The observed relatively strong hyperbolic

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Unformatted text preview: simulated using the transporter module of ARENA. The transporter module of ARENA allows the programmer to enter the speed distribution for the vehicles. The inter-arrival times of the entities (vehicles) entering the construction work zones were determined according to the field data collected. The vehicle type assignment (i.e. car or truck) along with the lengths were made at the point of entry. The vehicles were represented with the entity-transporter pairs in the system. When the vehicles entered the system, the speed distribution functions were assigned to the vehicles using transporters. Another important issue in traffic simulation was the headway and the spacing between the vehicles. Headway is defined as the time between successive vehicles as they pass a point on a lane or roadway, using a common reference point on both vehicles and spacing is defined as the distance between successive vehicles in a traffic stream, as measured from front bumper to front bumper [23]. In order to specify the headways and spacing between the vehicles, initially, the headway and spacing were determined according to the arrival time of the vehicles. The difference in vehicle arrival times 52 determined the headways and spacing. Additional length was added to the length of the vehicles to maintain the minimum spacing during simulation. The travel time (delay time) in the work zone was determined according to the speed profiles of the vehicles in the work zone. The model was evaluated using the data collected in the field. The use of real world data allowed us to compare the outputs of the model and to analyze the accuracy of its outputs. About 1750 statements were used in the program to model traffic. Most of the modules used at the stations for lane changing behavior were used with small changes in the statements. One simulation run (replication) took about 30 minutes on a PC with 2.8 GHz processor and 1.0 GB RAM. 3.2.2 Design of the ARENA Traffic Simulation Model 3.2.2.1 Input Variables The traffic data was entered into ARENA simulation program by using number of variables which defined the system. According to these input variables the program computed the output variables. The following variables were entered in order to get the output variables. 3.2.2.1.1 Construction Zone Configuration The model was developed for two lane traffic configuration. Construction work was performed on the passing lane of the road and the passing lane was closed for 5600 feet. The map of the construction zone is given in Figure 1. Vehicles were simulated 53 beginning from 700 feet in advance of the first “Left Lane Closed Ahead” sign. Then the second and third lane closure signs were placed 1200 feet and 1700 feet after the beginning of the simulation. After 500 feet from the third left lane closure sign, the lane closure taper was begun. The length of the lane closure taper was 150 feet. One lane road (after the left lane merge) shifted to the shoulder at 2300 feet with 300 feet taper. After the merging of left lane and shifting of right lane to the shoulder, one lane road in construction zone was simulated for 350 feet. After 3000 feet from the beginning of the simulation start point, vehicles left the system. The dimensioning and the placement of the traffic signs and drums are given in Figure 13. 3 2 1 1. First “Left Lane Closed Ahead” Sign 2.Second “Left Lane Closed Ahead” Sign 3.Third “Left Lane Closed Ahead” Sign Figure 13: Work Zone Configuration used in the Example Simulation 54 The construction zone in ARENA simulation program was modeled by using the intersections and links elements of the program [26]. Intersections were defined at the changes in the construction zone. And the links defined the distances between the intersections. These two elements defined the network system in the simulation. Originally the system was simulated for 14000 feet. It was starting 7950 feet before the left lane closure taper and ending 6050 feet after the taper. The simulation run length using the original distances took 3 – 5 hours for 1 replication. In order to decrease the simulation runtime, the distances for the construction zone were reduced. The reduction of the distances would not cause any loss of data, since the objective of the model was to identify the queue length and the waiting time at the lane closure taper. 3.2.2.1.2 Inter-arrival Time Distribution (Entity Arrival) Vehicle entry to the system was modeled using the create module of ARENA simulation program. Actual inter-arrival times of the vehicles at the beginning of the work zone were collected in the field. As mentioned earlier in section 3.1.3.1 [page 26] the inter-arrival times of the vehicles were analyzed and a spreadsheet for determining the cumulative percentages of inter-arrival times for given hourly traffic counts was established. Using the spreadsheet, inter-arrival times of vehicles for 24- hour time period for a weekday were determined using the actual count data from 08/20/2004 Friday. Hourly vehicle counts...
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This document was uploaded on 02/26/2014 for the course E 515 at University of Louisiana at Lafayette.

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