Evaluation The Performance of Al-Thawra At-Grade Intersection Using The HCS2000 Computer Package

Al-Thawra signalized intersection is one of the most important intersections in AL-Hilla city because it relates the Governorates: Baghdad, Najaf, Kerbala and Babel, and serves of about 21000000 passages of ve hicles ye arly. The excessive tr affic volumes, during the peak periods (at morning and evening), of vehicles that entering the intersection increase t raffic density, reduce travel speed, increase travel ti me, and increase the delay values. The delay values are reflected by McTrans Center, University of Florida {Highway Capacity Ma nual (HCM2000)} to an indicator named LEVEL OF SERVICE (LOS). The operational analysis of the existing conditions of this intersection by the Highway Capacity Software (HCS2000) indicates that the LOS of it equal to (F) with an intersection delay value of 263.7 sec./vehicle and a degree of saturation exceeds 1.5. Therefore, and be cause of the rea sons above, it is important to im prove the performance of Al-Thawra Interse ction by separate the c onflicting traffic movements with an overpass bridge. The traffic survey shows that the high traffic volume of through movement of t he N orth-South direction ( Baghdad-60St.) ha s the ma jor effect on the intersection. T herefore, the North-South is the suitable direction to co nstruct the suggested bridge overpass to separate the through traffic of this direction (from Baghdad to Najaf { 60 St.} an d vice ve rsa) from the ot her movements of the intersection. The results indicate that the intersection LOS equal ( C ) with a cycle time of ( 58 ) sec. and an intersection delay of ( 22.8 ) (sec./veh.) at the object year 2027


1-Introduction:
Al-Thawra signalized intersection is one of the most important intersections in AL-Hilla city because it relates the Several Governorates: Baghdad, Najaf, Kerbala and Babel, as shown in Figure ( 1), and serves of about 21000000 passages of vehicles yearly.
The excessive traffic volumes, during the peak periods (at morning and evening), of vehicles that entering the intersection increase traffic density, reduce travel speed, increase travel time, and increase the delay values.The delay values are reflected by McTrans Center, University of Florida {Highway Capacity Manual (HCM2000)} to an indicator named LEVEL OF SERVICE (LOS).The operational analysis of the existing conditions of this intersection by the Highway Capacity Software (HCS2000) indicates that the LOS of it equal to (F) with an intersection delay value of 263.7 sec./vehicle and a degree of saturation exceeds 1.5.Therefore, and because of the reasons above, it is important to improve the performance of Al-Thawra Intersection.
To study and evaluate the existing conditions in the intersection, the following items are required: a) Data collection of the existing traffic volumes for each approach (Left, Through, and Right) within the intersection.b) From the above traffic volume data, the peak (15 min.)volume, as well as, the peak hour factor can be obtained.c) Determination of the existing LOS, under existing conditions of geometry and traffic operation, by using HCS2000 program.d) Estimation of traffic volume at the designed year ( 2027).e) Proposed suitable solutions that may be improved the performance of the intersection depending on the traffic volumes and movements and the availability of free spaces.f) Evaluation of the suggested proposals under the estimated traffic volumes at the object year 2027.

2-Data Collection:
To determine the existing traffic volumes of Al-Thawra intersection, a digital camera is used.The peak hour periods (morning and evening) is then found at 8:00-9:00 morning and 1:00-2:00 evening.The traffic volumes are collected at 25/6/2007 for each approach, as well as, for each movement from the movie and tabulated in Table (1) below.
From the data of In the same way, from the traffic counts, it can be seen that the through traffic volume in the North-South direction (Baghdad-Najaf 60St.) is the highly traffic volume in the intersection.This means that the improvements should take this direction into PDF created with pdfFactory Pro trial version www.pdffactory.comconsiderations to improve the intersection performance.

3-Overview of the Highway Capacity Manual and Its Software:
The Highway Capacity Manual (HCM) provides transportation practitioners and researchers with a consistent system of techniques for the evaluation of the quality of service on highway and street facilities.The HCM does not set policies regarding a desirable or appropriate quality of service for various facilities, systems, regions, or circumstances.Chapter 16 of HCM2000 contains a methodology for analyzing the capacity and level of service (LOS) of signalized intersections.The analysis must consider a wide variety of prevailing conditions, including the amount and distribution of traffic movements, traffic composition, geometric characteristics, and details of intersection signalization.The methodology focuses on the determination of LOS for known or projected conditions.The methodology addresses the capacity, LOS, and other performance measures for lane groups and intersection approaches and the LOS for the intersection as a whole.Capacity is evaluated in terms of the ratio of demand flow rate to capacity (v/c ratio), whereas LOS is evaluated on the basis of control delay per vehicle (in seconds per vehicle).Control delay is the portion of the total delay attributed to traffic signal operation for signalized intersections.Control delay includes initial deceleration delay, queue move-up time, stopped delay, and final acceleration delay.Figure (2) shows the input and the basic computation order for the method.The primary output of the method is level of service (LOS).This methodology covers a wide range of operational configurations, including combinations of phase plans, lane utilization, and left-turn treatment alternatives.It is important to note that some of these configurations may be considered unacceptable by some operating agencies from a traffic safety point of view.The safety aspect of signalized intersections cannot be ignored, and the provision in this chapter of a capacity and LOS analysis methodology for a specific operational configuration does not imply an endorsement of the suitability for application of such a configuration.
The average control delay per vehicle is estimated for each lane group and aggregated for each approach and for the intersection as a whole.LOS is directly related to the control delay value.The criteria are listed in Table (2).On the other hand, Table (3) provides a summary of the input information required to conduct an operational analysis for signalized intersections.This information forms the basis for selecting computational values and procedures in the modules that follow.The data needed are detailed and varied and fall into three main categories: geometric, traffic, and signalization.The input worksheet is shown in Figure (3).

4-Description of the Selected Program (HCM2000):
Highway Capacity Software (HCS 2000)  Input Quick jump and report quick jump are pulldown lists from which to select.A specific place in the input or report screens to be positioned.Simply click on either field and select the portion of the input or report screens to move to and appropriate screen will position itself here.
Quick Entry takes the user to a graphic data entry screen as an alternate method for coding traffic volume and lane configuration data.In the Quick entry screen, the user first selects an approach from the EB (east bound), WB (west bound) NB (north bound) and SB (south bound) buttons in the lower right corner.Then the lane combination can be selected by clicking on appropriate arrows to place them on the central diagram next turning volumes ( left, thru and right )can be entered for the selected approach which will also be transferred to the central diagram, for an overall view of the intersection .These data are coordinated with the normal data entry screen so that changes in either view are reflected in the other.
Then the user codes the traffic volume for each movement of the intersection in vehicles per hour.An hourly volume is required for any movement to be included in the analysis.There is an optional globule spinner at the end of the traffic volume row that will allow the coded volumes to be incremented by the percentages hour in the all volume field using the adjacent spinner.This is especially useful when doing sensitivity analyses for various growth rates.Either peak Hour factor (PHF-peak 15-minute volume, Right turns on red , number of usage lane , Average Queue spacing (Lh), storage length (La) and Adjusted flow rate are entire.

* Operating Parameters
Either the arrival type or proportion arriving during green is coded to define the quality of progression.The arrival type is coded from 1 to 6 with being poor progression, 2 being unfavorable progression, 3 being random arrivals, 4 being favorable progression, 5being highly favorable progression and 6 being exception progression.Crosswalk length, pedestrian speed and crosswalk width are entered to calculate the minimum green in seconds required to accommodate pedestrian operations.

* Phasing
The phase design area is used to enter the inter section timing plan.Timing must be determined by external means, other programs or manual methods.HCS does not estimate timing.Phase design is coded using up to eight phase area to define combinations of movements and timing.Each distinct phase is defined by coding the green, yellow and red (all red) times in seconds with all movements allowed during each phase.

* Saturation Flow
The ideal saturation flow rate is coded for each lane group, and then adjusted by using the equation in HCM.S = So N Fw FHv Fg Fp Fbb Fa Flu Flt Frt Flpb Frpb PDF created with pdfFactory Pro trial version www.pdffactory.com Where: S= saturation flow rate for subjected lane group, expressed as a total for all lanes in lane group (veh/h).So= base saturation flow rate per lane (Pc/h/in).N= number of lanes.Fw= adjustment factor for lane width.FHv= adjustment factor for heavy vehicle in traffic stream.Fg= adjustment factor for approach grade.Fp= adjustment factor for existence of a parking lane and parking lane and parking activity adjacent to lane group.Fbb= adjustment factor for blocking effect of local buses that stop within intersection area.Fa= adjustment factor for area type.Flu= adjustment factor for lane utilization.Flt= adjustment factor for left turns in lane group.Frt= adjustment factor for right turns in lane group.Flpb= pedestrian adjustment factor for left-turn movement.Frpb= pedestrian.Bicycle adjustment factor for right turn movements.

* The Results
The Lane group capacity is computed for each lane group by multiplying the adjusted saturation flow rate by the g/c ratio.The lane group v/c ratio is calculated by dividing the adjusted flow rate by the lane group capacity.
The back of Queue is the number of vehicles that are queued depending on arrival patterns of vehicles and vehicles that do not clear the intersection during a given green phase.
The lane group delay is calculated as the sum of the uniform delay (d1) as adjusted by the progression factor (pf), incremental delay (d2) and initial Queue delay (d3).The lane group level of service is then determined from comparing the lane group delay with the thresholds defined in HCM Exhibit 16-2-Approach delay is calculated as the average delay for each lane group weighted by the lane group flow rate as defined in HCM equation 16-14 which is: The approach level of service is then determined from comparing the approach delay with the thresholds defined in HCM Exhibit 16-2.
Intersection delay is calculated as the average delay for each approach weighted by the lane group flow rate as defined in HCM equation 16-15.The intersection level of service is then determined from comparing the intersection delay with the thresholds defined in HCM Exhibit 16-2.

5-Some Traffic Improvement Studies:
Many traffic improvement studies were made in Iraq.Some of these studies used HCS program for evaluation process and providing the optimal single timing data.These are some of these studies: First example: the study that carried out by [AL-Arkwazze, 2003] in 14th-Ramadhan arterial street in Baghdad city.This arterial street consists of six signalized intersections, which suffer from high congestion level especially during (8:30-9:30) a.m peak period because of high traffic volumes and bad timing plan.Five improvements were suggested by [AL-Arkwazze, 2003] to decrease the congestion problem in the study area.
[Abdul-Ghani 2004] studied three important streets (AL-Rashid, AL-Khalafa and AL-Kifah) which are located in Central Business District area.The area of study consists of thirteen intersections.This area suffer from sever congestion conditions, especially at time between (10:00-12:00) a.m and (1:30-3:30) p.m. period because of many PDF created with pdfFactory Pro trial version www.pdffactory.comactivities.Centers such as government institutions, ministries so the aim of the study was to relieve the traffic problems by suggesting several alternatives.

6-Operational Analysis of the Existing Conditions:
The operational of the existing geometrical features and traffic volumes of Al-Thawra intersection is performed using HCS2000.Table (4) illustrates the results of analysis.The results indicate that the intersection LOS is (F) with an average intersection delay of 263.7 sec./vehicle.
Therefore, the improvements are required to reduce the intersection delay and change the LOS.

7-Proposal Improvement of Traffic Performance:
In order to improve the traffic performance in the study area, improvement proposals will be explained in the following section.

7-1 Proposal NO 1: Changing the cycle length for the intersection:
In this proposal, several cycle lengths are examined using HCS program.From the result, it is noticed that the (LOS) for the intersection is (F) ,therefore, the proposal is not good enough for the intersection.Table (5) shows the results for this proposal for the cycle time 168 sec.as example.The results are based on existing traffic volume observed at the selected signalized intersection.

7-2 Proposal NO 2: Increasing the number of lanes in each direction:
In this proposal, changing of geometric design for the intersection by increasing the number of lanes in each approach is suggested.It was found that the LOS of the intersection is still F with an overall delay of (200.6)sec/veh.

7-3 Proposal NO 3: Construct an overpass bridge:
The traffic survey shows that the high traffic volume of through movement of the North-South direction (Baghdad-60St.) has the major effect on the intersection.Therefore, the North-South is the suitable direction to construct the suggested bridge overpass to separate the through traffic of this direction (from Baghdad to Najaf {60 St.} and vice versa) from the other movements of the intersection.

Future Traffic Volume:
The geometric design of new highway facilities or improvements to existing highways should not usually be based on the current traffic volumes only, but should consider future traffic volumes that may uses the facility.Many highway designers believe the maximum design period is in the range of 15 to 24 years.Therefore, a design period of 20 years is widely used.The traffic flow within this period cannot usually be expected accurately because of the probable changes in the general regional economy, population, and land use and development around the facility, which cannot be predicted with any degree of assurance.With this preface, the selected design life for Al-Thawra Intersection is 20 years with an annual growth rate of 3% which reflects the socioeconomic nature of Babel city.The necessary calculation for the projection of the current traffic volumes to represent the future traffic in the design year 2027 is:  5) below.

The proposed Geometric Design:
After considering the future traffic volumes for the different movements in the intersection, the PDF created with pdfFactory Pro trial version www.pdffactory.comproposed geometric design can be seen in Figure ( 4).The design represents the unique solution to improve the performance of the intersection.
The proposed design is based on the concept of eliminating the heaviest through traffic volume from Baghdad to Najaf and vice versa.The proposed four lane overpass will accommodate the future traffic volume in this direction (North-South) with an acceptable LOS of (C).The use of traffic signals to control the traffic movements within the intersection with the aid of improvements (overpass) and channelizations will participate into large extent in intersection performance betterment and make operation of the intersection under an acceptable LOS at the design year (2027).
On the other hand, the suggested geometric design of the at-grade intersection is tabulated in Table ( 7) below.

Interchange Performance Analysis at 2007 & at the Design Year (2027):
The collected traffic volumes at 25/6/2007 are used to predict the interchange LOS after considering the proposed geometric design.Table (8) shows the HCS summarized results of averaged delay and LOS.
After considering the proposed geometric design, a new signal phasing plan with new signal timing is used to evaluate the intersection LOS under the predicted traffic demand at the year 2027 by HCS2000.The signal phasing plan is shown in Figure ( 5) and the summary of the results is given in Table (9).The results indicate that the intersection LOS equal (C) with a cycle time of ( 58) sec.and an intersection delay of ( 22.8) (sec./veh.).

8-Summary:
Al-Thawra signalized intersection is one of the most important intersections in AL-Hilla city because it relates the Governorates: Baghdad, Najaf, Kerbala and Babel, and serves of about 21000000 passages of vehicles yearly.
The operational analysis of the existing conditions of this intersection by the Highway Capacity Software (HCS2000) indicates that the LOS of it equal to (F) with an intersection delay value of 263.7 sec./vehicle and a degree of saturation exceeds 1.5.Therefore, and because of the reasons above, three improvement proposals were suggested.The study showed that an overpass over the heaviest traffic volume direction is the best solution to improve the intersection performance.The results indicated that the intersection measures of effectiveness at the goal year (2027) will be: -LOS = C -Intersection delay = 22.8 (sec./veh.)with an intersection cycle time = 58 (sec.).9-References: 1-Abdul -Ghani, M.M., ( 2004 PDF created with pdfFactory Pro trial version www.pdffactory.comPDF created with pdfFactory Pro trial version www.pdffactory.com future traffic volumes for the effective movements in Al-Thawra Intersection are tabulated in Table(

Table (
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Table ( 3) Continued. Type of condition Parameter
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