Click for next page ( 2

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 1
ADAPTIVE TRAFFIC CONTROL SYSTEMS: DOMESTIC AND FOREIGN STATE OF PRACTICE SUMMARY Adaptive Traffic Control Systems (ATCSs) adjust, in real time, signal timings based on the current traffic conditions, demand, and system capacity. The systems require extensive sur- veillance, historically in the form of pavement loop detectors, and infrastructure that allows for communication with the central and/or local controllers. Although there are at least 25 ATCS deployments in the United States, these systems may not be well understood by many traffic signal practitioners in the country. Their operational benefits have been demonstrated, but there are still some reservations among individuals in the traffic signal community. These systems are considered expensive and complex and they require high maintenance of detectors and communications. Although a few short surveys have been done, there has been no compre- hensive survey that has addressed major problems with ATCS implementations. The study methodology included three sequential efforts. The first focused on the selection of ATCSs, which are typically deployed in the United States (and worldwide), and identifica- tion of ATCS agencies that could be interviewed. The next effort was to conduct a literature review and gather as much information as possible about ATCS operations and deploy- ments from previous studies. Finally, two electronic surveys were conducted: a shorter e-mail survey for ATCS vendors and a longer web-based survey for ATCS users. Responses were obtained from 34 of 42 agencies in North America, an 81% response rate. Also, responses were obtained from 11 agencies in other countries. Municipal and county traffic opera- tions agencies were the primary contributors among the 45 agencies that responded to the survey. Survey responses indicated that handling daily and weekly fluctuations in traffic flows is the major reason for ATCS deployments. When procuring an ATCS, agencies frequently consider multiple systems. On average, an ATCS installation takes approximately 18 months, from when funding is first available to the time the ATCS becomes fully operational. Most of the ATCSs that have been deployed during the last 20 years remain in operation. Agencies frequently expand their ATCSs and, in general, most of them are satisfied with their ATCS operations. Review of the most widely used ATCSs has shown that various systems use similar strate- gies to cope with fluctuations in traffic demand and distribution. However, each tool is unique and without side-by-side comparison it is difficult to compare the algorithms and adaptive logic of the various tools. Field implementations of various tools are even more unique than their logics, which makes side-by-side field evaluations very expensive and therefore imprac- tical. For this reason, among others, there are few studies available in the literature that doc- ument that the operational concepts of one particular ATCS are better than another. ATCSs are considered more operationally demanding than conventional traffic signal systems, yet agencies are not able to support these systems in the same way they support the conventional systems. Unlike conventional systems that are maintenance-intensive, ATCSs require much more emphasis on the expertise necessary to execute their sophisticated oper- ations. This switch in the type of labor (from maintenance to operations), which is needed to support proper ATCS operations, is often not recognized in the early stages of ATCS

OCR for page 1
2 procurements. An agency's inability to recognize a shift in the necessary labor requirements may cause some disappointment at the agency, and in the long term it may discourage an agency from expanding existing systems or from procuring a new ATCS. There is a need for expertise for successful ATCS implementation. Although many agen- cies implement ATCSs to reduce labor-intensive maintenance of signal timing plans, survey respondents indicated that ATCSs are only tools for traffic management, and they need to be supervised and controlled by skilled engineering staff. Proper training and acquisition and retention of expertise within an agency are reported as the most important factors for allevi- ating institutional barriers for ATCS deployments. ATCS operations are often not perceived as being difficult; however, it appears that ATCS users are rarely given the opportunity to learn how to fully operate their systems. A majority of the ATCS users rely on in-house expertise, which is more an indication of the inadequate resources available to hire outside support than that ATCS users are trained to fully control and operate their systems. Most ATCS agencies do not have financial resources to acquire comprehensive training for ATCS and most are short-staffed. Detection requirements for ATCS are somewhat higher than those for conventional traffic- actuated control systems. Most ATCS users are satisfied with the way their systems handle minor detector malfunctions. ATCS users still struggle sometimes with handling ATCS- specific hardware; however, this is primarily an issue that can be resolved with better training of the technical staff. ATCSs mainly operate on Windows-based platforms and are sometimes integrated with one of the available Advanced Traffic Management Systems. Integration with an Advanced Traffic Management Systems, which was formerly rarely done, has become more frequent with recent ATCS implementations. ATCS software is one of the system components that need improvement, as perceived by most users. Interestingly, ATCS users did not find that ATCS communications cause many more problems than communications of conventional traffic control systems. However, communi- cations play a much more important role in ATCS deployments (owing to the need for the frequent exchange of data between field controllers and other elements of the system). For this reason problems with communications are much more pronounced in ATCS operations. The cost of acquiring, maintaining, and repairing ATCS communications represents one of the major operational costs for ATCS users. The survey results showed that ATCS installation costs per intersection are about US$ 65,000, which is higher than reported previously. Interestingly, results showed that ATCSs require less money than conventional traffic signals for physical maintenance. This finding contradicts the common belief within the traffic signal community that ATCSs are known for costly maintenance of their detectors and communications. When ATCSs are evaluated most agencies prefer to hire outside consultants, who mainly perform field evaluations by means of a set of before-and-after studies. A majority of the user evaluations reported that ATCSs outperformed conventional traffic signal systems. When one considers that most of the agencies used (although not exclusively) coordinated-actuated control before ATCSs were deployed, there is no doubt that, in general, ATCSs outperform coordinated-actuated traffic control systems. The benefits of ATCS deployments are not easily observable in oversaturated traffic condi- tions. Although ATCS users have found that their systems may delay the start of oversaturation and reduce its duration, ATCSs are not recognized as a cure-all for oversaturated traffic condi- tions. However, modifications of ATCSs to reduce oversaturation is often beyond the ability of

OCR for page 1
3 ATCS operational users; therefore, there is little evidence that can be used to draw conclusions about ATCSs' performances in instances of oversaturation. Most users do not perceive that the performance of their ATCSs degrade over time. Public education campaigns about ATCS deployments are not particularly common or effective, as indicated by most of the ATCS users. Also, not many of the ATCS agencies conduct public perception surveys. Those agencies that do reported that results from such surveys are sup- portive approximately 50% of the time. ATCS agencies were generally presently surprised by the system's ability to provide what was observed as "efficient operations" and to adjust to within-day and day-to-day traffic fluc- tuations. Negative surprises were mostly related to difficulties in learning how to operate the system and hardware issues (mostly communications). Lessons learned, from hindsight per- spectives, can be summarized in four categories as needs for: Better local support from the vendors, Better planning for in-house operational and institutional support, A good preparation of the infrastructure (detection and communications), and Detailed pre-installation evaluation to estimate the operational benefits of the ATCS. The following represents a non-inclusive list of actions that agencies that plan to deploy ATCSs might consider before making final decisions. However, it can be noted that every single ATCS deployment is idiosyncratic and every agency operates under slightly different conditions. Secure good local support from the vendor: Ask your vendor for dedicated support field staff; insist on local vendor support. Spend more time with the vendor's engineers and make sure they have the required expertise. Keep a more watchful eye on the contractor installing the system. Consider waiting for a fully vendor-supported system rather than a test application. Improve a planning process to avoid operational and institutional issues in-house: Define a region that you want to start with; literature shows that starting with a larger region is better. Allocate more time for debugging and expected technical difficulties. Involve your operational staff in the decision-making process; do not rely only on the steering committee and project management. Involve your staff in the operations and maintenance of the system--as early as you can and as much as your resources allow--as a result, you will be fully independent and acquire expertise earlier. Expect that you will need more engineers and fewer technicians--your labor require- ments will shift from maintenance-intensive to operations-intensive. Have sufficient enough staff to be trained to manage your ATCS network. Prepare infrastructure (e.g., detection and communications) for an ATCS deployment: Plan utilization of your existing equipment--some agencies are better off when retrofitting, others benefit more from installing new equipment. Investigate detection technologies that will provide an acceptable level of reliability and accuracy for your ATCS operations. Ensure that your local control firmware (if new) operates properly under ATCS and that your technicians are comfortable using it. Review and plan reliable and affordable communications. Consider installing other Intelligent Transportation System components to help you monitor your ATCS operations (e.g., closed circuit television cameras). Ensure that ATCS algorithms and adaptive logics will fit your needs; if monitoring queues and oversaturation is your major problem, do not install an ATCS that cannot monitor those parameters and whose logic cannot help you to alleviate your problems.

OCR for page 1
4 If more detection is required, plan your actions and perform a costbenefit analysis to investigate how much detection is needed and what system can be optimal with new detectors. Conduct a detailed pre-installation evaluation to estimate operational benefits of the ATCS before deciding to implement the system: Gather more before-and-after data; make sure that you really need an ATCS-- sometimes a good coordinated-actuated control can be as good as an ATCS. If your intersections have regularly repetitive traffic conditions an ATCS may not be necessary. Run the operations with traffic signals under actuated coordination (if possible) before deploying an ATCS. If extensive capital costs for intersection infrastructure are needed (e.g., geometric re-configuration, replacement of signals, and detection) seriously consider an ATCS-- it will remain in better shape than conventional traffic control regimes in the years to come. Overall, most of the surveyed ATCS users (73%) would install the same system again. Users with more signals under an ATCS have better experiences with ATCS operations. Major reasons that prevent ATCSs from further expansions or new ATCS deployments are high costs related to operating and maintaining an ATCS (e.g., employing and training the staff). More signals under an ATCS attract more attention within the agency, more resources to operate and maintain ATCSs, more staff to develop and maintain in-house expertise, and finally more attention from ATCS vendors. Smaller systems tend to have more problems in securing funding and hence their overall experience with ATCSs is not as positive.