Click for next page ( 11


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

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

OCR for page 10
11 TABLE 2 NUMBER OF SIGNALS OPERATED BY PARTICIPATING AGENCIES No. of Total No. Agency Signals under of Signals 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 11 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 Trnsito, Concepcion, 197 15 Chile 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 33 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 56 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 Greater Manchester Urban Traffic Control Unit, UK 2,200 2,200 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 how ATCS users ranked nine different reasons for deploying The agency served as a testing facility/early deployer such a system. Although there is no reason that is clearly of an innovative signal control method--seven ATCS predominant, one can observe that handling day-to-day and deployments. within-the-day traffic variations was ranked as the most It was recognized that an ATCS would help to resolve important reason for deploying an ATCS. Surprisingly, if conflicts between vehicular traffic and other modes only a single factor with the highest rank for each ATCS (pedestrian, transit, etc.)--five ATCS deployments. deployment is considered then results show that such a sys- There was funding available for capital Intelligent Trans- tem was most frequently deployed because: portation System (ITS) projects and ATCS deploy- TABLE 3 TRAFFIC CONTROL UTILIZED BEFORE ATCS DEPLOYMENT Type of Traffic Control Percent of Agencies Before ATCS Deployment 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.

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

OCR for page 10
13 Other; 4; 9% ACS-Lite; 2; 4% LA ATCS; 2; 4% OPAC; 3; 7% RHODES; 4; 9% SCOOT; 15; 33% SCATS; 15; 34% FIGURE 2 Market shares of various ATCSs. Adaptive Traffic Control System Deployments tants. One of the limitations of the results presented in Fig- ure 2 is that they do not include most of the ATCS deploy- Figure 2 shows the percentages of the ATCSs deployed by the ments in continental Europe. Agencies from that part of the responding agencies; it is noticeable that SCOOT and SCATS world did not show a great interest in participating in the are still the most dominant. However, these results are cor- survey. related to the maturity of the systems and their presence on the market. Although SCOOT and SCATS were developed The installation of an ATCS can be a lengthy and difficult almost 30 years ago, and they have been present in United process. If the network where an ATCS is being installed is States for approximately 15 years, several other systems are in a high-growth area, interaction between ATCS installation much younger. It can also be noted that some of the U.S.- and other ongoing projects may significantly affect installation developed systems have been deployed with support from time. The availability of local consulting, condition of existing the FHWA or similar U.S. federal agencies, whereas most of infrastructure (detection, hardware, and communication), and SCOOT and SCATS deployments were pure commercial proj- availability of funding may all influence the duration of the ects. This dominance of SCOOT and SCATS is further con- installation process. ATCS agencies reported that, on average, firmed among larger ATCS deployments; those having 50 or installation of such a system takes approximately 18 months more intersections under an ATCS. Almost all larger ATCS and is measured from the time when funding is made avail- deployments (except LA DOT) use either SCOOT or SCATS. able until the ATCS is fully operational. Table 5 shows the The major reason for the popularity of SCOOT and SCATS distribution of ATCS deployment times for various installa- may be found in the maturity of these systems and because tion intervals, which range from fewer than 3 months to more they enjoy strong support from their developers and consul- than 2 years. TABLE 5 TIMEFRAMES FOR ATCS DEPLOYMENTS 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

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

OCR for page 10
15 6 Average Median Mode 5 4 Number of staff 3 2 1 0 Engineers Timing technicians Field technicians Maintenance Others technicians Staff category (a) 60 0.6708 y = 0.1973x 2 R = 0.6527 50 40 Number of staff 30 20 10 0 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Number of signals (b) FIGURE 3 (a) Statistics of timings staff; (b) Number of signals versus number of staff.