Evaluating Traffic Operation for Multilane Highway (Ramadi (cid:150) Fallujah) Highway as Case Study

Multilane highways typically are located in suburban communities, leading into central cities, or along high-volume rural corridors connecting two cities or significant activities that generate a substantial number of daily trips. The objectives of the present study include the analysis, and evaluation the level of service (LOS) on section for multilane highway in Ramadi city. The LOS multilane highway is based on density, which is calculated by dividing per lane flow by speed. The required traffic and geometrical data has been collected through field surveys on the section for multilane highway. Traffic volume data were collected manually and classified by vehicles types during each 15 minute interval. Highway Capacity Software 2000 (HCS 2000) program is used for the requirements of traffic analysis process to determine the level of service. It has concluded that the level of service on selected section for east bound is (A), and for west bound is (B).


Introduction
Increasing traffic flow has forced engineers to increase the number of lanes of highways in order to provide good maneuvering facilities to the users. A highway is a public road especially a major road connecting two or more destinations (Khistyand Lall, 2003). A highway with at least two lanes for the exclusive use of traffic in each direction, with no control or partial control of access, but that may have periodic interruption to flow at signalized intersections not closer than 3km is called multilane highway (Abdullah, 2005).Multilane highways exist in a number of setting, from typical suburban communities leading to central cities or along high-volume rural corridors that connect two cities or significant activities generating a substantial number of daily trips. Multilane highways range from the uninterrupted flow of freeways to the flow conditions on urban streets, which are frequently interrupted by signals. The capacity of a multilane highway is the maximum sustained hourly flow rate at which vehicles reasonably can be expected to traverse a uniform segment under prevailing roadway and traffic conditions (Al-Sughaiyer, 2005). They generally have posted speed limits of between 60 km/h and 90 km/h. They usually have for or six lanes, often with physical medians or two-way right turn lane (TWRTL), although they may also be undivided (Abdullah, 2005). The traffic volumes generally varies from 1500-40000 per day. It may also vary up to 100000 per day with grade separations and no cross-median access. Traffic signals at major intersections are possible for multilane highways, partial control access (Abdullah, 2005).
The main objectives of this study is to analyze level of service (LOS) which is very important issue for traffic engineer because it describes the traffic operational conditions within a traffic stream. Also we are going to study the characteristics and capacity for multilane highways. Free-flow speed (FFS) is a parameter that is being used extensively for capacity and level of service analysis of various types of highway facilities.

Methodology
The methodology described in this study is intended for analysis of uninterrupted-flow highway segments. Figure (1) shows the inputs and basic computational order for the method described in this study. The primary output is level of service.

Level of Service for Multilane Highway
Basically any two of the following three performance characteristics can describe the level of service for a multilane highway (Khistyand Lall, 2003, Abdullah, 2005.: 1-Volume to capacity ratio. 2-Speed, in terms of mean passenger cars speed, and, 3-Density, in terms of passenger cars per kilometre per lane. Each of these measures indicates how well the highway accommodates traffic flow. As speed does not vary over a wide range of flow, it is not a good indicator of service quality. Density which is a measure of proximity of other vehicles in the traffic stream is directly perceived.

Procedures to Determine Level of Service
The prediction of level of service for multilane highway involves three steps: 1-determine of free-flow speed. 2-determine of flow rate. 3-determine of level of service.

Determination of Free-Flow Speed
Free-flow speed is the theoretical speed of traffic density approaches zero. It is the speed at which drivers fell comfortable traveling under physical, environmental, and traffic conditions existing on an uncongested section of multilane highway (Abdullah, 2005).Free-flow speed is measured using the mean speed of passenger cars operating in low to moderate flow condition ( up to 1400 pc/h/ln). Mean speed is virtually constant across this range of flow rates (Highway Capacity Manual 2000). If the speed study must be conducted at a flow rate of more than 1400 pc/h/ln, the free-flow speed can be found by using the model speed-flow curves assuming that data on traffic volumes are recorded at the same time (Highway Capacity Manual 2000).
The maximum sustained hourly flow rate, which forms the basis for defining capacity, is considered a function of density and therefore speeds. Because free-flow speed is a direct input to the density computation, adjustments for geometric factors are applied to free-flow speed. Several traffic control, physical, and traffic conditions affect the free-flow speed along a given highway. If speed enforcement is common, it can be anticipated that traffic operation will often be affected. Under those circumstances, the user may make local measurements to calibrate the relationship between the 85th-percentile speed and the free-flow speed. Design speed and posted speed limits may also impact free-flow speed. Level of service criteria for multilane highways are defined in terms of density. These LOS boundaries are represented in Figure (2) by slope lines, each corresponding to a constant value of density. Complete LOS criteria are given in Table (1). For average free-flow speed 70,80,90,and 100 km/h, the Table gives the average travel speed, the maximum service flow (MSF) rate for each level of service. Under base conditions, the speeds, v/c ratios, and tabulated MSF are expected to exist in traffic streams operating at the densities defined for each level of service. The average passenger car speed under low-volume conditions can be used directly as the free-flow speed if the field measurements were made at flow rates at or below 1400 pc/h/ln. If field-measured data are used, no adjustments need to be made to free-flow speed. Thisfree flow speed reflects the net effects of all conditions at the site that influence speed, including those identified in this procedures ( lane width, lateral clearance, type of median and access points ), as well as others, such as speed limit and vertical and horizontal alignment (Highway Capacity Manual 2000). Recent research suggests that free-flow speed on multilane highways under base conditions is approximately 11 km/h higher than the speed limit for 65 km/h to 70 km/h speed limits, and it is 8 km/h higher for 80 km/h to 90 km/h speed limits (Highway Capacity Manual, 2000).

Determination of Flow Rate
Two adjustments must be made to hourly volume counts or estimates to arrive at the equivalent passenger-car flow rate used in LOS analyses. These adjustments are the PHF and the heavy-vehicle adjustment factor. The number of lanes also is used so that the flow rate can be expressed on a per-lane basis. These adjustments are applied as follows(Highway Capacity Manual 2000): (1) Where: V p = 15-min passenger-car equivalent flow rate (pc/h/ln), V= hourly volume (veh./h), PHF= peak-hour factor, N= number of lanes, f HV = heavy-vehicle adjustment factor, and f p = driver population factor. PHF represents the variation in traffic flow within an hour. Observations of traffic flow consistently indicate that the flow rates found in the peak 15-min period within an hour are not sustained throughout the entire hour. The PHFs for multilane highways have been observed to range from 0.75 to 0.95. Lower values are typical of rural or off-peak conditions, whereas higher factors are typical of urban and suburban peak-hour conditions. Besides that, the presence of heavy vehicles in the traffic stream decrease the free-flow speed because base conditions allow a traffic stream of passenger cars only. Therefore, traffic volumes must be adjusted to reflect an equivalent flow rate expressed in passenger cars per hour per lane (pc/h/ln). This is accomplished by applying the heavy-vehicle factor (f HV ). Once values for ET and ER have been determined, the adjustment factor for heavy vehicles may be computed as shown in Equation (2).
( 2) where: ET,ER= passenger-car equivalents for trucks and buses and for recreational vehicles ( RVs), respectively, PT,PR= proportion of trucks and buses, and RVs, respectively, in the traffic stream ( expressed as a decimal fraction ), and f HV = adjustment factor for heavy vehicles.
Adjustment for heavy vehicles in the traffic stream applies to three types of vehicles : trucks, RVs, and buses. No evidence indicates any distinct difference in the performance characteristics of trucks, and buses on multilane highways; therefore, buses are considered trucks in this method. Finding the heavy-vehicles adjustment factor requires two steps. First, find an equivalent truck factor (ET) and RV factor (ER) for prevailing operating conditions. Second, using ET and ER, compute an adjustment factor for all heavy vehicles in traffic stream. Table (2) is used to select passenger-car equivalents for trucks and buses (ET) and for RVs (ER).

Table 2.Passenger-car equivalents on extended general highway segment[3]
Type of Terrain Factor Level Rolling Mountainous ET (trucks and buses) 1.5 2.5 4.5 ER (RVs) 1.2 2.0 4.0 The adjustment factor fp reflects the effect weekend recreational and perhaps even midday drivers have on the facility. The values of fp range from 0.85 to 1.00. Typically, a value of 1.00 can be selected unless there is sufficient evidence to apply a lesser value to reflect recreational traffic characteristics[3].

Determination Level of Service (LOS)
The LOS on a multilane highway can be determined directly from Figure (2) on the basis of the FFS and the service flow rate (vp) in pc/h/ln. The procedure is as follows: • Step 1. Define and segment the highway as appropriate.
• Step 2. On the basis of the measured or estimated FFS, construct an appropriatespeed-flow curve of the same shape as the typical curves shown in Figure ( Where: D= density (pc/km/ln), V P = flow rate (pc/hr/ln), and S= average passenger-car travel speed (km/hr). The LOS also can be determined by comparing the computed density with thedensity ranges provided in Table (1).

Road Section Condition
The road section is about 4km, located in Ramadi city. The road is respected a multilane where it has two lanes in each direction. The road width is 7 m in each direction, flexible pavement, and divided by median. There are many of houses, schools, and service facilities along both the side of road section and many access branches. The terrain of road section is level. Figure (3) shows a satellite image for multilane highway in Ramadi city.

HCS Multilane Highways
Highway Capacity Software (HCS 2000) is a program based on the Highway Capacity Manual. It is primary function is to analyze capacity and provide level of service on multilane highway. HCS requires the following traffic inputs: number of lanes, lane width, lateral clearance, median (yes/no), access-point density, specific grade or general terrain, free-flow speed, traffic volume, length of analysis period, peak-hour factor, percentage of heavy vehicles, and driver population factor. HCS output is the level of service on multilane highway (Highway Design Manual, 1994).

Traffic Volume
The traffic account is carry out at multilane highway (Ramadi-Baghdad highway) for two directions from 7:00 am to 5:00 pm during the work day of the week on January month in 2012 and the highest recording traffic volume in each direction is recorded to be used in the analysis of the present study. The vehicles are classified into two types: 1-Small vehicles: any vehicles move on four wheels includes the passenger cars. 2-Large vehicles: any vehicles move on more than four wheels includes buses and trucks (heavy vehicles). This type of vehicle is converted to passenger car by using passenger car unit (PCU) factor equal to 1.5 according to Table (2).Tables (3 and 4) appear the highest account traffic volume in each direction for every 15 min. and Table (5) shows the traffic volume for every one hour from 7:00 am to 5:00 pm.

Analysis and Results
Highway Capacity Software (HCS) program was applied in this study for requirements of evaluating and analyzing the multilane highway, the following parameters were calculated: 1-Traffic volume adjustment. 2-Free flow speed (FFS). 3-Level of service (LOS).

Calculating of Peak Hour Factor (PHF)
The peak hour factor is defined as the ratio of total hourly volume to the maximum 15min. rate of flow within the hour as following Equation: (4) Where: PHF= Peak-hour factor V 15min. = Volume during the peak 15 min of the peak hour, on veh/15min The peak hour factor is calculated for each direction of multilane highway by using the data mentioned in Tables (3 and 4 ). Results of PHF is shown in Table (8).

Field Measured of Free Flow Speed
Free flow speed is measured for both direction depending on spot speed studies, where the free flow speed is the average speed as shown in Table (9) and figures (6 and 7).