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APPENDIX A
LITERATURE REVIEW
Traff~c-actuated control has been used since the early i930's. The operational performance of
isolated actuated controlled intersections or a set of coorclinated actuated intersections largely
depends on traffic patterns and actuated controller parameters. A wed-designee! actuated control plan
that responds appropriately to traffic demand can significantly reduce delay and fuel consumption.
Therefore, shortly after actuated signal control was first introduced, researchers began to study the
influence of traffic arrival and departure characteristics at a signalized intersection with traffic-
actuated control. Many researchers also focused on optimizing the controller settings, detector
placement, and the relationship between them. Although more advanced forms of adaptive traffic
control strategies were introduced recently, the original concepts of traffic-actuated control still play
a very important role today.
Review of past and current research is an area that definitely merits attention. There has been a
substantial amount of research conducted on traff~c-actuated control that will contribute to this
project. The main topics of this literature review include:
.
Traffic-actuated control definitions,
Warrants for traffic-actuated control,
Benefits and operating considerations for traffic-actuated control,
Effects of coordination and phase-skipping for traffic-actuated control,
Late-night, low-volume operation of coordinated actuated systems,
Evaluation of traffic-actuated control by simulation,
Estimation of green times and cycle length for traffic-actuated control,
Delay models for traffic-actuated control,
Signalized intersection capacity models for traffic-actuated control, and
Overview and evaluation of "Enhancement of the Value Iteration Program for Actuated
Signals" (EVIPAS).
The procedure contained in the Highway Capacity Manual (HCM) [~] is used almost as a standard
to analyze signalized intersection capacity and level of service, so the major emphasis of this review
is the application to capacity and level of service analysis. One item that needs to be reviewed
carefully is a new program called EWPAS. EVIPAS is an optimization program that analyzes and
determines the optimal settings of timing parameters for traffic-actuated control. The results of the
testing efforts on EV1PAS are reported at the end of this chapter.
TR\FFIC-ACTUATED CONTROL DEFINITIONS
Three basic forms of traffic control: pretested, actuated and semi-actuated were mentioned by Orcutt
[2] in 1975. He indicated that pretimed control was used primarily in the Central Business District
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(CBD) area, especially where a network of signals must be coordinated. He defined actuated signals
in terms of equipment that responds to actual traffic demand of one or more movements as registered
by detectors. If all movements are detected, the operation is referred to as "fully-actuated." If
detectors are installed for some, but not all, traffic movements, the term "semi-actuated" was applied.
Orcutt suggested fi~ll-actuated control should normally be used at isolated intersections.
Precise definitions of the basic controller types were described by the National Electrical
Manufacturers Association ENEMA) standards [3] in 1976. According to the NEMA standards, the
basic controllers include pretimed, semi-actuated, full-actuated without volume-density features, and
full-actuated with volume-density features. In the remainder ofthis discussion, the three types of
traffic-actuated control will be designated as sem~-actuated' fill-actuated and volume-density control.
WARRANTS FOR TRAFFIC-ACTUATED CONTROL
Warrants for selecting traffic control modes, which are very useful for practicing engineers, have been
researched since the early 1960's. Studies of delay at actuated signals have been made with the pur-
pose of evaluating warrants for this type of control based on the 1961 Manual on Uniform Traffic
Control Devices (MUTCD) information. This information was expanded by the Texas Department
of Highways and Public Transportation into a graphical format. The graphical relationships were
studied in 1971 by Vodrazka, Lee and Haenel [4], concluding that they provide good guidelines for
selecting actuated equipment for locations where traffic volumes do not warrant pretimed signals.
The current edition oftheMUTCD stops short of numericalwarrants for choosing between pretimed
and traff~c-actuated control, but it does suggest certain qualitative conditions under which traffic-
actuated control should be implemented.
In 1967, Gerlough and Wagner [5] began to compare pretimed control effectiveness with volume-
density control. They found that traffic-actuated control at higher traffic volumes degraded
performance. One of the problems cited for volume-density control was that the duration of green
for each phase was dependent on the estimated queue length at the beginning of the phase.
Difficulties with queue length estimation made this type of control less effective.
BENEFITS AND OPERATING CONSIDERATIONS
FOR TRAFFIC-ACTUATED CONTROL
Long-loop presence detection operates by producing a vehicle call for the duration of time that the
vehicle is over the detector. On the other hand, small-area detection mode operates by producing a
pulse of less than 0.1 seconds when the vehicle is first detected. The latter mode of operation is
known as passage' pulse or count detection. The long-loop presence detector with full-actuated
controllers is known as lane-occupancy control or loop-occupancy control BLOC). LOC operation
occurs when the controller is programmed for initial green interval of zero. Extensions are set either
to zero or to a very low value. There is no need for a non-zero initial interval or minimum green time
because the long loops continuously register the presence of vehicles that are waiting' causing the
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controller to extend the green until the entire queue is discharged. The result is a signal operation
that responds rapidly to changes in traffic flow.
In 1970, Bang and Nilsson t6] compared LOC operation with small area detector (pulse detector)
operation. They concluded that delay was reduced 10 percent ant! stops by 6 percent under the same
traffic conditions with LOC. In 1975, Cnbbins and Meyer t7] compared pulse and presence
detectors. They concluded that the longer the length of the presence detector on the major approach
to the intersection, the longer the delay. They also concluded that the highest intersection travel time
values occurred when either long-Ioop presence or pulse detectors were used on both major and
minor approaches. The Intersection travel time was cleaned here as the average time it takes a vehicle
to pass through an intersection, whether it is stopped or slowed.
Numerous theoretical studies on traffic signal timing were conducted between 1958 and 1970. The
theoretical work on pretimed control by Webster [~] in 1958 and Miller [9] in 1963 has been applied
to the computation of optimum cycle lengths as a function of vehicle amval rates. It has also been
used for evaluating vehicle delay, intersection capacity, probability of stops and so on. These results
were also wed validated through the comparison of field data. In 1969, Newell tI0] and Newell and
Osuma [l I] expanded the body of theory by developing relationships for mean vehicle delay with
both Retimed and actuated control at intersections of one-way streets and intersections oftwo-way
streets, respectively. In reference 10, Newell demonstrated that the average delay per vehicle for an
actuated signal is less than that of a pretimed signal by a factor of about three for intersections of one-
way streets. Reference Il considered intersections oftwo-way streets without turning vehicles. For
the particular vehicle-actuated policy which holds the green until the queue has been discharged, the
vehicle-actuated control will not perform as well as pretimed control when I) flows are nearly equal
on both approaches of a given phase, and 2) the intersection is nearly saturated. This work confirms
Bang's results, previously described.
In 1976, Staunton [12] summarized the work of numerous signal control researchers. In his paper,
the comparisons of delay produced by pretimed and actuated control, as a function of vehicle
volumes, were presented. Staunton demonstrated that fi~-actuated control with 2.5 see extensions
will always be better than the best form of pretimed operation, given optimum settings for all
volumes. Longer values for the extensions can easily degrade actuated control performance. His
conclusions were based on simulation, but the details ofthe detector configuration were not specified.
In view of the 2.5 see extension time, passage detectors were probably used in this study. The
performance estimates from Staunton were supported by Bang [133.
In 1981, Tarnoff and Parsonson [14] compiled an extensive literature review on the selection of the
most appropriate form of traffic control for an individual intersection. Three complementary
approaches were used to evaluate controller effectiveness: I) field data collection using observers to
manually measure vehicle volumes, stops and delay; 2) simulation using the NETSIM mode}
developed by the Federal Highway Administration (FHWA) to evaluate control system performance;
and 3) analytical techniques developed by the research team and other agencies. Following is a list
of the more relevant conclusions from their extensive literature review.
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I. Pretested controllers operate most effectively when the shortest possible cycle length
is used subject to the constraints of providing adequate intersection capacity and
minimum green times for pedestrians and vehicle clearance intervals.
2.
4.
The delay produced by fit actuated controllers is extremely sensitive to the extension
time setting used. In general, shorter gap extensions reduce vehicle delay.
For small area detectors ~ motion or pulse detectors), at low and moderate volumes
when extensions oftwo or three seconds are employed, the use of fit actuated con-
trollers will produce reduced delays and stops over those obtained using pretimed
controllers. When high traffic volumes occur on both main and side streets causing
the controller to extend the green time to the maximum on all phases, the fi~li-actuated
controller wait perform as a pretimed controller, producing comparable measures of
vehicle flow.
The relative effectiveness of the various control alternatives depends on the quality
of the signal timing employed. A poorly timed actuated controller will degrade traffic
performance to as great an extent as a poorly timed pretimed controller.
Through the detailed evaluation of controller performance, the conclusions by Tarnoff and Parsonson
[14] are descnbed as follows: Sern~-actuated controllers produce a higher level of stops and delays
for ad traffic conditions than either the full-actuated or pret~med controllers. However, for side
streets operating traffic volumes less than 20 percent lower than main street volumes, the difference
in effectiveness between sem~-actuated and fi~-actuated controller is insignificant. FuD-actuated
controllers operating in an eight-phase dual-ring configuration produce significant operating benefits
over the four-phase pretimed controller operation.
Simulation results on small area detectors showed that for approach speeds of 3 5 mph and a 2-second
vehicle interval, locating the detectors farther apart Dom the stop line (150 h) produced a much better
performance level. Tarnoff and Parsonson concluded that it is appropriate to locate the detector such
that the travel time is equal to the extension time. It was also concluded that for volumes in excess
of 450 vehicles per hour per lane and approach speeds of 35 mph or higher, additional improvement
can be achieved through the use of the added initial volume-density controller feature.
They indicated that further moclest gains in performance for full-actuated control were possible with
the use of long loops and short (or zero) initial and extension settings. This application was found
to produce a performance similar to a two second extension time with a short loop. From the
s~rnulation results, they also concluded that LOC was more effective than pulse detection over a wide
range of traffic volumes. LOC offers another advantage not reflected by the simulation results:
_
~ · . · · . . . . . . .. . , . . ~
screening out false calls caused by vehicles approaching but not traveling through the intersection.
Volume-density controllers provide the greatest benefit at intersections with high approach speeds
and detector setbacks in excess of 125 ~ from the intersection. This situation requires a variable
initial green time. Tarnoff and Parsonson found that the t~me-wait~ng and extension-reduction options
AppendixA: Page 4
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ofthe volume-density control clid not improve the controllers perfonnartce over that of a fi~-actuated
controller unless the option is used to reduce the vehicle extension to a value that is less than the one
used for the fi~-actuated controller. Thus, if the volume-density controller is timed to provide a
three-see passage time and a two-see minimum extension, its performance wait be superior to that of
a fi~-actuated controller with a constant three-see extension.
It should be noted that Tarnoff and Parsonson's simulation results do not properly account for the
problem of premature termination of green resulting from the variation in oueue discharge headwavs
that occur under normal operating conditions.
In 1985, Lin [15] studied the optimal timing settings and detector lengths for full-actuated signals
operating in presence mode using the RAPID simulation model. He suggested that the optimal
maximum green for hourly flow patterns with a peak hour factor of I.0 was about ten see longer than
the corresponding optimal greens with a peak hour factor of 0.85, and that the optimal maximum
green was approximately 80 percent longer than the corresponding optimal greens. This result was
similar to the I.5 times pretimed split suggested by Kell and Fulderton [161. I~in indicated that optimal
vehicle intervals were a function of detector length and flow rate. For detectors 30, 50 and 80 Bc
long, the use oftwo-second, one-second and zero-second vehicle intervals can lead to the best signal
performance over a wide range of operating conditions, respectively. The use of vehicle intervals
greater than zero see for detectors 80 feet or longer is not desirable unless the combined critical flow
at an intersection exceeds 1,400 vph.
In order to improve the V]PAS model, a new optimization algorithm and a new intersection
simulation were designed and programmed. The original V1PAS traffic characteristics and vehicle
generation routines were combined with these new models to create the enhanced version called
EVIPAS. In 1987, Bullen, Hummon, Bayer and Nekmat [17] developed EVIPAS, a computer mode}
for the optimal design of a vehicle-actuated traffic signal. - The EVIPAS mode] was designed to
analyze and optimize a wide range of intersection, phasing, and controller characteristics of an
isolated, fi~ly-actuated traffic signal. It can evaluate almost any phasing combination available in a
two to eight-phase NEMA type controller and similar phasing structures for a Type 170 controller.
They indicated that the mode} can provide optimum timing settings for pretimed, sem~-actuated, fi~-
actuated, or volume-density control using a variety of measures of effectiveness chosen by the users.
The mode} has been field tested and validated.
In 1987, Messer and Chang tIS] conducted field studies to evaluate four types of basic full-actuated
signal control systems operating at three diamond interchanges. Two signal phasing strategies were
tested: a) three-phase and b) four-phase with two overlap. Two small-Ioop (point) detection patterns
(single- and multi-point) were evaluated for each type of phasing. They concluded that I) single-
point detection was the most cost-e~ective three-phase design; and 2) multi-point detection was the
more delay-effective four-phase configuration. Four-phase control characteristically operates a longer
cycle length than the three-phase for a given traffic volume. This feature may produce higher average
delays unless the cycle increase is controlled to the extent that the internal progression features of
four-phase can overcome this deficiency.
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In 1989, Courage and Luh [19] developed guidelines for determining the traffic-actuated signal
control parameters which would produce the optimal operation identified by S0AP84. They also
evaluated the existing signal control parameters on an individual traffic-actuated signal. The
significant conclusions are summarized as follows:
Under low volumes, the maximum green settings have little or no effect on the performance of
actuated signal controllers. Under moderate volumes, shorter maximum greens increase the average
delay considerably. Longer maximum greens, however, have no significant effect on delay. Under
high volumes, the maximum green settings become more important. There is a setting which
minimizes average delay. Other settings with longer or shorter greens will produce more average
delays.
The optimal maximum green setting can be achieved by running SOAP under actuated control with
an optimal saturation level set in the BEGIN card. They indicated that the settings which are optimal
at some time may not be appropriate in other times of day. The value of 0.95, which is the default
value used in SOAP actuated control, was suggested for multiphase operation and a slightly higher
saturation level may be desirable for two phase operation. For approaches with a reasonably even
distribution of traffic volume by lane, settings of 4.0, 2.0 and 1.4 seconds were recommended for 1,
2 and 3 lane approaches as the best values for extension, respectively.
In the same year, Bullen [20] used the EV]PAS simulation and optimization model to analyze traffic-
actuated traffic signals. The variables studied were detector type and placement and the settings were
minimum green and vehicle extension. The evaluation criterion was minimum average vehicle delay.
The study showed that the optimum design of a traffic-actuated signal was specific for some variables
but relatively unaffected by others. The design was critical only for high traffic volumes. At low
volumes, vehicle delay is relatively unaffected by the design parameters studied in his paper. The
most critical variable Bullen found was vehicle extension, particularly for passage detectors, where
it should be at least 4.0 seconds regardless of detector placement and approach speed. This
conclusion somewhat contradicts previous study results. However, it should be noted that the model
(EV1PAS) used by Bullen considered variable queue discharge headways.
Detector configuration is essential to the success of actuated control. Kell and Fullerton [21] in their
second edition ofthe Manual of Traffic Signal Design in 1991 indicated that the small area detector
might ideally be located three or four seconds of travel time back from the intersection, with the
allowable gap set accordingly. Similar principles were proposed in previous research by Tarnoff and
Parsonson. Kell and Fullerton also indicated that, in some states, the detector setbacks were
determined based on the safe stopping distance. The main purpose is to avoid the dilemma zone in
which a vehicle can neither pass through the intersection nor stop before the stop line. For long loop
detectors, they indicated that the concept of 100D occupancy control can provide good operation
~· ~. 1' ~1 ~'
. , ~. _
when vehicle platoons are wen torrnea. 1ne use of several smaller loops instead of one long loop was
~ . ~ .1 1 ~ ~ ~
suggested to solve the problem or random vehicles causing excessive green.
In 1993, Bonneson and McCoy [22] proposed a methodology for evaluating traffic detector designs.
They indicated that the safety and efficiency of a traffic detector design can be determined by the
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probability of max-out and the amount of time spent waiting for gap-out and the subsequent phase
change. The stop line detector and advance loop detector with presence and pulse mode were
discussed, respectively. The methodology presented by Bonneson and McCoy determined the
optimal combination of design elements in terms of safety (via infrequent max-out) and operations
(via a short waiting time for phase change). The design elements included detector location, detector
length, vehicle speed, passage time settings, and call extension setting. They concluded that a large
maximum allowable headway will have an adverse effect on performance by increasing the max-out
probability and the length of wait for phase change.
EFFECTS OF COORDINATION AND PHASE-SKIPPING
FOR TRAFfIC-ACTUATED CONTROL
.
In 1986, lovanis and Gregor [23] studied the coordination of actuated arterial traffic signal systems.
In the past, all existed optimization methods required that each actuated signal be converted to its
nearest equivalent pretimed unit. Using bandwidth max~rruzation as a starting point, a new procedure
was developed by Jovanis and Gregor that specifically accounts for actuated timing flexibility. Yield
points and force offs at non-cntical signals are adjusted so they just touch the edges of the through-
band while critical signals are unmodified. This method was applied to a data set describing m~d-day
traffic conditions on an urban arterial system of six signals in central Illinois. Simulation was used
to evaluate these timing plans and compare them with corresponding pretimed alternatives. They
were surprised to find out that pretimed, coordinated control appeared superior in general to actuated
coordinated control in this experiment. They also concluded that the level of service ~OS) of side
streets were much more important for pretimed than actuated strategies.
In 1989, Courage and Wallace [24] developed guidelines for implementing computerized timing
designs from computer programs such as PASSER Il. TRANSYT-7F and AAP in arterial traffic
control systems. The coordination of a group of traffic-actuated signals must be provided by some
forest of supervision which is synchronized to a background cycle length with splits and offsets
superimposed. Both external and internal coordination of the local controllers were addressed.
This report focused on the external coordination oftraffic signal controllers. Permissive periods were
introduced to indicate the time interval following the yield point during which the controller is
allowed to yield to cross street demand. If the computed splits are longer than the minimum phase
times, it might be possible to establish a permissive period without further sacrifice or compromise
on the rest ofthe sequence. The methodology of computing permissive periods was described. The
effect of phase-skipping due to lack of traffic demand was also presented. The Timing
Implementation Method for Actuated Coordinated Systems (TIMACS) program was developed to
perform permissive period computations.
Since most previous studies were more specific to certain geometric and phasing combinations, the
qualitative and quantitative evaluation methodology for coordinated actuated control needed to be
fully investigated. In 1994, Chang and Koothrappally t25] designed a field study to demonstrate the
operational effectiveness of using coordinated, actuated control. They concluded: I) There was
AppendixA: Page 7
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significant improvement, based on both delay and number of stops, between the semi-actuated
control, full-actuated, and pretimed coordinated timing during the study; 2) There were no significant
differences In performance among all the sem~-actuated operations as long as the progression-based
signal coordination timing was developed correctly; and 3) The use of longer coordination cycle
lengths generally caused less arsenal stops. However, it would generate much higher overall system
delays.
LATE-NIG~:T~ LOW-VOL~ OPERATION
OF COORDINATED ACTUATED SYSTEMS
Coordinating the timing of adjacent signals to promote progressive traffic movement was recognized
as one ofthe most effective means for reducing vehicular stops, delay, fuel consumption, and exhaust
emissions. Early efforts on the subject of signal control always indicated the need to interconnect
signals into a single system and to work toward maximizing progressive movement during peak
periods. In 1990' Luh and Courage [26] evaluated the late-night traffic signal control strategies for
arterial systems. They stated that late-night, low-volume arterial signal control involved a trade-off
between the motorists on the artery and those on the cross street. The conventional measures of
effectiveness such as stops, delay, and fuel consumption were not appropriate for evaluating this
trade-off. Luh and Courage proposed a methodology to choose between coordination and Dee
operation on arterial roadways controlled by semi-actuated signals when traffic is light. The choice
was made on the basis of a disutility Unction that was a combination of the number of stops on the
artery and the average cross-street waiting time. The results indicated that this method provides a
promising tool for late-n~ght arterial signal control.
EVALUATION OF TRAF1?IC-ACTUATED CONTROL BY SIMULATION
Simulation modeling has become an extremely important approach to analyzing complex systems.
After 1980, more and more simulation modeling was used in traffic operations. In 1984, Lin and
Percy [27] investigated the interactions between queuing vehicles and detectors for actuated controls,
which govern the initiation, extension, and termination of a green duration. They emphasized that
the model used in the simulation analysis should be calibrated in terms of observed characteristics
such as queue discharge headway, arrival headway, the relationship between the arrival time of a
queuing vehicle and the departure time of its leading vehicle, the number of queuing vehicles in a
defined area at the onset of a green duration, and the dwell time of a vehicle on the detection area.
They also indicated that under a presence control, the chance for premature termination of a green
duration increases when detector lengths are shortened, and a detector length of longer than 80 fit can
effectively eliminate the premature termination. Using long detectors, however, results in longer
dwell times and may reduce control efficiency. Lin and Shen [28] also indicated that the modeling
of the vehicle-detector interactions should take into account the stochastic aspects of queuing in
relation to detectors. The use of average characteristics of departure headway could result in
underestimates or overestimates of the probability of premature termination of the green.
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Later, Fin t29] evaluated the queue dissipation simulation models for analysis of presence-mode fiull-
actuated signal control. The queue dissipation models used in the NET SIM program and the Value
Iteration Process--Actuated Signals (V1PAS) program were evaluated. He indicated that both models
were capable of producing realistic departures of queuing vehicles from the detector area. The
models were rather weak, however, in representing other aspects of vehicle-detector interactions.
A major weakness of the mode} used by NET SIM was that the simulated movements of queuing
vehicles have little to do with the discharge times generated separately from a probability distribution.
The weakness of V1PAS was that the University of Pittsburgh car-follow~ng mode} used in V1PAS
did not provide a flexible model structure for calibration. Therefore, the outputs of the mode! could
not be made to conform easily and simultaneously with observed departure, arrival, and dwell
characteristics of queuing vehicles.
hn 198S, Chang and Williams [30] investigated the assumption that independent vehicle arrivals at
traffic signals, such as in the Poisson distnbution, have been widely used for modeling delay at urban
intersections. The study introduced an effective yet economic approach to estimate the degree of
correlation among among vehicles under given conditions and geometric characteristics. With the
proposed technique, traffic professionals can easily determine if the existing delay formulas and other
traffic simulation models based on the Poisson distribution are applicable.
The presence of high variability in traffic simulation results often leads to concern about their
reliability, and consequently precludes a rigorous evaluation of the target traffic systems performance
under various control strategies. In 1990, Chang and Kanaan [3 1] presented the variability assess-
ment for TRAF-NETSIM. The batch-means method, which allows the user to assess the variability
of parameters, such as the average delay per vehicle, through a single relative long run, was
introduced. This study provided a good contribution to traffic simulation users, given the large
expenditures on computer simulation.
ESTIMATION OF GREEN TIMES AND CYCLE LENGTH
FOR TRAFFIC-ACTUATED CONTROL
Traffic-related phenomena at a signalized intersection, such as lane capacity, delay and queue length
are influenced by the phase times and cycle length. For traff~c-actuated control, green split and cycle
length fluctuate with respect to the traffic demand. Consequently, it becomes desirable to predict the
average green times and cycle length. In 1982, Lin [32] began to develop a mode! to estimate the
average phase duration for full-actuated signals. The mode} was developed primarily on the basis of
probabilistic interactions between traffic flows and the control system. He assumed the arrival at the
upstream side of an intersection would be random' so the arrival pattern in each lane was represented
by a Poisson distribution. Later, Lin and Mazbeyasna t33] developed delay models for semi-actuated
and fi~-actuated controls that employ motion detectors and sequential phasing. These models were
based on a modified version of Webster's formula. The modifications included the use of average
cycle length, average green duration, and tvvo coefficients of sensitivity reflecting the degree of delay
sensitivity to a given combination of traffic and control conditions. In 1990, Lin [34] proposed an
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.
improved method for estimating average cycle lengths and green intervals for semi-actuated signal
operations as mentioned before.
In 1994, Akcelik [35,36] proposed an analytical methodology for the estimation of green times and
cycle time for vehicle-actuated signals based on the bunched exponential distribution of amval
headway. The discussions in his papers were limited to the operation of a basic actuated controller
that used passage detectors and a fixed gap time setting. Both fi~-actuated and sem~-actuated
control cases were studied. A discussion of arrival headway distributions was presented since the
estimation of arrival headways is fundamental to the modeling of actuated signal timings. The
fonnulae were derived to estimate the green times and cycle tune based on the bunched exponential
distribution of arrival headway.
The bunched amval mode} was proposed by Cowan [37] and used extensively by Troutbeck
[3S,39,40,4l,42,43] for estimating capacity and performance of roundabouts and other unsignal~zed
intersections. The bunched arrival mode} considers that the bunched relationship between vehicles
increases when the flow arrival rate increases. Since the bunched arrival mode! appears to be more
representative of real-life amval patterns in general, Akc,elik used this arrival mode! for deriving
various formulae for the analysis of traffic-actuated signal operations. The random amval mode!
which uses negative exponential or shift negative exponential distribution of arrival headway can be
derived as a special case of the bunched arrival mode} through simplifying assumptions about
bunching characteristics of the arrival stream. The methods given in his papers provide essential
information (average green times and cycle length) for predicting the performance characteristics
(capacity, degree of saturation, delay, queue length and stopped rate) of intersections.
DELAY MODELS FOR TRAFFIC-A CTUA1~D CON 1 HOL
With the increase of computer software, the comparison of different traffic programs for pretimed
and actuated controls became intuitively appealing. In ~ 974, Nemeth and Mekemson [44] compared
the delay and filet consumption between deterministic Signal Operations Analysis Package (SOAP79)
and the microscopic and stochastic Network Simulation Mode! (BETSY for pretimed and actuated
controls. They indicated that in terms of delay prediction, SOAP79 and NETSIM were found to be
entirely compatible except for the difference in clelay definitions.
In 198S, Akcelik [45] evaluated the 1985 HCM [~] delay formula for signalized intersections. He
stated that the HCM formula predicted higher delays for oversaturated conditions. An alternative
equation to the HCM formula was proposed. This formula gave values close to the HCM formula
for degrees of saturation less than I.0, and at the same time, is similar to the Australian, Canadian,
and TRANSYT formulas in producing a delay curve asymptotic to the deterministic delay line for a
degree of saturation greater than I.0.
The signalized intersection methodology presented in the 1985 HCM [~] introduced a new delay
model. Lin [46] evaluated the delay estimated by the HCM with delay observed in a field study in
1989. Some inconsistency existed in the delay estimation between the HCM results and the field
AppendixA: Page 10
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observation. He suggested improving the progression adjustment in the HCM procedure and using
a reliable method to estimate average cycle lengths and green durations for traffic-actuated signal
operations.
~ 1989, Hagen and Courage [47] compared the HCM [~] delay computations with those performed
by S0APS4 and TRANSYT-7F Release 5. The paper focused on the elect of the degree of
saturation, the peak-hour factor, and the period length on delay computations and the treatment of
leer burns opposed by oncoming traffic. They indicated that all ofthe models agreed closely at volume
level below the saturation point. When conditions become oversaturated, the models diverged;
however, they could be made to agree by the proper choice of parameters. The computed saturation
flow rates for led turns opposed by oncoming traffic also agreed closely. However, the treatment of
protected plus permitted left turns produced substantial differences. It was concluded that neither
SOAP nor HCM treats this case adequately.
A delay mode} was recommended in the HCM tI] for level-of-serv~ce analysis at signalized
intersections. The use of this mode} for the evaluation of traffic-actuated signal operations required
a knowledge of the average cycle lengths and green intervals associated with the signal operation
being analyzed. Since the method suggested in the HCM to estimate delay of traffic-actuated signal
operations was not reliable, Lin [34] proposed an improved method for estimating average cycle
lengths and green Intervals in 1990. The method was limited to sem~-actuated signal operations. Din
stated that this method, which was developed through analytical modeling and computer simulation,
was .~fficient~v s~mnIe and reliable Realistic examples were used to illustrate the application of the
method.
In 1993, IN Rouphail and Akcelik [48] presented an approach for estimating overflow delays for lane
groups under traffic-actuated control using the 1985 HCM delay mode} format. The average cycle
lengths and green times used in the delay mode! were obt-a~ned Dom a cycle-by-cycle simulation
model. This study was limited, however, to two phase single lane conditions. The results indicated
that the average cycle and green times are very much related to the controller settings such as
mrnimum and maximum green times, cycle lengths, and extension times, with longer extension times
producing higher cycle length. It was found that overflow delay increases with longer extension
times. Further, by applying the 1985 HCM delay formula to the simulated signal settings, the com-
puted delays were much higher. This implies the need for separate calibration of the second delay
term to account for the actuated control effects.
SIGNALIZED INTERSECTION CAPACITY MODELS
FOR TRAFFIC-ACTUATED CONTROL
Intersection capacity analysis is essential for measurements of most traffic control effectiveness. The
first U.S. HCM (1950) contained a chapter for estimating the capacities of signalized intersections.
Numerous studies were undertaken to evaluate the different aspects of signalized intersections and
many capacity methods were developed. In 1983, May, Gedizlioglu and Tai t491 began the evalua-
tion of eight available methods for capacity and traffic-perfo~mance analysis at signalized intersections
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including pretimed and actuated controls. The eight methods included the U. S. Highway Capacity
Manual method (1965), the British method (1966), the Swedish method (1977), the Transportation
Research Board (TRY) Circular 212 planning method (1980), the TRB Circular 212 operations and
design method (19SO), the Australian method (198I), the National Cooperative Highway Research
Program (NCHRP) planning method (1982), and the NCHRP operations method (1982). They
concluded that the NCHRP operations method and the Australian method were found to be the most
cost-effective methods.
In 1991, Prevedouros [50] studied the traffic measurements and capacity analysis for actuated signal
operations. In chapter 9 of the 1985 HCM, he thought it was not appropriate to treat the pretimed
and actuated controls identically, especially concerning the estimation of capacity and performance
of existing Intersections. The study verified the fact that intersections with traffic-actuated signal
controls demand special treatment when estimating their capacity and performance. The main sources
of error and their potential impacts were presented. He developed a comprehensive data collection
and analysis methodology which complemented the procedure in the 1985 HCM. The major findings
were: I) the g/C ratio should be estimated Tom a consistent and complete series of field measure-
ments if accurate results are to be obtained; 2) the true peak hour and peak ~ 5-minute period can be
identified only when cycle-by-cycle data are used; 3) small variations of the peak period of analysis
around the standard length of ~ 5 minutes have a negligible impact on the delay estimation.
OVERVIEW AND EVALUATION OF EVIPAS
EV1PAS is an opti~zation/simulation mode! for actuated controlled, isolated intersections. It is
capable of analyzing and determining the optimal settings of timing parameters for a wide range of
geometric configurations, detector layouts, and almost any phasing pattern available in a single or
dual-ring NEMA and Type 170 controllers. It wait generate the optimized timing settings for
controllers ranging from pretimed to volume-density actuated controllers. The optimum settings of
timing parameters include minimum green time, maximum green time, unit extension time, minimum
gap, time before reduction, time to reduce, added initial, and maximum initial for each phase.
The value of optunal timing is defined as the timing setting which results in the minimum "total cost."
The mode! allows the user to define the total cost to include a variety of measures of effectiveness,
such as delay, filet consumption, depreciation, other vehicle costs and emissions. The POPPAS
mode! allows for two modes of operation. In its optimization mode, the mode! is used to obtain
optimal timing settings by a multivariate gradient search optimization module and an event-based
intersection m~crosimulation. In the simulation mode, EV1PAS allows the evaluation of a
prespecified signal plan just by m~crosimulation.
The input data for the EVIPAS mode! is in text fo~.~at, organized into two separate input files. To
facilitate the use of EV1PAS, a more fiiendly input processor called EZV1PAS [5 I], was developed.
The purpose of EZV1PAS is to ease the data input effort and eliminate coding errors. The input data
is provided by EZV1PAS to the EVE?AS mode! via two text files: a DAT file and a RUN file. Each
file consists of a number of record groups. The data on the DAT file consists mostly of geometric
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data and other data elements which typically remain fixed throughout multiple EVIPAS runs to
analyze various operational features of the study site. The RUN file consists mostly of the
signalization, timing and optimization data.
In DAT files, separate screens are provided for:
Identification and Default Ovemdes, one screen.
Approach Information, one screen.
· Lane and Detector Information, one screen per approach.
Signal System Setup, one screen.
Signal Phasing Definition, one screen.
Period Definition, one screen.
Traffic Volume, one screen per period.
Pedestrian Flow, one screen.
In RUN files, separate screens are provided for:
· Run Control, one screen.
· Cost and Emission Parameters, one screen.
· Signal Timing Start Values, one screen.
Optimization Flags, one screen.
· Lower and Upper Bounds for Optimized Parameter, one screen per EV]PAS signal
section.
.
The EVIPAS model output can be classified into four groups consisting of I) input data echo tables,
2) summary of vehicle generation, 3) summary of optimization progress, and 4) summary of
performance output. For the capacity and level of service oftraffic-actuated control, the performance
outputs are primarily concerned. The summed of performance output is a set oftables reporting the
final results of the EV1PAS simulation/optim~zation run and consists of I) summary of delays table,
2) signal performance summary table, 3) summary of final signal setting table, and 4) sumunary of final
costs table. For this study, summary of delays table and signal performance summary table are more
concerned. The summary of delay table provides delay statistics for the intersection and for each
approach and lane. The signal performance summary table shows the average phase length and
average cycle length. All above delay measures, average phase length, and average cycle length are
based on the m~crosimulation results.
Since EV]PAS is a simulation-based model, it becomes necessary to compare the simulation results
from EV1PAS with other simulation programs. NET SIM is an appropriate candidate for this
purpose. The current version of NETSIM produces very detailed tables of several performance
measures. It does not, however, provide sufficient information on the operation of the controller
itself in the standard output tables. To obtain this information, it was necessary to develop a
postprocessor to extract the operational data from special files used to support the animated graphics
features of NETSIM. The actuated-controller data for each second of operation are recorded and
stored in a text file that is given a file name extension of ".F45" by NETSIM. Through the CNVX45
program, the .F45 file can be converted to a readable .X45 text file. A postprocessor was developed
to read the .X45 file and produce a summary of the operation. The postprocessor has been called
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"NETCOP" for "NETSIM Controller Operation Postprocessor." It can provide phase-specific
infonnation such as percent skipped, percent gapout, percent maxout, average phase time, average
cycle length, and adjusted cycle length. The "Adjusted Cycle Length" is computed by subtracting the
number of seconds of awed (i.e., the time during which no demand was registered on any phase) from
the total number of seconds simulated before dividing by the number of cycles.
Although the simulation techniques used in EV]PAS and N.ETSIM maY differ in some decrees
~ · , · ~ . - ~
theoretically, the phase time estimations tor the same traffic conditions, geometric con~gurat~ons and
actuated timing settings should be close. Thus, the evaluation of EV1PAS was performed by
comparing its simulated phase times with the phase times produced by NET SIM. A total of 15 HEM
hypothetical traffic-actuated examples were used. These examples cover both two-phase and multi-
phase actuated operation. Results Dom the phase time comparison between EV]PAS and NETSIM
are shown ~ Figure Art.
70
U 60
C)
._
al
40:
lo 30
._
En 2°~
cc
10
50
_ ,, ,, , ,,,,,,, , , ,,,,,,, , ,. _ __ _.-.- _ ·-- 7
2
R = 0.96
· icy
_ ~
~ ,~
a~' a3~-
EW''-'''''-----'''':----''''''''--'''-''''''''''''''''''''''''''''''-'''--'---'''''''''''''''''''''''--
o
0 10 20 ~3 ~ 50 60 70
NETSIM Simulated Phase Time (see)
Figure AM Phase time comparison between EV1PAS and NETSIM
A simple regression analysis between the above two simulated phase times was performed and a 0.96
coefficient of determination, R2, was achieved. As expected, the simulated phase times Dom EV1PAS
are very close to those Dom NET SIM simulations. This suggests that, when estimating phase times,
the EVIPAS mode} is as effective as the NET SIM model.
AppendixA: Page 14
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Appendix A: Page 18
Representative terms from entire chapter:
research record
