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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
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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
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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.
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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.
