDRA can provide a number of output measures, only those output values relating to this exercises are included in this report. Thus, flow characteristic shown in the above table 1 and 2 are input data for SIDRA default. Details on the input data are shown in the Appendix II. Start up lost time as input data for measuring effective green time. In this regard, since the number imput in SIDRA is integer, all the lost time data is rounded up or down following integer number. Set of phasing and signal timing is done by the Optimum Cycle Time option. Before we proceed the signal analysis, we proposed 2 alternatives of signal design. Followings are the alternative parameters at these intersections:

Alternative 1 (Do Nothing) Alternative 2 (Do Something) Signal cycle

• Minimum cycle length=60 seconds • Maximum cycle length=120 seconds

Signal cycle • Minimum cycle length=60 seconds • Maximum cycle length=150 seconds

Phase plan (4 phase) • 1st phase: main street through traffic

in both directions with permissive right turn (Commonwealth Ave)

• 2nd phase: protective right turn from both directions in main street (Commonwealth Ave)

• 3rd phase: side street through traffic in both directions with permissive right turn (Clementi Ave 6)

• 4th phase: protective right turn from both directions in side street (Clementi Ave 6)

Phase plan (2 phase) • 1st phase: side street through traffic in

both directions with permissive right turn (Clementi Ave 6)

• 2nd phase: main street through traffic in both directions with permissive right turn (Commonwealth Ave)

Phase timing • Minimum green=8 seconds, or for

pedestrian clearance whichever is greater

• Maximum green=80 seconds • Amber time=3 second • All-red time=2 seconds

Phase timing • Minimum green=6 seconds, or for

pedestrian clearance whichever is greater

• Maximum green=60 seconds • Amber time=3 second • All-red time=2 seconds

Details on the each phase plan of intersection are shown in the Appendix III.

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5.1 Alternative 1 (Do Nothing)

Do nothing alternative is existing phase movement based on own field survey (re-observation) at the site. Re-observation is conduct due to limitation view angle of video data. Phase movement was record during peak hour period similar to the video. Following table give the result of existing phase.

Table 3 Land use and performance of Alternative 1 Lane Use and Performance Demand Flows HV Cap. Deg.

Satn Lane

Util. Average

Delay Level of

Service 95% Back of

Queue Lane

Length L T R Total Vehicles Distance

veh/h veh/h veh/h veh/h % veh/h v/c % sec veh m m Lane 1 905 0 0 905 3.9 905 1 1.000 3 100 16.9 8 LOS B 8 25.5 8 184.4 8 100 Lane 2 18 0 93 0 111 0.0 681 0.163 100 21.2 LOS C 4.8 34.1 500 Lane 3 0 0 379 379 4.6 365 1.039 100 113.1 LOS F 32.0 233.1 500 Lane 4 0 0 379 379 4.6 365 1.039 100 113.1 LOS F 32.0 233.1 500 Approach 923 93 759 1775 4.0 1.039 58.3 LOS E 32.0 233.1 East: Commonwealth Ave West Lane 1 401 0 0 401 3.9 401 1 1.000 3 100 15.0 8 LOS B 8 9.6 8 69.6 8 35 Lane 2 523 0 0 0 523 3.5 410 1.274 100 308.4 LOS F 77.3 558.7 500 Lane 3 0 365 0 365 3.5 433 0.844 66 5 46.3 LOS D 20.2 145.7 500 Lane 4 0 0 17 17 0.0 181 0.096 100 50.1 LOS D 1.2 8.5 500 Lane 5 0 0 17 17 0.0 181 0.096 100 50.1 LOS D 1.2 8.5 500 Approach 923 365 35 1323 3.7 1.274 140.4 LOS F 77.3 558.7 North: Clementi Avenue 6 Lane 1 434 0 0 434 3.9 434 1 1.000 3 100 19.5 8 LOS B 8 12.9 8 93.4 8 50 Lane 2 489 0 365 0 855 3.5 654 1.306 100 332.7 LOS F 134.4 970.7 500 Lane 3 0 0 35 35 0.0 595 0.058 100 22.5 LOS C 1.4 9.7 500 Approach 923 365 35 1323 3.7 1.306 221.9 LOS F 134.4 970.7 West: Commonwealth Ave West Lane 1 827 0 0 827 3.9 827 1 1.000 3 100 10.8 8 LOS B 8 9.6 8 69.6 8 35 Lane 2 96 0 345 0 441 17.5 400 1.102 100 161.7 LOS F 45.7 359.5 500 Lane 3 0 438 0 438 17.5 397 1.102 100 161.8 LOS F 45.4 365.3 500 Lane 4 0 0 181 181 13.6 182 0.994 100 94.4 LOS F 13.7 106.9 500 Lane 5 0 0 181 181 13.6 182 0.994 100 94.4 LOS F 13.7 106.9 500 Approach 923 783 362 2068 10.7 1.102 89.6 LOS F 45.7 365.3 Intersection 6489 6.0 1.306 118.4 LOS F 134.4 970.7 Level of Service (Aver. Int. Delay): LOS F. Based on average delay for all lanes. LOS Method: Delay (HCM). Level of Service (Worst Lane): LOS F. LOS Method for individual lanes: Delay (HCM). Approach LOS values are based on average delay for all lanes.

95th percentile queue The 95 percentile queue represents the bounds of the queue at the intersection. The 95 percentile queue values are shown with regard to the amount of entering traffic in Table 3. It is shows that the worst length of queue are found at Lane 2 of Clementi Ave 6. Average vehicle delay The average intersection delay represents the total vehicle delay for the hour divided by the number of entering vehicles. The SIDRA output values for the average vehicle delay shows that average vehicle delay for all lane is 118 vehicle per second.

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Degree of saturation The degree of saturation is the amount of the intersection capacity that is being used by the stated traffic level. Degree of saturation is commonly referred to as the volume to capacity (v/c) ratio. The degree of saturation values were found not optimize at the existing condition where greater than 1. In summary, all results shown in the table are not met the criteria to be considered as optimal traffic condition where the Level of Service in this design is F. At the traffic levels studies here, it becomes a choice of the intersection control designer whether to provide lower overall delay while penalizing one or more approaches with higher delays or to minimize the worst approach delay Degree of saturation is also highest under these intersection traffic control design. Therefore, it can be concluded that existing traffic control design do not provide intersection better capacity for all approaches.

5.2 Alternative 2 (Do Something)

Alternative 2 is consider as alternative to optimize existing traffic signal design. In this regard, do-something alternative try to proposed better option to achieve better result. Following table are summarized of do-something alternative.

Table 4 Land use and performance of Alternative 2 Lane Use and Performance Demand Flows HV Cap. Deg.

Satn Lane

Util. Average

Delay Level of

Service 95% Back of

Queue Lane

Length L T R Total Vehicles Distance

veh/h veh/h veh/h veh/h % veh/h v/c % sec veh m m South: Clementi Avenue 6 Lane 1 923 0 0 923 3.9 931 1 0.992 100 19.7 8 LOS B 8 23.3 8 168.4 8 100 Lane 2 0 93 0 93 0.0 944 0.098 100 11.0 LOS B 2.9 20.3 500 Lane 3 0 0 379 379 4.6 388 0.979 100 86.1 LOS F 27.5 200.3 500 Lane 4 0 0 379 379 4.6 388 0.979 100 86.1 LOS F 27.5 200.3 500 Approach 923 93 759 1775 4.0 0.992 47.6 LOS D 27.5 200.3 East: Commonwealth Ave West Lane 1 455 0 0 455 3.9 455 1 1.000 3 100 14.0 8 LOS B 8 9.6 8 69.7 8 35 Lane 2 468 0 0 0 468 3.5 547 0.856 100 39.4 LOS D 23.4 168.9 500 Lane 3 0 365 0 365 3.5 577 0.633 74 5 27.6 LOS C 15.1 108.9 500 Lane 4 0 0 17 17 0.0 117 0.148 100 50.2 LOS D 1.2 8.1 500 Lane 5 0 0 17 17 0.0 117 0.148 100 50.2 LOS D 1.2 8.1 500 Approach 923 365 35 1323 3.7 1.000 27.7 LOS C 23.4 168.9 North: Clementi Avenue 6 Lane 1 513 0 0 513 3.9 513 1 1.000 3 100 21.0 8 LOS C 8 12.9 8 93.1 8 50 Lane 2 411 0 365 0 776 3.5 897 0.865 100 28.3 LOS C 35.2 254.4 500 Lane 3 0 0 35 35 0.0 691 0.050 100 19.2 LOS B 1.2 8.2 500 Approach 923 365 35 1323 3.7 1.000 25.2 LOS C 35.2 254.4 West: Commonwealth Ave West Lane 1 855 0 0 855 3.9 855 1 1.000 3 100 10.6 8 LOS B 8 9.6 8 69.7 8 35 Lane 2 68 0 358 0 427 17.5 532 0.802 100 34.4 LOS C 19.9 157.6 500 Lane 3 0 425 0 425 17.5 530 0.802 100 34.4 LOS C 19.8 159.6 500 Lane 4 0 0 181 181 13.6 184 0.986 100 91.2 LOS F 13.8 107.6 500 Lane 5 0 0 181 181 13.6 184 0.986 100 91.2 LOS F 13.8 107.6 500 Approach 923 783 362 2068 10.7 1.000 34.5 LOS C 19.9 159.6 Intersection 6489 6.0 1.000 34.8 LOS C 35.2 254.4

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Level of Service (Aver. Int. Delay): LOS C. Based on average delay for all lanes. LOS Method: Delay (HCM). Level of Service (Worst Lane): LOS F. LOS Method for individual lanes: Delay (HCM). Approach LOS values are based on average delay for all lanes.

95th percentile queue The 95 percentile queue represents the bounds of the queue at the intersection. The 95 percentile queue values are shown with regard to the amount of entering traffic in Table 4. After do something on existing signal design, the alternative shows better length of queue in comparison with existing design. Average vehicle delay The average intersection delay represents the total vehicle delay for the hour divided by the number of entering vehicles. The SIDRA output values for the do something alternative shows that average vehicle delay for all lane is improve to 35 vehicle per second. Degree of saturation The degree of saturation is the amount of the intersection capacity that is being used by the stated traffic level. Degree of saturation is commonly referred to as the volume to capacity (v/c) ratio. The degree of saturation values were found improving after change the phase movement. This phase optimize existing condition where the results is 1 in average. In summary, all results shown in the table are improve and the phase movement could be considered as optimal traffic condition where the Level of Service in this design is C. Degree of saturation is also better under these intersection traffic control design. Therefore, it can be concluded that alternative 2 traffic control design has provide intersection better capacity for all approaches.

6.0 CONCLUSION

From the results of this exercise the following conclusions are drawn. • The exisiting signal design of the Commonwealth intersection do not met LOS criteria in

optimal condition. There was an average delay of 118 vehicle per hour and degree of saturation of greater than 1.

• The existing intersection was found to experience a higher level of 95th percentile back of the queue with 134 vehicle in the distance 971 m.

• The do something scenario operated better performance than the existing signal design. Comparable of these alternatives is shown with improvement in regard to degree of saturation (v/c ratio).

However, all parameters of intersection flow for further work should calibrate and validate in order to achieve better results and drawn an existing condition. It is also need to analyse length cycle determination and critical movement in each lane movement. Therefore an better improvement could be made.

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REFERENCES

Highway Capacity Manual. 2000. Special Report 209, 4th Ed., TRB, National Research Council, Washington, D.C.,

May, A. D. (1990), Traffic Flow Fundamentals, Prentice-Hall, Inc., Englewood Cliffs, N.J.

Bonneson, J A. (1993), Study of Headway and Lost Time at Single-Point Urban Interchanges. Transportation Research Record No: 1365. Transportation Research Board

Traffic Monitoring Guide, 3rd Ed. Federal Highway Administration (FHWA)

Traffic Flow Theory A State-of-the-Art Report (2001). Committee on Traffic Flow Theory and Characteristics (AHB45). TRB, National Research Council, Washington, D.C.,

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APPENDIX I ROAD GEOMETRY

APPENDIX II VOLUME INPUT

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APPENDIX III

Phasing Summary Alternatives 1

Cycle Time Option: Optimum Cycle Time (Minimum Delay) Phase times determined by the program Green Split Priority for Coordinated Movements specified Sequence: Two-Phase Input Sequence: A, B, C, D Output Sequence: A, B, C, D Phase Timing Results Phase A B C D Green Time (sec) 25 6 39 6 Yellow Time (sec) 4 4 4 4 All-Red Time (sec) 2 2 2 2 Phase Time (sec) 31 12 45 12 Phase Split 31 % 12 % 45 % 12 %

Phasing Summary Alternatives 2

Cycle Time Option: Optimum Cycle Time (Minimum Delay) Phase times determined by the program Green Split Priority for Coordinated Movements specified Sequence: Two-Phase Input Sequence: A, B Output Sequence: A, B Phase Timing Results Phase A B Green Time (sec) 48 30 Yellow Time (sec) 4 4 All-Red Time (sec) 2 2 Phase Time (sec) 54 36 Phase Split 60 % 40 %

Exercise 5 - Traffic Signal Design Aditya Nugroho e

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