بررسي رفتار رانندگان در پذيرش فواصل عبوري قابل قبول بحراني درتقاطع هاي بدون چراغ راهنمايي در ايران و تاثير آن در ميزان تاخير اين تقاطعات به روش پيشنهادي hcm2000

Effect of Driversʹ Behavior in Capacity and Delay of Non signalized Intersections and Calibrating Delay Equations in HCM2000

Capacity and delay are two most important measures in the evaluation of non signalized intersectionʹs performance that have been widely used in traffic improvement projects and transportation network assignment models. Because of the close relation between driver behaviors and traffic regulations with the Investigation and computation of delay and capacity in non signalized intersections the analysis of these intersections are so sophisticated. The purpose of this research is to adapt the state of the art algorithm used in HCM 2000 with Iranʹs situation with respect to the gap acceptance behavior of the drivers in Iran. The data achieved from several field observations on the intersections of Tehran have been used to calibrate the gap acceptance used for the capacity and delay estimation model. Using developed countries design and operation manuals in developing countries without modification would give misleading results. 1. INTRODUCTION Intersections are shared areas of joining or crossing roadways. Intersections permit pedestrian and vehicular traffic crossing and direction change. Major elements of Intersections design and performance include human factors, traffic characteristics, physical elements and economic factors. Traffic control system is utilized to resolve the right of way conflicts between merging, diverging and crossing traffic streams. This is often achieved by time separation of the different traffic stream movements through traffic control sign and signaling systems. These systems include no control, guide signing, warning signing, yield control, stop control, red and yellow blinking signals, and signalization. Stop signs and blinking red signals are often installed at intersection minor-street approaches. This is when the warrants for intersection traffic control devices only mandate stop sign and/or blinking red signals. The warrants are related to vehicular traffic volumes and platooning, pedestrian volumes accident rates, signal spacing, adjacent land use and environment characteristics. Performance of a non signalized intersection is directly related to driver and pedestrian behaviors. These include attributes on the tasks of driving, walking, and information handling. Vehicles approaching a stop sign or blinking red signal should come to complete stop and then enter in to the intersection with due considerations of right of way and hazards (Vaziri 2000). Several developing countries have found that using developed countries design and operation manuals without modification could give misleading results. This is mostly due to the existence of developing countries different traffic behavior and composition. Knowledge of driver behavior is essential in intersection design and operation. 3. DATA COLLECTION In order to compare and calibrate the algorithm which is introduced by HCM, some non signalized intersections in Tehran were selected to study. These intersections are located in different parts of the city. Using a video camera with a timer, the traffic behavior was taped during working days. Video taping is a simple and inexpensive way of traffic behavior data collection. It is very invaluable for data review and verification. Number and type of vehicle in each movement and movement travel time were two main groups of information which were extracted from the display on television screen. In order to analyze driver behavior with questionnaire, several non signalized intersections were studied and about 1500 drivers were selected to fill in the questionnaires. Among the selected samples, about 1100 drivers filled in the questionnaires correctly. In selecting the samples, some points were taken into consideration. For example, the questionnaires were filled in different times of the day. Moreover, various kinds of vehicles and drivers were chosen to fill in the questionnaires. Figure 1. Number and type of studied movements a 18 to 22 M 22 to 36 □ 36 to 60 □ >60 Figure 2. Age of drivers in studied samples 4.2 Results of the questionnaires analysis After analyzing selected intersections and processing the information extracted form the questionnaires these results can be presented: 1. Sight distance at non signalized intersection is an important factor for drivers to recognize critical gap. 2. At intersections in which the major street has several lanes drivers in minor streets accept the gap in several stages. 3. In saturated intersections, drivers in minor streets produce the acceptable gap in more than one stage. 4. Among the studied samples, 68 percent of drivers increased their Speed when they wanted to produce acceptable gap. In other words, they made the drivers in major Street to stop or to decrease their speed. 5. Accepted gap for most of the drivers were 2 to 3 seconds. 6. Accepted gap for left- turn movements were greater than those of through or right- turn movements. 7. Drivers which were 22 to 35 years old accepted shorter gap than the older ones. 8. Accepted gap for women were 2 or 3 seconds more than men. 9. Accepted gap for drivers having new and expensive vehicles were greater than those having old vehicles. 5. MODIFICATION THE VALVE OF GAP AND FOLLOW- UP TIME In this part, the value of gap and follow- up time were extracted from video displays. As it was explained in previous sections, gap is the time for the front bumper of the second of two successive vehicles to reach the starting point of the front bumper of the first. Sometimes the vehicle accepts the gap and some time rejects the gap. The process by which a minor-street vehicle accepts an available gap to maneuver is called acceptance gap. The critical gap is defined as the minimum time interval in the major-street traffic stream that allows intersection entry for one minor-street vehicle. Thus, the driverʹs critical gap is the minimum gap that would be acceptable. A particular driver would reject any gaps less than the critical gap and would accept gap greater than or equal to the critical gap. Estimates of critical gap can be made on the basis of observations of the largest rejected and smallest accepted gap for a given intersection. The time between the departure of one vehicle from the minor street and the departure of the next vehicle using the same major-street gap, under a condition of continuous queuing on the minor street, is called the follow up time. In order to calculate the critical gap, the amount of gaps which were accepted and rejected by vehicles was classified. The samples which were not influenced directly by the major-street vehicles were omitted. For example, left turn or right turn in major street does not have direct effect on the right turn in minor street. After extracting and classifying the accepted and rejected gaps, RAFF model was used to determine the value of critical gap form field data (Harwood 1999). Calculating the critical gap for through movements is shown in Figure 3. 656 samples were considered in this study. 160 samples for right, 370 samples for through movement, and 126 samples for left turn were studied. The point where two curves cross illustrates the critical gap. As shown in figure 3 and 4 the critical gap is 2.25 second for through movement and 1.44 second for left turn. Table 2 illustrates the amount of critical gap and follow-up time for non signalized intersections in Tehran. These parameters are calculated in the same way. Table 2. Computed critical gap and follow- up time for Tehran non signalized intersections Vehicle Maneuver Critical gap (sec) Follow- up time (sec) RT 1.47 1.25 TH 1.44 1.1 LT 2.25 1.6 6. Validity of computed parameters As it was described before the value of critical gap and follow- up time were computed for Tehran non signalized intersections. By replacing the modified parameters in HCM equations given for computation delay at non signalized intersections and delay at studied intersections were computed. Table 3 illustrates the delay at some studied intersections NO EB WB SB NB intersections Field delay (sec) 17.7 27.3 21 - 31.8 1 HCM delay (sec) 0 3.9 65003 - 27276 Modified HCM delay (sec) 0 1 112.3 - 32.7 Field delay (sec) 4.4 11.8 8 - 6.61 2 HCM delay (sec) .5 1906 4978 - 1247 Modified HCM delay (sec) .5 44.5 56.4 - 18.54 Field delay (sec) 32.68 - 21.4 10.1 20.6 3 HCM delay (sec) 32079 - 7.8 2.6 7042 Modified HCM delay (sec) 169.9 - 1 2.5 34.8 As shown in Table 3, the field observed delay, HCM delay, and Modified HCM delay for each intersections have been compared. Delays computed by HCM equations specially for minor-street approaches are not rational, but those computed by Modified HCM equations are closer to real delays. Figure 4 illustrates comparison of real delays at selected intersections and Modified HCM delays. Correlation coefficient in this regression is 0.88. MODIFIED HCM DELAY(sec) Figure 4. Comparison of real field delay and Modified HCM delay 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 0 7. Conclusions The traffic behavior at non signalized urban intersections for the city of Tehran was studies. Information about the traffic behavior was collected by video camera at non signalized intersections. Other information was collected by questionnaires. Questionnaires were filled in by 1100 drivers at selected non signalized intersections. Analysis of the forms showed that there by 1100 drivers at selected non signalized intersections. Analysis of the forms showed that there are several differences between the driver behaviors in the capital of a typical developing country and driver behaviors in developed countries. Some parameters like gap, follow- up time, delay, and traffic volume were extracted form video displays. Large differences between real field delay at non signalized intersection and those computed by HCM equations showed that HCM equations cannot be used in developing countries without any modifications. It is necessary to modify the HCM equations for developing countries and then put them in use. critical gap and follow-up time were computed by extracted information. By replacing the modified parameters in HCM equations new equations were resulted. Delays derived from modified HCM equations were closer to the real field delays. Using developed countries design and operation manuals in developing countries without modification would give misleading results. Because performance of an non signalized intersection is directly related to driver behaviors, each developing country should modify the equations with its own characteristics.