BLOSSOM AT PICKENS SIGNALIZED INTERSECTION IMPROVEMENT STUDY

Transcription

1 BLOSSOM AT PICKENS SIGNALIZED INTERSECTION IMPROVEMENT STUDY Class Project Report for ECIV 542 Traffic Engineering Submitted by Omor Sharif Muchun Song Narges Kaveshgar Quyen Pham Chih-Yao Lin Submission Date: November 23, 2010 Fall, 2010 Department of Civil and Environmental Engineering University of South Carolina

2 1. Introduction In many cities of the world the intersections constructed need to be modified with regard to the new situations and changes that gradually would take place through time, like changes in the population, number of car owners land use, etc. Remaining in their original configurations since they have been once constructed would cause numerous problems for the road users. The traffic control devices also have to be modified since over the years; there will be changes in travel mode and trip patterns. Current study considers the intersection located at Pickens St. and Blossom St., Columbia, SC. First relevant traffic data is collected at the selected intersection in AM and PM peak hour to investigate the present conditions at the intersection. Subsequently, collected data for consideration of potential efficiency improvement options at the intersection is analyzed using Synchro 6 a software package. Drawings are used in order to illustrate the suggested changes in layout. 2. Literature Review By looking at similar studies that has taken place in different cities, one could easily realize the importance of the intersection studies and improvement and its major impact on traffic situation for the users. Some of these studies could be listed as follows: Intersections Improvements Study (2009) which is done for City of Piqua, Ohio [1]. It includes 27 intersections which 22signalized intersections, 3 four-way stop controlled, and 2 two-way stop controlled. As mentioned in the report the purpose of the study is to fully assess the traffic control devices and physical characteristics of the improvements found at certain locations throughout the City. The main goals of the study are mentioned as: 1-Conduct limited research of historical traffic and land development records 2- Positively identify the warrant status of the existing traffic control devices being utilized at each location and identify the traffic control device and incidental improvements that will enhance the functionality, level of service, and level of safety of each intersection. 3- Fully assess the existing design characteristics of the physical improvements found at each location, and identify any existing deficiencies or opportunities regarding the geometric configuration and functionality of the intersection 4- Fully assess the physical characteristics of the built environment surrounding each location to identify any existing deficiencies or opportunities regarding coordination between the use of buildings, landscaping, public spaces, sidewalks, streets, bike lanes/trails, on-street and offstreet parking, and the like. 5- Provide alternative recommendation for modifications specific to each intersection in consideration of the findings and determinations of items 1 through 4 above. 6- Estimate the cost to implement the alternative improvements for each intersection, including the demolition and or removal of existing improvements, and the construction and or installation of any new improvements.

3 7- Provide all documentation, completed forms, and analysis necessary, and a strategy for the implementation of the traffic control device removal, modification, or enhancement recommendation selected for each intersection by the City. The methodology of the study includes three components: data collection, input/awareness, and traffic analyses The other interesting report would be Oldham County Intersection Improvement Study Report (2006) conducted on Oldham County, Kentucky [2]. The main goals of the study are increasing the capacity and also managing the congestion. As mentioned in the report the study team considered two alternatives for each intersection: upgraded signalized intersection and construction of a modern roundabout. Moreover, Intersection Improvement Study Hendricks County Road 100 South & Dan Jones Road Avon, Indiana [3] could be considered as a good source for interested researches. The software used for the intersection analysis is Synchro 6 which is a complete software package for modeling and optimizing traffic signal timings. To determine the intersection capacity, Synchro uses the Intersection Capacity Utilization (ICU) 2003 approach. This method compares the current volume to the intersections ultimate capacity. Synchro also implements the methods of the 2000 Highway Capacity Manual, Chapters 15, 16, and 17; Urban Streets, Signalized Intersections, and Unsignalized Intersections. Synchro provides an easy-to-use solution for single intersection capacity analysis and timing optimization [Synchro Help]. In order to analyze the intersection the criteria for LOS from HSC (Highway Capacity Manual) is considered. Table 1: Level of Service Criteria - Signalized Intersections LOS Seconds Delay/Vehicle Description A 10 Most vehicles do not stop at all. B >10 and 20 More vehicles stop than for LOS A. C >20 and 35 The number of vehicles stopping is significant, although many pass through without stopping. D >35 and 55 Many vehicles stop. Individual cycle failures are noticeable E >55 and 80 Considered being the limit of acceptable delay. Individual F >80 Unacceptable delay. Source: Transportation Research Board, Highway Capacity Manual Data Collection Before we evaluate the current performance of intersection, we collected traffic volume data by JAMAR Traffic Counter and signal timing data by stop watch. JAMAR Traffic Counter is counting equipment that is manufactured by JAMAR Technology Inc. On October 21, 2010, we stood at the southeast corner of intersection of Pickens St and Blossom St to record traffic volume during morning peak hour (7:00am-9:00am) and evening peak hour (4:00pm-6:00pm). Besides

4 traffic volume of the intersection, we also collected the signal timings of intersection, such as total cycle, green phase, yellow phase and all red of signal timing. 4. Characteristics of the Intersection The intersection of Blossom St and Pickens St studied under this class project is located very close to downtown Columbia and within Columbia campus area of University of South Carolina. Some major characteristics such as geometric, traffic and signal attributes of the intersection are presented below. a) Geometric Features The four legged symmetric intersection is the crossing of Blossom Street running east-west and Pickens street running north-south. The major approach Blossom St has two lanes with an additional storage bay (200 ft long) for left turning vehicles in both directions. The lanes are 12 ft wide without any exclusive turning restrictions. The minor approach Pickens St has two 10 ft wide lanes in both northbound and southbound directions and the left lane is restricted to left turning movements. Traffic with through movement on the Pickens St is provided with a single lane after they cross the intersection. The southbound Pickens St approach has a steep downward 4% grade. Medians and shoulders are present on the major street only. One notable driveway in the vicinity of the intersection include a multistoried apartment facility located about three hundred feet south of the intersection on Pickens ST. Sidewalks, crosswalks and push buttons are present on all four sides of the intersection for pedestrians. Fig 1 shows the current condition of intersection at Blossom St and Pickens St. b) Traffic Features- The posted speed limit are 35 mph and 30 mph on major Blossom St and minor Pickens St respectively. The maximum hourly volume for the entire intersection was found 2215 veh/hr with a PHF of in the AM peak hour and 3574 veh/hr with a PHF of in the PM peak hour. Since the intersection is located within Columbia campus of University of South Carolina, an appreciable number of pedestrians also add to the traffic. During the study period, the pedestrian volume reached a PM peak of 76 pedestrians/hour in northbound direction. Only few heavy vehicles are present in traffic thus we assume a default 2% HV suggested by Synchro. c) Signal Characteristics- A two phase signal plan is in place at the intersection. The type of signal operation adopted is semi-actuated with detectors placed only on the minor Pickens St. Thus green time on Pickens St is based on the traffic demand on that approach. No protected turning movements are provided by the signal operation. Left turns are treated as permitted during green ball for all approaches. Right turns are permitted on red. The cycle length is 134 seconds. The yellow interval and all red for both phases are 3 seconds and 2 seconds respectively.

5 Fig 1 Current Condition of Intersection at Blossom St and Pickens St

6 5. Analysis with SYNCRO As we know the traffic volumes, number of lanes, number of approaches, storages and width of lanes. We input all the parameters into Synchro to analyze the current performance of intersection. The performance report of intersection is shown below:

7 From the two analysis reports above, we can figure out the ICU Level of Service in morning peak hour is B and in evening peak hour is E. Thus we will propose some improvements to make ICU Level of Service better in evening peak hour. 6. Proposed Improvements In this section we propose and investigate some considerations to improve the performance of the intersection. Widely accepted performance indicators for a signalized intersection are Level of Service, vehicle/capacity ratio and approach delay for the traffic etc. The intersection performs poorly in these respects at least in the PM peak hour as indicated in section 5. To this

8 end we have considered some modifications to the existing intersection characteristics that include geometric and operational changes. They are briefly discussed below- a) Increasing lane width The first option we have considered is to increase the lane width on minor Pickens St. The minor approach does not have any shoulders but close off directly to the curb. The existing lane width is 10 ft which is noticeably narrow. Narrow width causes reduced efficiency and comfort as they force the drivers to operate their vehicles closer in lateral direction than they desire and they tend to avoid driving side by side. Narrow lanes are only suitable to light traffic conditions, however our traffic count shows that high traffic demand exist on minor street (1137 veh/hr total for northbound and southbound approach). Increased width of travel lanes increases capacity, approach speed, safety. Thus, we propose a revised lane width of 12 ft to be considered at Pickens St for improving efficiency of traffic operation on that approach. AASHTO (2004) also recommends 12 ft as optimal width of lanes. b) Right turn channelization Another improvement option we have investigated is to introduce channelized right turns on minor street with a yield control. Traffic count reveals significant number of right turns from minor street. For instance, during PM peak hour right turns consist of 40 percent of total through and right turning traffic volume that shares a single lane in the Pickens St. Sharing of a single lane by turning and through traffic causes the saturation flow rate to be reduced as a result. In addition, channelized right turns have the advantage of minimizing the probability of a right turning vehicle being caught behind a through vehicle during red ball. Also, it might be possible to eliminate the right turning traffic from signalization design since in most cases they are yield controlled and allowed to flow continuously. Taking this fact into account we have revised the Synchro analysis by adding channelized RT lanes on Pickens St approach. We have found the LOS to be improved to E from existing F. The approach delay is reduced to 65 seconds from 205 seconds and v/c ratio of 1.06 from 2.51 in the northbound direction. However, to realize this benefit care must be taken during design of channelization such that queue of through vehicles in the right lane do not block access to channelized lane. Also, the ICU level of service for the entire intersection upgrades to D from existing ICU LOS of E. c) Adding lanes Another physical change to the intersection we have considered is providing an additional travel lane to the minor street to increase capacity in that direction. This is because one shared lane to serve high volume of through and RT traffic is inadequate as suggested by our Synchro analysis results. Based on existing characteristics of the intersection, the analysis indicates that a level of service F exists at both approach of minor street at PM peak hour. The delay was found 204 seconds and 92 seconds for northbound and southbound approach respectively. The v/c ratio of 2.51 in northbound direction is significantly higher and inhibits an efficient operational condition. These results are indicative of considerable performance deficiency. Thus, we recommend an additional lane on minor street to reduce approach delay and v/c ratio and consequently to improve LOS. This, of course, involves an investigation of adequate right of way and feasibility study prior to implementation. We have revised the Synchro analysis to appraise the performance gain by adding a lane and have found the LOS to be improved to D

9 with an approach delay reduced to 53 seconds and v/c ratio of 1.06 in the northbound direction. Also, the ICU level of service for the entire intersection upgrades to D from existing ICU LOS of E. d) Signal Timing Optimization Intersection improvement can be accomplished by physical changes to the intersection and/or changes in signal timing characteristics. Section 6a-6c discussed considerations for physical changes to enhance operational performance. Nonetheless, changes in timing plan (such as revised cycle length, phase plans, interval lengths etc) can also contribute to operational efficiency and is particularly encouraging since they do not require costly physical alterations. However, a complete investigation of signal timing involve many considerations and a separate topic on its own and therefore beyond the scope of our work. However, we have tried a simple intersection split optimization in Synchro. Based on the existing characteristics, Synchro suggest a total split of 62 seconds and 64 seconds phase lengths in PM peak hour in major and minor street respectively (instead of observed 80 seconds and 54 seconds respectively). It improves the minor street operation LOS F to LOS D, however major street westbound operation LOS drops from LOS E to LOS F. Another option would be to optimize cycle length. Nonetheless, results indicate that performance cannot be enhanced significantly by changing timing plan only, physical addition of capacity is necessary. 7. Conclusion This project report intends to provide an overview of several considerations that may be undertaken to improve the operational performance of the intersection of Blossom St and Pickens St. The case study began with collection of geometric, traffic and signal characteristics data at the intersection. The intersection was selected since we were suspecting poor performance of the intersection (especially in minor approach) by observation and personal driving experience through the intersection. Subsequently a HCM signalized intersection analysis was carried out in Synchro software based on the collected data that confirmed the inferior performance by the intersection. Analysis shows that LOS and approach delay are below acceptable range especially in the PM peak hour and thus considerations for improvement options were necessary. We have attempted to identify the sources of bottlenecks in the intersection that include narrow lane width, limited number of lanes (high v/c ratio) and large right turning traffic from shared through lane etc. We proposed improvement alternatives in these areas and have confirmed our findings via analysis in Synchro. However, it should be noted that the scope of our work is limited to class project thus not intended to be a comprehensive analysis. For example, though we primarily emphasize promoting efficiency in performance, safety is also a major objective that should be considered as a part of intersection improvement study.

10 8. References 1. Intersections Improvements Study, Prepared for the City of Piqua Ohio, January 2009, Kleingers & Associates, Inc. 2. Oldham county intersection improvement study report oldham county, Kentucky, December 2006, DLZ Kentucky, Inc. 3. Intersection Improvement Study Hendricks County Road 100 South & Dan Jones Road Avon, Indiana, November 2003, DLZ Indiana, LLC 4. Manual of Uniform Traffic Control Devices, Federal Highway Administration, U.S. Department of transportation, Washington DC, December Highway Capacity Manual, 4th Edition, Transportation Research Board, National Research Council, Washington DC, A policy on Geometric Design of Highways and Streets, 5 th Edition, American Association of State Highway and Transportation Officials (AASHTO), Washington DC, Traffic Engineering, 4 th Edition, R. P. Roess, E. S. Prassas and W. R. McShane, Prentice Hall New Jersey, SYNCHRO 6, Synchro plus SimTraffic User Guide, Trafficware Ltd.,

11 Appendix