National Academies Press: OpenBook

Adaptive Traffic Control Systems: Domestic and Foreign State of Practice (2010)

Chapter: Chapter Two - Overview of Deployments

« Previous: Chapter One - Introduction
Page 10
Suggested Citation:"Chapter Two - Overview of Deployments ." National Academies of Sciences, Engineering, and Medicine. 2010. Adaptive Traffic Control Systems: Domestic and Foreign State of Practice. Washington, DC: The National Academies Press. doi: 10.17226/14364.
×
Page 10
Page 11
Suggested Citation:"Chapter Two - Overview of Deployments ." National Academies of Sciences, Engineering, and Medicine. 2010. Adaptive Traffic Control Systems: Domestic and Foreign State of Practice. Washington, DC: The National Academies Press. doi: 10.17226/14364.
×
Page 11
Page 12
Suggested Citation:"Chapter Two - Overview of Deployments ." National Academies of Sciences, Engineering, and Medicine. 2010. Adaptive Traffic Control Systems: Domestic and Foreign State of Practice. Washington, DC: The National Academies Press. doi: 10.17226/14364.
×
Page 12
Page 13
Suggested Citation:"Chapter Two - Overview of Deployments ." National Academies of Sciences, Engineering, and Medicine. 2010. Adaptive Traffic Control Systems: Domestic and Foreign State of Practice. Washington, DC: The National Academies Press. doi: 10.17226/14364.
×
Page 13
Page 14
Suggested Citation:"Chapter Two - Overview of Deployments ." National Academies of Sciences, Engineering, and Medicine. 2010. Adaptive Traffic Control Systems: Domestic and Foreign State of Practice. Washington, DC: The National Academies Press. doi: 10.17226/14364.
×
Page 14
Page 15
Suggested Citation:"Chapter Two - Overview of Deployments ." National Academies of Sciences, Engineering, and Medicine. 2010. Adaptive Traffic Control Systems: Domestic and Foreign State of Practice. Washington, DC: The National Academies Press. doi: 10.17226/14364.
×
Page 15
Page 16
Suggested Citation:"Chapter Two - Overview of Deployments ." National Academies of Sciences, Engineering, and Medicine. 2010. Adaptive Traffic Control Systems: Domestic and Foreign State of Practice. Washington, DC: The National Academies Press. doi: 10.17226/14364.
×
Page 16

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

10 INTRODUCTION From the 45 agencies that responded to the survey (34 of 42 from North America and 11 agencies from other countries), the major contributors were municipal, county, and state traf- fic operations agencies with proportions of 42%, 20%, and 13%, respectively. All other organizations (regional orga- nizations, federal government, consultants, and others) con- tributed with 25%. These findings indicated that the ATCSs are mostly operated by local agencies. Geographical locations of the ATCS deployments, which are found in Table 1, show that most of the U.S. ATCS users are located in California and Florida. This chapter identifies factors that dominate deci- sions to install an ATCS and those factors that describe the environment in which these systems operate. OPERATIONAL ENVIRONMENT Table 2 shows the number of signals operated by the inter- viewed ATCS agencies. It can be observed that some agencies operate a wide range of traffic signals. Several of the agencies have a very low percentage of signals under ATCS, whereas others run most of their signal operations through an ATCS. Statistics show that, on average, 25% of all signals under the jurisdiction of the interviewed agencies are operated under ATCSs. However, this number is heavily weighted by a few agencies that almost exclusively operate ATCSs. If one con- siders only systems where an ATCS is not the predominant type of traffic control (the number of signals under an ATCS is lower than the number of non-ATCS signals) the ATCS’s share drops to 13%. The survey results report that most of the interviewed agencies (80%) deployed ATCSs in the network with speed limits between 30 and 45 mph. Therefore, from that perspec- tive, in most cases, ATCSs are installed in the environment in which they can contribute to reducing traffic congestion and improving overall operations. Predominant speed limits on arterial streets may have an impact on the achievable benefits of ATCS implementation. If the speed limits are too low (e.g., lower than 30 mph), it may indicate that a lot of intermodal traffic exists and urban rights-of-way (ROWs) are shared between vehicles, pedes- trians, bicyclists, etc. On the other hand, if the speed limit is too high (e.g., greater than 45 mph), it may be an indication that the network has a high-priority arterial(s) with inter- sections of streets with different priorities. In either circum- stance, lower or higher speed limits, ATCSs may need addi- tional fine-tuning to achieve acceptable operational results. Another factor for the success of an ATCS is type of the network layout where an ATCS is deployed. Some ATCSs are known for their ability to provide balanced traffic control on grid networks. Others are known for their ability to adjust signal timings on corridor-type networks. In European cities, where road networks have more irregular shapes than in North America, controlling traffic on gyratory networks is also an important objective. Survey results show that approx- imately 42% of all agencies have deployed ATCSs solely on arterial networks, 10% deployed ATCSs on grid networks, and 33% deployed ATCSs on the combination of the two net- work types. IMPLEMENTATION OF ADAPTIVE TRAFFIC CONTROL SYSTEMS The type and quality of the pre-ATCS traffic signal systems is probably the most influential factor for determining the mag- nitude of benefits that can be achieved with an ATCS imple- mentation. There is an abundance of studies that show benefits when an ATCS replaces an aged fixed-time, or actuated- isolated, traffic signal system. However, the benefits of replac- ing a properly fine-tuned actuated-coordinated control may not always be so evident. From that perspective, it is impor- tant to investigate what types of traffic control were run by responding agencies before they installed ATCSs. Statistics from the questionnaire reported that most of the agencies did not run a single type of control on their networks where ATCSs are now installed. Instead, most of them ran combinations of fixed-time and/or actuated controls where some intersections were coordinated, whereas the others were isolated. Table 3 shows the percentages of agencies that used relevant types of traffic control before they deployed an ATCS. These percent- ages show that actuated-coordinated control was the most widely used system in pre-ATCS networks. There are many reasons why agencies that operate traffic signals may decide to deploy an ATCS. Some agencies are looking for a traffic control system that will be able to handle high day-to-day variations in traffic. For other agencies the primary reason for installing an ATCS may be the reduction in costs to retime signal timings every 3 to 5 years, which may be necessary owing to the steady increase in traffic demand and changes in traveler’s patterns. Other major reasons for deployment of an ATCS are shown in Figure 1, which shows CHAPTER TWO OVERVIEW OF DEPLOYMENTS

11 how ATCS users ranked nine different reasons for deploying such a system. Although there is no reason that is clearly predominant, one can observe that handling day-to-day and within-the-day traffic variations was ranked as the most important reason for deploying an ATCS. Surprisingly, if only a single factor with the highest rank for each ATCS deployment is considered then results show that such a sys- tem was most frequently deployed because: • The agency served as a testing facility/early deployer of an innovative signal control method—seven ATCS deployments. • It was recognized that an ATCS would help to resolve conflicts between vehicular traffic and other modes (pedestrian, transit, etc.)—five ATCS deployments. • There was funding available for capital Intelligent Trans- portation System (ITS) projects and ATCS deploy- Agency Total No. of Signals No. of Signals under ATCS City of Menlo Park, CA 32 13 Reedy Creek Improvement District, FL 35 7 City of Blackpool Council, UK 77 50 City of Sunnyvale, CA 128 23 City of Gresham, OR 130 City of Longview, TX 132 16 City of Red Deer, Canada 133 89 City of Ann Arbor, MI 150 34 Town of Cary, NC 150 16 Collier County, FL 160 16 City of Chesapeake, VA 166 3 Unidad Operativa de Control de Tránsito, Concepcion, Chile 197 15 City of Santa Rosa, CA 200 9 City of Southampton, UK 200 200 Pasco County, FL 220 35 Hampshire County Council, UK 225 69 Halifax Regional Municipality, Canada 260 80 City of Chula Vista, CA 265 11 City of Anaheim, CA 300 0 City of Little Rock, AR 350 4 Pinellas County, FL 370 City of Tucson, AZ 375 15 Washington State DOT, WA 520 10 Cobb County, GA 526 74 Orange County, FL 572 70 Minnesota Department of Transportation, MN 675 0 Dublin City Council, Ireland 783 614 City of Minneapolis, MN 800 New Zealand Transport Agency, Auckland, NZ 800 750 Delaware Department of Transportation, DE 850 30 Utah Department of Transportation, UT 1,100 16 California Department of Transportation— District 7, CA 1,350 180 Road Commission for Oakland County, MI 1,500 650 City of Toronto, Canada 2,100 340 Grea ter Manchester Urban Traffic Control Unit, UK 2,200 2,200 11 33 56 Victoria Roads, Victoria, Australia 3,000 2,500 RTA, New South Wales, Sydney, Australia 3,800 3,500 Los Angeles Department of Transportation, CA 4,300 3,000 TABLE 2 NUMBER OF SIGNALS OPERATED BY PARTICIPATING AGENCIES Type of Traffic Control Before ATCS Deployment Percent of Agencies Utilizing Traffic Control Actuated coordinated 76 Fixed-time coordinated 31 Actuated isolated 22 Fixed -time isolated 7 Note: Total percentage exceeds 100 because some agencies deploy multiple types of traffic control at various intersections under their jurisdiction. TABLE 3 TRAFFIC CONTROL UTILIZED BEFORE ATCS DEPLOYMENT

ment was funded under such a program—three ATCS deployments. Some of these reasons (e.g., availability of funding or an interest in being an early deployer of a new technology) may indicate that sometimes decisions to deploy an ATCS are made at higher political levels at deploying agencies. If these ATCS deployments are made in an ad hoc manner or they are planned and executed without support from people who operate and maintain traffic control systems, the decision may have negative consequences. More research is needed to inves- tigate how agencies make decisions to deploy ATCSs and whether decisions are made in coordination with opera- tional staff. Depending on an agency’s preferences and defined pro- cedures for procurement of ITS technologies the process of selecting an ATCS may be more or less complex. Some agen- cies conduct internal short reviews of the available systems 12 before they make final decision of which system to install. Others go through a lengthy procurement process in which at times the lowest-bid option wins. Third, agencies hire outside consultants to do the review process and suggest the best ATCS for the operational conditions of an agency’s deployment. The survey questionnaire asked agencies about their consid- eration of other ATCSs before the final selection was made. Most agencies responded that other systems were considered, although the current system was selected because it appeared that it was the best fit for the agency’s needs. Of the 45 respond- ing agencies, approximately 25% considered only the system that was later deployed. Approximately 12% of the agencies went through a complete ranking process, where multiple ATCSs were reviewed in the ATCS procurement process. Table 4 shows the major reasons that motivated agencies to select a particular ATCS for deployment. One particular agency (LA DOT) decided to further enhance its Urban Traf- fic Control System, which resulted in the development of its own ATCS platform. FIGURE 1 Major reasons for implementing an ATCS. Reducing costs of retiming signals; 46; 12% Handling oversaturated traffic conditions; 48; 12% Handling traffic special events; 47; 12% Handling high day-to-day and within-a-day traffic variability; 69; 17% Handling conflicts between vehicular traffic and other modes; 37; 10% Serving as an early deployer of innovative technology; 33; 9% Availability of funding for capital ITS projects; 36; 9% Expecting significant operational savings & high b/c ratio; 60; 16% Other; 11; 3% Reasons to Select Current ATCS for Deployment Percent of Agencies Proven record of previous ATCS deployments 12 Only considered ATCS s known to work best for agencyís network 12 Compatibility with existing communications and hardware 12 Friendliness of ATCS software 3 Note: Total percentage is lower than 100 because only 39% of the interviewed agencies responded to this question. TABLE 4 MAIN REASONS FOR SELECTING AN ATCS FOR DEPLOYMENT

13 Adaptive Traffic Control System Deployments Figure 2 shows the percentages of the ATCSs deployed by the responding agencies; it is noticeable that SCOOT and SCATS are still the most dominant. However, these results are cor- related to the maturity of the systems and their presence on the market. Although SCOOT and SCATS were developed almost 30 years ago, and they have been present in United States for approximately 15 years, several other systems are much younger. It can also be noted that some of the U.S.- developed systems have been deployed with support from the FHWA or similar U.S. federal agencies, whereas most of SCOOT and SCATS deployments were pure commercial proj- ects. This dominance of SCOOT and SCATS is further con- firmed among larger ATCS deployments; those having 50 or more intersections under an ATCS. Almost all larger ATCS deployments (except LA DOT) use either SCOOT or SCATS. The major reason for the popularity of SCOOT and SCATS may be found in the maturity of these systems and because they enjoy strong support from their developers and consul- tants. One of the limitations of the results presented in Fig- ure 2 is that they do not include most of the ATCS deploy- ments in continental Europe. Agencies from that part of the world did not show a great interest in participating in the survey. The installation of an ATCS can be a lengthy and difficult process. If the network where an ATCS is being installed is in a high-growth area, interaction between ATCS installation and other ongoing projects may significantly affect installation time. The availability of local consulting, condition of existing infrastructure (detection, hardware, and communication), and availability of funding may all influence the duration of the installation process. ATCS agencies reported that, on average, installation of such a system takes approximately 18 months and is measured from the time when funding is made avail- able until the ATCS is fully operational. Table 5 shows the distribution of ATCS deployment times for various installa- tion intervals, which range from fewer than 3 months to more than 2 years. Other; 4; 9% SCOOT; 15; 33% SCATS; 15; 34% RHODES; 4; 9% OPAC; 3; 7% LA ATCS; 2; 4% ACS-Lite; 2; 4% FIGURE 2 Market shares of various ATCSs. Installation Intervals Percent of Agencies Less than 3 months 7 Between 3 and 6 months 7 Between 6 and 12 months 23 Between 1 and 2 years 33 More than 2 years 30 TABLE 5 TIMEFRAMES FOR ATCS DEPLOYMENTS

Of the 45 agencies that were interviewed, 38 have currently operational ATCSs. One agency only tested an ATCS and removed it after the probationary period owing to its incom- patibility with the existing infrastructure (a communication problem between the ATCS and local controllers). Another agency considered the deployment of an ATCS, but found that benefits were too uncertain, and decided to operate an actuated-coordinated system. Finally, five agencies shut down their ATCS operations for various reasons. It appears that these shut-downs were not consequences of single problems but more a result of several factors that occurred simultane- ously. The five agencies that shut down their ATCSs provided the following reasons to justify such actions: • Agency 1—improper detection layout and other opera- tional problems. • Agency 2—multiple simultaneous events: budget reduc- tions, staff reassignments, and construction projects resulting in significant removal of system detection. • Agency 3—operational problems; agency did not shut down the entire system, but it converted most of the ATCS signals to actuated-coordinated operations. • Agency 4—system incompatibility with ramp-metering where integration of arterial and ramp operations was required. • Agency 5—no operational benefits achieved; problems with hardware and software. Once an ATCS is installed, the system can provide not only traffic-adaptive operations but also other control modes (actuated-coordinated TOD plans, isolated control, etc.). The variety of traffic control systems offered under the ATCS umbrella provides agencies with the opportunity to run ATCSs 24 hours per day and 7 days per week. If agencies do not let the ATCS control traffic on a 24/7 basis this may indicate that they do not have full confidence in ATCS operations. Also, if an ATCS is working properly and an agency experiences its operational benefits it would be logical that the system be expanded (spatially) to other neighboring traffic signals or entire signal systems. The results from the survey indicate that the high costs of ATCS deployments are the most com- mon obstacle to expanding current ATCSs temporally and spa- tially (in 50% of the cases). The second factor, by its impor- tance, is the lack of traffic signal operations staff—a problem that can also be attributed to inadequate funding (12%). Finally, 13% of the agencies reported that the operational inefficiency of their ATCSs is the major reason why they have not expanded their systems. The following are examples of the agencies’ responses: • Insufficient staff and funding to operate and maintain; • Poor communications between vendor and client; • Not cost-effective if volume fluctuations are insignificant or where cycle lengths and splits are quite constrained to meet operational objectives; • Because it is very expensive for the licensing fees and very sophisticated to set up and fine tune. In addition, it 14 requires much vehicle detection that is well-maintained and working properly; • Difficult to program and data intensive; • High cost of supplying communications or low priority sites; and • Only use it at times of high traffic flows as standard vehicle actuation is more reactive at quieter times when linking becomes less important. Despite these difficulties, a significant number of the inter- viewed agencies have expanded their ATCSs since the initial deployments. Actually, only 30% of the agencies have not expanded their ATCSs at all. Fourteen percent of the agen- cies had one expansion of their systems, and another 14% had two expansions. Finally, 42% of the agencies expanded their ATCSs three or more times. Fifty percent of all these expansions were small expansions where a few neighboring intersections were added to the initial ATCSs, whereas the other 50% were major expansions onto neighboring corridors of traffic signal systems. Some agencies developed long-term expansion plans, where they steadily increase their ATCSs by a certain number of intersections per year. Traffic Signal Operations Staff The size and expertise of the traffic signal operations staff may significantly affect the success of an ATCS deployment, as well as deployment of any other traffic signal system. The size of the traffic signal operation team largely varies with the size of the agency and available financial resources. The survey results revealed that the traffic signal operations staff can be a single person or a team of more than 50 people (see Figure 3). Figure 3a shows average, median, and mode values of the overall sample of interviewed agencies. Differences between statistics show that large agencies significantly increase the average number of staff employed, whereas median and mode more realistically show frequent, inadequate levels of staff- ing at small- and medium-size agencies. Figure 3b shows a relationship between the number of signals under an agency’s jurisdiction and the number of signal timing staff. One could note that a linear relationship would not fit the data properly because it would set an intercept unacceptably high (∼10), which would be a very unrealistic estimate. Overall, more than 25% of the agencies have five or fewer people in their traffic signal operations staff. These findings show that a sig- nificant portion of the agencies that operate an ATCS are understaffed and that a lack of qualified personal may be one of the major problems for potential performance issues of their ATCS deployments. Most of the ATCS users reported that they are familiar with the operations of their systems. Thirty-one percent of the ATCS users know their systems very well, whereas 38% have a good working knowledge. Twenty-four percent of respondents understand their systems but do not consider themselves to

15 0 1 2 3 4 5 6 Engineers Timing technicians Field technicians Maintenance technicians Others Staff category N um be r o f s ta ff Average Median Mode (a) y = 0.1973x0.6708 R2 = 0.6527 0 10 20 30 40 50 60 0 500 1000 25001500 30002000 4000 50003500 4500 Number of signals N um be r o f s ta ff (b) FIGURE 3 (a) Statistics of timings staff; (b) Number of signals versus number of staff.

be specialists. Finally, 7% of the respondents have a limited understanding of their systems’ operations. In general, agencies are satisfied with their ATCSs. Eigh- teen percent of the respondents claimed that they are very satisfied, whereas 61% are only somewhat satisfied. Figure 4 also shows that approximately 11% of ATCS users do not see either advantages or disadvantages in using ATCSs, with approximately 10% not satisfied. SUMMARY This chapter presented the operational backgrounds of ATCS deployments and the institutional capacities of the agencies that deploy ATCSs. In general, agencies deploy ATCSs in operational environments where ATCSs are known to pro- vide the best performance. For most of the agencies, traffic signals under an ATCS contribute from 10% to 30% of the 16 overall signal population under their jurisdictions. Most of the agencies used (although not exclusively) coordinated- actuated control before ATCSs were deployed. Handling daily and weekly fluctuations in traffic flows is the primary reason for ATCS deployments. Most of the agencies, in one way or another, considered multiple ATCSs before they decided which ATCS to deploy. However, only a few of the agencies went through a comprehensive process of reviewing other ATCSs. On average, an ATCS installation takes approximately 18 months, from the time funding is available to the time an ATCS becomes fully operational. Most of the ATCSs (90% to 95%) that were deployed during the last 20 years are still operational. Although the agencies reported various factors that prevented them from expanding their ATCSs, most of the agencies (70%) have expanded their systems since the initial installation. In general, most of the agencies (79%) are satisfied with operations of their ATCSs. The next chapter describes the working principles of ten major ATCSs used throughout the world. Very satisfied; 27; 62% Somewhat satisfied; 8; 18% Neutral; 5; 11% Somewhat dissatisfied; 3; 7% Not satisfied at all; 1; 2% FIGURE 4 Satisfaction of ATCS users with their systems.

Next: Chapter Three - Working Principles of Major Adaptive Traffic Control Systems »
Adaptive Traffic Control Systems: Domestic and Foreign State of Practice Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 403: Adaptive Traffic Control Systems: Domestic and Foreign State of Practice explores the state of practice of adaptive traffic control systems (ATCSs), also known as real-time traffic control systems, which adjust, in real time, signal timings based on traffic conditions, demand, and system capacity.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!