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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
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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 Tránsito, 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.
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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 agencyís 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.
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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
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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
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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.
