Signal Timing and Incident Management in Small Urban Areas

Abstract

In most metropolitan areas, incident-related delay accounts for about 60 percent of total congestion delay. In small urban areas, it can account for an even larger proportion. A serious problem faced by most small urban areas today is how to handle diverted traffic from an adjacent freeway to local arteries due to an incident. The implementation of Incident Management Systems (IMS) in small urban areas can effectively manage affected traffic through the deployment of Advanced Traveler Information Systems and Advance Traffic Management Systems. Adequate signal timing adjustments on established alternative routes become very crucial to reduce secondary accidents and traffic congestion on both freeway and affected urban arteries. This paper uses six case studies of the Interstate 75 corridor in Sarasota, Florida with implementation of IMS to evaluate alternative route operations associated with signal timing strategies to provide recommendations in response to a freeway incident. The SYNCHRO software was used for the developments of optimal signal timing strategies on alternative routes and SimTraffic microscopic simulation software was used to assess the benefits of alternative route operations. Simulation results show that optimal signal coordination on the alternative route is the best signal timing strategy in small urban areas if informed traffic diversion is determined. It is concluded that one must take traffic conditions on freeway and local arteries, characteristics of alternative routes, reduction of freeway capacity, types of freeway ramps, and estimated incident duration into consideration to provide the best decision and operation of traffic diversion on alternative routes.

Full text

Signal Timing and Incident Management in Small Urban Areas
Pei-Sung Lin, Ph.D., P.E.
Abstract. In most metropolitan areas, incident-related delay accounts for about 60 percent of
total congestion delay. In small urban areas, it can account for an even larger proportion. A
serious problem faced by most small urban areas today is how to handle diverted traffic from an
adjacent freeway to local arteries due to an incident. The implementation of Incident
Management Systems (IMS) in small urban areas can effectively manage affected traffic through
the deployment of Advanced Traveler Information Systems and Advance Traffic Management
Systems. Adequate signal timing adjustments on established alternative routes become very
crucial to reduce secondary accidents and traffic congestion on both freeway and affected urban
arteries. This paper uses six case studies of the Interstate 75 corridor in Sarasota, Florida with
implementation of IMS to evaluate alternative route operations associated with signal timing
strategies to provide recommendations in response to a freeway incident. The SYNCHRO
software was used for the developments of optimal signal timing strategies on alternative routes
and SimTraffic microscopic simulation software was used to assess the benefits of alternative
route operations. Simulation results show that optimal signal coordination on the alternative
route is the best signal timing strategy in small urban areas if informed traffic diversion is
determined. It is concluded that one must take traffic conditions on freeway and local arteries,
characteristics of alternative routes, reduction of freeway capacity, types of freeway ramps, and
estimated incident duration into consideration to provide the best decision and operation of
traffic diversion on alternative routes.
BACKGROUND
Congestion is a growing problem throughout the country. Increased traffic congestion is among
the top two or three factors people cite as having a major impact on their daily lives. According
to a 1999 study by the Texas Transportation Institute (TTI), more than 31% of urban freeways
throughout the country are congested. Traffic congestion costs motorists more than $72 billion a
year in wasted time and fuel costs. Americans waste more than 4.3 billion hours per year stuck
in traffic – approximately 34 hours per driver. TTI also found that traffic congestion is no longer
just a phenomenon of a big city, it grows with an even faster rate in small and medium urban
areas. The largest increase in travel time delay from 1982 to 1997 occurred in small urban areas,
with 400% growth. Furthermore, according to the U.S. Department of Transportation, highway
travel is forecasted to increase about 40% by 2015.
The incident management report from Cambridge Systematics, Inc. indicated that incidents, such
as traffic accidents, stalled vehicles, construction and maintenance, special events, and adverse
weather conditions, account for nearly 60% of all traffic congestion in the United States. In
general, more delay is caused by incidents than heavy traffic demand. Incidents have a
significant effect on delay in areas of all sizes. The small and medium urban areas have a greater
percentage of total delay due to incidents than larger urban areas.

Incidents not only consume precious time, capacity, and economic productivity, they also take
lives. According the Transportation Link newsletter in April 2000, motor vehicle crashes are the
leading cause of workplace death and injury. Nationally, motor vehicle crashes kill 41,000
people and injure 3.2 million more each year. Society spends $150 billion in motor accidents
every year - and the cost to employers is over $50 billion.
Currently, Florida Department of Transportation (FDOT) works diligently with incident
responding agencies of all levels within the state of Florida and consultant companies on
statewide incident management program. Incident management with technologies in Advanced
Traffic Management System (ATMS) and Advanced Traveler Information System (ATIS) on
Interstate 75 (I-75) will be deployed in the near future. With full support from FDOT District
One, Sarasota County Public Works initiated an incident management project in January 2002 in
attempt to effectively manage diverted traffic to local arteries from I-75 and also reduce the total
delays of motorists due to an incident. This study is part of the countywide incident management
project, and mainly focuses in the Sarasota urban area.
Traffic management plays a significant role in the incident management to prevent secondary
accidents and reduce congestion duration for motorists. Establishment of the most applicable
and pre-planned alternative route and adequate modification of signal timing plans on the
alternative route are keys to the success of traffic management in response to a freeway incident,
especially in small urban areas. Continuous traffic monitoring and operational evaluation are
necessary during the whole incident period.
PROBLEM STATEMENTS
Lack of incident related information, deficient alternative route and inadequate signal timing
adjustment are the major complaints from the general public stuck in traffic congestion on a
freeway due to an incident. It is unacceptable for traffic to be stopped because of an incident for
a long period of time without properly routing traffic around the incident. A serious problem
faced by most small urban areas today is how to handle diverted traffic from an adjacent freeway
to local arteries due to an incident. Currently, most small urban areas either do not establish
alternative routes for freeway incidents or do not implement special signal timing plans on
alternative routes to improve traffic flow. As a result, little congestion relief strategy is done in
response to a freeway incident in most small urban areas.
Once an alternative route is established, adequate signal timing plans implemented on the
alternative route are among the most cost-effective activities that small urban transportation
agencies can do to improve diverted traffic flow. It is very crucial to reduce secondary accidents
and traffic congestion on both freeway and affected urban arteries. In the past, incident
management was mainly focused on freeway systems in large metropolitan areas. Few studies
addressed how to design and implement adequate signal timing plans to handle diverted traffic
from a freeway to an alternative route in small urban areas. Therefore, it is essential to have
more understanding on signal timing strategies and alternative route operation in small urban
areas.

INCIDENT MANAGEMENT SYSTEMS AND ITS TECHNOLOGIES
According to the FHWA Traffic Incident Management Handbook, incident management is
defined as the systematic, planned, and coordinated use of human, institutional, mechanical, and
technical resources to reduce the duration and impact of incidents, and to improve the safety of
motorists, crash victims, and incident responders. The purpose of incident management is an
attempt to reduce detection, response and clearance time of an incident, thereby reducing
secondary accidents and total delays experienced by motorists affected by the incident.
Intelligent Transportation Systems (ITS) – the application of advanced sensor, computer,
electronic and communication technologies – provides complementary means to maximize the
efficiency and safety of transportation infrastructure. ITS technologies have been used on
incident management by many large urban areas to provide a faster, safer, and more efficient
response to an incident. Several large metropolitan areas have experienced positive benefit/cost
ratios. A study by Shawn Birst and Ayman Smadi showed that small urban areas could also
benefit from the deployment of ITS technologies on incident management.
ATMS and ATIS are two major components of ITS that provide the most benefits to incident
management. ATMS can be used to quickly detect an incident on freeways, effectively verify
the incident, provide real-time traffic control strategies, divert upstream traffic away from the
incident location, properly adjust signal timing plans on affected intersections and continuously
monitor traffic flow. ATIS can be used to provide incident information, estimated delay
estimation, alternative route information to motorists through variable message signs (VMS),
highway advisory radios, telephone broadcasts and websites. Studies in the literature show that
the implementation of both ATMS and ATIS during an incident is more effective than
implementing only one of them. ATMS and ATIS were used in this study to examine signal
timing strategies and alternative route operations
CONSIDERATIONS NEEDED FOR THE OPERATIONS OF AN ALTERNATIVE
ROUTE AND SIGNAL TIMING ADJUSTMENTS DURING A FREEWAY INCIDENT
It is intolerable for traffic to be stopped on a freeway for a long period of time without properly
routing traffic around the incident. On the other hand, it is not necessary to inform motorists on
a freeway of an alternative route and implement special signal timing plan for a very minor
incident. Several major considerations are needed on the alternative route operation associated
with signal timing strategies during a freeway incident. Three major considerations required for
the later case studies are addressed below. They include duration of a freeway incident,
reduction of freeway capacity and percentage of diverted traffic.
A. Duration of a Freeway Incident
The longer an incident lasts, the more it impacts motorist’s safety and travel time; therefore, the
major effort of incident management is to reduce duration of an incident. Incident duration
includes times for detection, verification, response and clearance. The duration of an incident is
not dependent on any one factor, but rather is the result of many factors working together.

A study conducted at the University of California, Irvine, found the average duration of an
incident is 37 minutes, with a standard deviation of 30 minutes attributable to different
conditions. For example, the study determined that the average duration of a night-time
disablement involving a lane closure was 14 minutes, whereas the average duration of a daytime
injury accident involving lane closures was 66 minutes. Georgia’s NAVIGATOR system is a
highly integrated ITS management system include ATMS and ATIS and other ITS components.
Before the implementation of the NAVIGATOR system, the average duration of incident is 64
minutes, and it was reduced to 41 minutes after the implementation. The Los Angeles County
Metro FSP is a partnership program which was comprised of 149 tow trucks, patrolling 43 beats
(freeway segments), covering more than 400 freeway centerline miles in Los Angeles County.
The average duration of all incidents was 20 minutes. From above information, more than 90%
of freeway incidents are under 100 minutes based on a normal distribution of incident durations.
Therefore, the maximum incident duration of 100 minutes is used in the case studies.
B. Reduction of Freeway Capacity
An incident on a freeway usually will significantly affect the freeway capacity. The more
capacity reduced by an incident, the quicker the traffic backed up. The operation of an
alternative route associated with adjustments of signal timing plans become more urgent.
According to FHWA Traffic Incident Management Handbook, the majority of recorded incidents
were found to involve disable vehicles on the shoulders. Approximately 23% of incidents
blocked lanes. An incident or an unplanned work zone activity reduces freeway capacity by an
amount far greater than the physical reduction in roadway space caused by the incident. As such,
an incident blocking one lane of a three-lane freeway reduces capacity by almost 50%, although
only a third of the lanes are blocked. An incident blocking two lanes of a three-lane freeway
reduces 83% of capacity. Therefore, a freeway incident with two lanes blocked is used in the
case studies to represent a significantly reduction of freeway capacity.
C. Percentage of Diverted Traffic
The percentage of diverted traffic from a freeway to a local artery due to an incident depends on
many factors including freeway condition, congestion level on local arteries, traveler information
received and driver’s preference. The larger percentage of diverted traffic, the greater impact on
local arteries. From system performance perspective, when a freeway is heavily congested and
lots of capacities are still available on local arteries, more diverted traffic may be encouraged. If
the local street is also very congested, high percentage of diverted traffic may make the whole
system worse.
During a freeway incident, an estimated 5% drivers would voluntarily seek a less congested
route in response to the incident. A study conducted by Smith and Perez in 1992, as part of the
INFORMS project, reported that 5 to 10% of motorists would divert given general VMS
message. The diversion percentage doubled when specific diversion routes were provided to the
motorists. In another evaluation of INFORMS shown in Variable Message Sign article updated

in 1998, 45% people said they diverted to an alternative route in response to VMS. A study for a
system-wide evaluation of an integrated traffic control and route diversion strategy by Cuneo,
Jha and Ben-Akiva indicated that when both freeway and alternative routes are at 100% demand,
few vehicles diverted since the alternative route was not significantly more attractive. Birst and
Smadi adopted 20% and 50% diverted motorists in their study of an application of ITS for
incident management in second-tier cities. According the above information and traffic
conditions in Sarasota urban area, 25% of I-75 through traffic are assumed diverted to an
alternative route if motorists receive incident related and alternative route information. 80% of
traffic on local arteries approaching an incident on I-75 are assumed diverted to an alternative
route if the same traveler information is provided.
SCOPE OF STUDY
The incident management activities require the skills and expertise of many diverse disciplines
and agencies. In addition to advanced techniques, the successes of incident management are also
dependent on the cooperation and communication of responding agencies. This study mainly
focuses on the operations of alternative routes and strategies for signal timing plans in response
to a freeway incident. ITS technologies in ATMS and ATIS were adopted to evaluate signal
timing strategies. The intent of this study is to provide recommendations on how to effectively
operate alternative routes and adequately design signal timing plans on these alternative routes in
response to a freeway incident in small urban areas.
OVERVIEW OF METHODOLOGY AND PROCEDURE
This study used a microscopic traffic simulation program, SimTraffic, to evaluate signal timing
strategies on alternative routes in response to a freeway incident. This study first identified the
study area and signal timing strategies for evaluation. Three signal timing strategies includes 1)
no timing change, 2) optimal free operation and 3) optimal signal coordination on an alternative
route. A literature review was then conducted on the deployment of ATIS and ATMS in incident
management. Incident duration and percentage of diverted traffic from a freeway were also
reviewed. Six case studies on the I-75 corridor in Sarasota, Florida are used to simulate a
freeway incident in small urban areas. After the establishment of alternative routes, this study
started extensive data collection including traffic volumes, roadway and intersection geometry
and existing signal timing information. Then, six networks including I-75 and many urban
arteries were constructed. This study properly distributed traffic volumes based on percentage
of diverted traffic and original origin-destination distributions. For each signal timing strategy,
SYNCHRO, one of the most popular signal timing software, was used to develop signal timing
plans on traffic signals on each alternative route. In each case study, SimTraffic simulated
different scenarios associated with signal timing strategies, ATIS and ATMS. For each scenario,
different incident duration periods were used to determine the time to use alternative routes and
special signal timing plans. The final evaluation of signal timing strategies was based the
comparison of the measures of effectiveness (MOE) such as total travel time, total delay and
average speed. It is necessary to note that SimTraffic was chosen as a simulation tool in this
study because it is efficient and convenient to run SimTraffic microscopic simulations after the

signal timing design through SYNCHRO and no extra conversion work or coding needs to be
done in order to run CORSIM. This saves tremendous time to run more than one hundred
simulations in this study. In addition, the results from SimTraffic are very close to CORSIM.
SimTraffic uses many of the same driver and vehicle performance characteristics as CORSIM.
The methodology and procedure used in this study are summarized as follows:
1. Identify the studied area and signal timing strategies for evaluation
2. Perform literature review.
3. Research incident duration and percentage of diverted traffic
4. Establish alternative routes
5. Collect traffic volume, geometry and existing signal timing information
6. Construct networks and perform traffic distribution in the network
7. Develop signal timing plans for each strategy in each case study using SYNCHRO
8. Conduct simulation analysis using SimTraffic
9. Compare MOE of each scenario in each case study
10. Provide conclusions and recommendations
CASE STUDIES
Sarasota is located on the west coast of Florida. It is approximately 50 miles south of Tampa.
With its incredible economic outlook and quality of life, Sarasota was selected as the best small
city by Money Magazine in 2000, and America’s best place to live and work in Employment
Review in the same year. In 2002, the estimated population in Sarasota urban area is
approximately 170,000 and 230,000 during winter season. The size of the county and its
economic perspective make it an ideal example of a small urban area for this study.
The roadway system in Sarasota urban area belongs to a grid system. I-75 is the major north-
south corridor on the east side of Sarasota urban area, while U.S. 41 and U.S. 301 are on the west
side. Several major north-south arteries are in the middle. In the east-west directions, there are
four arteries in Sarasota urban area connecting I-75 and U.S. 41. The roadway network, in case
studies for signal timing strategies on alternative routes, is shown in Figure 1. I-75 is a six-lane
freeway in Sarasota urban area with four freeway-highway interchanges. From north to south,
they are Exits 40, 39, 38 and 37 as shown in Figure 2. In order to design signal timing plans on
established alternative routes for possible freeway incidents on I-75 between Exits 37 and 40, six
case studies listed below were conducted. The alternative route for each case study is shown in
Figure 3.
Case 1: Incident on northbound of I-75 between Exit 39 and Exit 40
Case 2: Incident on southbound of I-75 between Exit 39 and Exit 40
Case 3: Incident on northbound of I-75 between Exit 38 and Exit 39
Case 4: Incident on southbound of I-75 between Exit 38 and Exit 39
Case 5: Incident on northbound of I-75 between Exit 37 and Exit 38
Case 6: Incident on southbound of I-75 between Exit 37 and Exit 38

Figure 1. Roadway Network in Case Studies for Signal Timing Strategies on Alternative
Routes
University Parkway
I-75
Fruitville Road
Bee Ridge Road
Clark Road
Honore Avenue
Cattlemen Road
Honore Avenue
Exit 40
Exit 39
Exit 38
Exit 37
Gantt Road
Proctor Road
N
3.5 miles
2.7 miles
2.0 miles
. --- signal

EXIT 40 EXIT 39
EXIT 38 EXIT 37
Figure 2. Aerial Photos for I-75 Exits in Case Studies

Case 1 Case 2
Case 3 Case 4
Case 5 Case 6
Figure 3. Established Alternative Route for Each Case Study

A. Evaluation Scenarios
Ideally, adaptive traffic control such as SCOOT, SCATS, or RT Tracs should be deployed in
urban arteries to manage unexpected surge of diverted traffic such as a freeway incident;
however, most transportation agencies in small urban areas cannot afford it. Theoretically,
optimal signal timing should be developed and implemented based on real-time diverted traffic;
however, time and data are not always available for traffic engineers to design and implement
optimal timing plans on alternative routes during a freeway incident. A practical way to operate
traffic diversion on alternative routes in small urban areas is to design optimal timing plans for
alternative routes based on typical PM peak traffic volumes (i.e. 100th highest hourly volumes) in
advance and implement them during a freeway incident if needed. Generally speaking, if signal
timing plans on the alternative routes are adequate for traffic diversion from a freeway incident
during PM peak hours, they will be able to provide efficient diversion during off-peak hours.
Proper adjustment on the implemented signal timing plans may be necessary during real traffic
diversion.
In these case studies, it is assumed that the incident occurs midway between two I-75 exits to
represent an average condition. Two lanes of a three-lane I-75 in one direction were assumed
blocked by an incident to represent a significant reduction of freeway capacity. Generally
speaking, in Sarasota urban areas, the roadway level of services (LOS) on I-75, University
Parkway, Fruitville Road and Bee Ridge Road during PM peak hours are D. The LOS for Clark
Road is between B and C because of lighter traffic on a six-lane highway. The LOS for minor
arteries parallel to I-75 used as alternative routes is between B and D. However, they are only
two-lane roadways. In these case studies, traffic volumes during typical PM peak hour (100th
highest hour volume) in 2001 were used for analysis. Based on previous literature review on
percentage of diverted traffic, and traffic condition in Sarasota urban areas during PM peak
hours, this study assumed 25% (range: 600 – 800 vehicles per hour) of I-75 through traffic was
diverted to alternative routes when they received incident-related and alternative route
information through ATIS. Since most drivers on the local artery to I-75 will use alternative
route to avoid I-75 incidents if they obtain the same traveler information through ATIS, this
study assumes 80% (range: 500 – 850 vehicles per hour) of local traffic who originally plan to
use the I-75 section with an incident on their trips will use alternative route.
The following six scenarios shown in Table 1 were used to evaluate the signal timing strategies
on alternative routes in response to incident on I-75. For Scenarios 1 and 2, no ITS deployment
is used. ATIS only is applied for Scenario 3. ATIS and ATMS deployments are adopted in
Scenarios 4, 5 and 6. As to signal timing strategies, existing signal timing plans are used for
Scenarios 1, 2 and 3. Optimal free operation is developed for Scenario 4. Optimal signal
coordination strategies are used for Scenario 5 and 6. Scenarios 1 and 2 use 2001 traffic volumes
and roadway geometry in the microscopic traffic simulation. Scenario 1 simulates normal traffic
condition during typical PM peak hour without an incident, which is primarily used for
validation. Scenario 2 is an incident based case, primarily used for comparison of MOE with
other scenarios. 5% of I-75 through traffic is assumed self diverted to other routes to reflect
actual situation during a freeway incident. Scenarios 3, 4, 5 consider 25% of I-75 through traffic
and 80% of traffic on local arteries approaching an incident on I-75 diverted to an alternative
route if the same traveler information is provided. Scenario 6 explores the situation with only I-
75 traffic diverted to an alternative route.

Table 1. Scenarios for Case Studies
Scenario
ITS Deployment
Signal Timing
Strategy
Traffic Diversion
1. Base
None
Existing timing
None
2. Incident Base
None
Existing timing
Self-diverted from I-75
3. ATIS Only
ATIS
Existing timing
I-75 and local artery
4. Free Operation
ATIS and ATMS
Optimal free operation
I-75 and local artery
5. Coordination
ATIS and ATMS
Optimal signal
coordination
I-75 and local artery
6. Coordination (Only
I-75 traffic diverted)
ATIS and ATMS
Optimal signal
coordination
I-75 only
B. Incident Duration used in Case Studies
The duration of a freeway incident can range from a couple of minutes to several hours. From
previous literature review, it is reasonably to use 100 minutes as maximum incident duration in
this study. Hence, every scenario in six cases was simulated in 20, 40, 60, 80 and 100 minutes
for incident duration. The detection and verification time for an incident blocking two lanes of
urban freeway usually takes only 2 to 3 minutes. Cellular phone reports from motorists make
incident detection much faster, and Closed Circuit TV in Traffic Management Center provides an
effective tool for visual verification. It usually takes 6 to 8 minutes to implement special signal
timing plans on an alternative route and display incident-related and alternative route information
to motorists through VMS or fixed flap signs. Therefore, this study assumes special signal
timings, incident-related and alternative route informations are implemented 10 minutes after the
freeway incident. During the first 10 minutes of the incident, there is no signal timing change for
each scenario in each case studies.
CASE STUDY RESULTS
Based on the microscopic traffic simulation, SimTraffic can provide a simulation summary,
queuing information, actuated timing, and performance report for each simulation run for the
analytical analysis. The results show that the average delay per vehicle in the network increase
dramatically when the incident duration increases. The average delay per vehicle increases 23%,
93% and 204% for incident duration of 20, 60 and 100 minutes respectively. Total travel time in
network also increases significantly. Figure 4 shows the comparison of total travel time for each
case between normal traffic condition (Base scenario) and incident condition without informed
traffic diversion (Incident Base scenario) on the alternative route. The total travel time in the
network increases 3%, 22% and 51% for incident duration of 20, 60 and 100 minutes
respectively. The information on the increase of total travel time or total delays during a freeway
incident can be used to estimate fuel consumption and the productivity loss due to an incident.
Figures 5, 6, 7, 8, 9 and 10 show the relationship of average delay per vehicle and incident
duration under different scenarios for Cases 1, 2, 3, 4, 5, and 6 respectively. The results in Cases

1 and 4 indicate that informed traffic diversion through ATIS to the alternative route is not
always better than self-diversion. Case 6 shows a significant reduction about 25% on average
delay per vehicle in a 100-min incident duration if optimal signal coordination is implemented on
the alternative route with traffic diversion from both I-75 and Bee Ridge Road. Case 2 shows
some benefit and Cases 3 and 5 show little benefit of informed traffic diversion through ATIS
associated with optimal signal coordination strategy. Details on each case study will be
presented in the discussion.
These case studies indicate that the conclusion from one case study cannot directly apply to the
other case because traffic conditions, characteristics of the alternative route, and types of freeway
ramps are different from case to case. However, general rules emerging from the study can be
applied for adequate design of signal timing plans and effective operation of established
alternative routes in response a freeway incident in small urban areas. Optimal signal
coordination on the alternative route is the best signal timing strategy in response to a freeway
incident if informed traffic diversion through ATIS is determined. It is inadequate to give
incident related and alternative route information to motorists without actual signal timing
adjustment on the alternative route (ATIS only). Decision on the operation of alternative route
associated with signal timing adjustment should be based on traffic conditions on freeway and
local arteries, characteristics of the alternative routes, types of freeway ramps, reduction of
freeway capacity, and estimated duration of the incident. When sufficient capacity exists on the
alternative route, more informed traffic diversion is encouraged. From the perspective of system
performance, self-diversion is better when the alternative route and local arteries are heavy
congested.
Figure 4. Comparison of Total Travel Times between Normal and Incident Conditions
C o m p ariso n of To ta l T rav el T im e
0
4000
8000
12000
16000
20 40 60 80 100
In cid en t D u ra tio n (m in )
T ota l Travel Tim e (h r)
B a se
C ase 1
C ase 2
C ase 3
C ase 4
C ase 5
C ase 6

Figure 5. Relationship between Average Delay and Incident Duration for Case 1
Figure 6. Relationship between Average Delay and Incident Duration for Case 2
C ase 1
0
200
400
600
800
1000
20 40 60 80 100
In cid e nt Du ra tio n (m in )
Average Delay (sec/veh)
B a s e
Inc id ent B ase
A TIS O nly
F ree O peration
Co ordin ation
Co ordination (only I-
75 traffic d iverted)
C ase 2
0
200
400
600
800
1000
20 40 60 80 100
In cid e nt Du ra tio n (m in )
Average Delay (sec/veh)
B a s e
Inc id ent B ase
A TIS O nly
F ree O peration
Co ordin ation
Co ordination (only I-
75 traffic d iverted)

Figure 7. Relationship between Average Delay and Incident Duration for Case 3
Figure 8. Relationship between Average Delay and Incident Duration for Case 4
C ase 3
0
200
400
600
800
1000
20 40 60 80 100
In cid e n t Du ra tio n (m in )
Average Delay (sec/veh)
B a s e
Inc id ent B as e
A TIS O nly
F ree O peration
Co ordin ation
Co ord ination (only I-
75 traffic d ive rted)
C ase 4
0
200
400
600
800
1000
20 40 60 80 100
In cid e n t Du ra tio n (m in )
Average Delay (sec/veh)
B a s e
Inc id ent B as e
A TIS O nly
F ree O peration
Co ordin ation
Co ord ination (only I-
75 traffic d ive rted)

Figure 9. Relationship between Average Delay and Incident Duration for Case 5
Figure 10. Relationship between Average Delay and Incident Duration for Case 6
C ase 5
0
200
400
600
800
1000
20 40 60 80 100
In cid e nt Du ra tio n (m in )
Average Delay (sec/veh)
B a s e
Inc id ent B ase
A TIS O nly
F ree O peration
Co ordin ation
Co ordination (only I-
75 traffic d iverted)
C ase 6
0
200
400
600
800
1000
20 40 60 80 100
In cid e nt Du ra tio n (m in )
Average Delay (sec/veh)
B a s e
Inc id ent B ase
A TIS O nly
F ree O peration
Co ordin ation
Co ordination (only I-
75 traffic d iverted)

DISCUSSIONS ON CASE STUDIES
Case 1. Incident on northbound of I-75 between Exit 39 and Exit 40: The scenario of
Incident Base has shown the lowest average delay per vehicle among incident scenarios. This
case indicates self-diversion (Scenario 2) of traffic from I-75 is the best response to a northbound
incident on I-75 between Exit 39 and Exit 40 to reduce the average delay per vehicle in the
network during PM peak hours. As to signal timing strategies, signal coordination with optimal
timing plan is better than free operation with optimal timing plan and no timing change
strategies. From observation of simulation, three major reasons may explain why no official
diversion on established alternative routes through Honore Avenue is the best response. First,
University Parkway carries heavy traffic during PM peak hours although it is a six-lane high-
speed artery. Currently, there is only one eastbound left-turn lane to serve existing heavy
eastbound left-turn traffic to northbound I-75. The existing level of service at University
Parkway and I-75 East Ramp is between E and F. The intersection has limited capacity to serve
heavy diverted traffic. Secondly, the northbound diverted traffic from I-75 needs to travel
through two signalized intersections at both Exit 39 and Exit 40. This causes heavy delay to both
diverted and local traffic. Finally, the major alternative route, Honore Avenue, is only a two-
lane low speed minor artery, which can only carry a small amount of traffic. Since this
alternative route is congested during PM peak hours, the diversion of only I-75 traffic is better
than diversion of traffic from both I-75 and Fruitville Road if traffic diversion is determined.
Case 2. Incident on southbound of I-75 between Exit 39 and Exit 40: This case examines the
signal timing strategies for the alternative route for the southbound I-75 incident between Exit 39
and Exit 40. In this case study, the diversion of traffic to the alternative route with signal timing
adjustment in Scenarios 4, 5 and 6 shows approximately 7% less average delay than that of the
Incident Base in a 100-min incident duration. Free right turn lane from I-75 southbound off
ramp at Exit 40 to a designed lane of University Parkway without stopping at the intersection
makes the traffic diversion from I-75 very effective. Dual southbound left-turn lanes at the
Honore and Fruitville intersection also provide more capacity to this alternative route. It is
another advantage of this alternative route that the diverted traffic returns back to I-75
southbound on ramp without traveling through the signal at the Fruitville and I-75 West Ramp
intersection. In addition, both University Parkway and Fruitville Road are six-lane highways
that make the alternative route more attractive even though Honore Avenue is only a two-lane
minor artery. In this case, the simulation results show the optimal free signal operation is as
effective as signal coordination strategy. The scenario with ATIS only produces the largest
average delays among all scenarios because the existing green time for westbound left turns lane
at University and Honore intersection is too short to handle large diverted traffic from I-75. This
causes immediate traffic back up on the westbound of University Parkway and eventually severe
traffic backup on the northbound of I-75.
Case 3. Incident on northbound of I-75 between Exit 38 and Exit 39: This case explores the
northbound alternative route between Exit 38 to Exit 39 of I-75 from six-lane section of Bee
Ridge Road to six-lane Fruitville Road through two-lane Cattlemen Road. During PM peak
hours, Bee Ridge Road, Cattlemen Road and eastbound of the Fruitville Road are congested.
The simulation results indicate that optimal signal coordination with I-75 diverted traffic only
(Scenario 6) to the alternative route is slightly better than self-diversion (Scenario 2) for a 100-

min incident duration. No benefits will be obtained to divert traffic to the alternative route when
the incident duration is 80 minutes or less. If 80% of I-75 northbound destined traffic from Bee
Ridge Road also uses the alternative route, the average delay per vehicle will be larger than that
of Incident Base scenario. As expected, signal coordination is the best among all signals timing
strategies. With ATIS only, the green time for westbound is not adequate at the Bee Ridge and
Cattlemen intersection to serve northbound I-75 diverted traffic to make a right turn from Bee
Ridge Road to Cattlemen Road. The queue backs up from this intersection quickly causing the
queue to back up on I-75 southbound ramp at Exit 38. Eventually, it causes I-75 southbound to
shut down. The advantages of this alternative route include long westbound right-turn lane at the
Bee Ridge and Cattlemen intersection, close distance to I-75, six-lane Fruitville road, and higher
speed limits on the alternative route. This alternative route also comprises several drawbacks.
More signalized intersections exist on the alternative route due to the types of freeway
interchanges. In addition, the major turning point of the alternative route at the congested Bee
Ridge and Cattlemen intersection is only 750 feet from the Bee Ridge/I-75 West Ramp
intersection, which may easily cause I-75 to back up during PM peak hours with heavy diverted
traffic. Moreover, Bee Ridge Road has a 4-lane section approximately 1000 feet west of the Bee
Ridge and Cattlemen intersection. During PM peak hours, any I-75 traffic diversion will have
significant impact to eastbound traffic on the Bee Ridge Road.
Case 4. Incident on southbound of I-75 between Exit 38 and Exit 39: Signal timing strategies
and southbound alternative route from Exit 39 to Exit 38 are evaluated in this case. Simulation
results identify self-diversion (Scenario 2) to alternative route is the best plan base on the
average delay per vehicle in the network. The diversions of heavy traffic to a congested
alternative route only make the situation worse. More traffic is diverted to the alternative route,
causing more total delay and total travel time to be generated. During PM peak hours, self-
diversion is encouraged for any incident duration. The largest average delay occurs if motorists
are diverted to the alternative route without any signal timing adjustment. With ATIS only,
northbound traffic on I-75 is blocked from northbound off ramp at Exit 39 due to westbound
queue on the Fruitville Road. This alternative route has advantages of dual right-turn lane at
southbound off ramp at Exit 39, dual southbound lane at the Cattlemen and Bee Ridge
intersection, fewer traffic signals along the alternative route, close distance to I-75, six-lane
Fruitville road and higher speed limits on the alternative route. The major drawbacks include a
short westbound left-turn lane at the Fruitville and Cattlemen intersection, and short distance
between this major turning point of the alternative route and Fruitville and I-75 West Ramp
intersection. The main reason for very limited benefits on this alternative route is because the
diverted traffic has to travel against heavy eastbound traffic on both Fruitville Road and Bee
Ridge Road during PM peak hours. This case will benefit from the alternative route if a
southbound I-75 incident occurs during off peak hours.
Case 5. Incident on northbound of I-75 between Exit 37 and Exit 38: This case examines
signal timing strategies on the northbound alternative route from Clark Road to Bee Ridge Road
through Honore Avenue when a northbound I-75 incident happens between Exit 37 and Exit 38.
Honore Avenue is used as an established alternative route. Some local motorists may use Gantt
Road, Proctor Road and Cattlemen Road as an alternative route instead of using Honore Avenue.
This type of diversion is also included in the case study. The simulation results reveal no
significant difference between different signal timing strategies, and no significant difference
between different traffic volume diverted. The positive side of this alternative route include

more capacity on Honore Avenue because of light traffic volume and better signal coordination
on Bee Ridge Road from Honore Avenue to I-75. Another advantage is that local motorists may
use Gantt Road, Proctor Road and Cattlemen Road as another alternative route, so the diverted
traffic will be more evenly distributed. Additionally, six-lane Clark Road carrying moderate
traffic volume provides sufficient capacity for diverted traffic. The major disadvantage of this
alternative route is the distance of the diverted route is relatively long compared to the distance
on I-75 between Exit 37 and Exit 38. In addition, Honore Avenue is only a two-lane minor
artery and Bee Ridge Road has a long section with four lanes serving generally heavy traffic
volume on this alternative route.
Case 6. Incident on southbound of I-75 between Exit 37 and Exit 38: This case explores the
signal timing strategies on the southbound alternative route from Exit 38 to Exit 37. This
alternative route starts from westbound Bee Ridge Road at I-75 southbound off ramp to
eastbound Clark Road at I-75 southbound on ramp through southbound Honore Avenue. Clark
road is a six-lane highway with a speed limit of 45 mph. There is plenty roadway and
intersection capacity available on Clark Road. Therefore, this case can be used to exemplify the
diversion of traffic from the congested area to the area with sufficient roadway capacity. As
expected, the simulation result shows that given incident related information, diversion of traffic
to the alternative route with any signal timing strategy is much better than only self-diversion
without information in the Incident Base scenario. The scenario with traffic diversion from both
I-75 and Bee Ridge Road to the alternative route associated with optimal signal coordination
timing plan provide the most benefits to motorists in the network. The reductions of average
delay per vehicle are 5%, 15%, 22% and 25% for incident duration of 40, 60, 80 and 100
minutes, respectively. If only I-75 traffic is diverted, the average delay per vehicle significantly
increases. This case demonstrates that more traffic diversion can better utilize the available
capacity on the alternative route. More traffic diversion is encouraged when sufficient capacity
is available. The major advantage of this alternative route includes more capacity available and
fewer traffic signals on the alternative route. Cattlemen Road can also share some of diverted
traffic of local motorists. The disadvantage of this alternative route is the distance of the
diverted route is relatively long when it is compared to the distance on I-75 between Exit 37 and
Exit 38. The diverted traffic has to travel against heavy eastbound Bee Ridge traffic at the Bee
Ridge and Honore intersection.
CONCLUSIONS AND RECOMMENDATIONS
Several valuable lessons have been learned in this research through case studies evaluating
signal timing strategies on establish alternative routes in response to freeway incidents in small
urban areas. From the results of the study, many conclusions can be made and recommendations
can be given. They are listed as follows.
1. The average delay per vehicle in the network increases dramatically when the incident
duration increases. This study shows the average delay per vehicle increases 23%, 93% and
204% for incident duration of 20, 60 and 100 minutes respectively. The total travel time in
the network increases 3%, 22% and 51% for incident duration of 20, 60 and 100 minutes
respectively.

2. With the support of ATIS and ATMS, adequate signal timing plans on established alternative
routes in response to a freeway incident can significantly reduce total delay and travel time of
motorists if plenty of roadway capacity is available on alternative routes. The best network
performance in terms of measure of effectiveness (MOE) is dependent on the balance of
traffic distribution in the roadway network. More diverted traffic can be encouraged when
there is sufficient capacity on the alternative route. No informed diverted traffic is
recommend if the alternative route is heavily congested. The key to achieve proper amount
of diverted traffic is to provide adequate information to motorists through ATIS.
3. If only incident and alternative route information is provided to motorists near the incident
location without signal timing adjustment on the established alternative route (with ATIS
only), total delays in the affected roadway network will generally significantly increase.
With ATIS only, diverted traffic may easily cause heavy traffic congestion on local arteries
and the other direction of freeway without an incident through lane blockage.
4. In a freeway incident, informed traffic diversion from both affected freeway and local artery
to an alternative route is not always better than self-diversion even with optimum signal
timing plans in response to the incident. When the local arteries become more congested,
traffic diversion to alternative routes shall be limited to some traffic from freeway or local
artery. When local arteries are congested and the major signalized intersection at the turning
point of the alternative route is very close to the freeway, no informed traffic diversion from
the freeway is recommend.
5. When plenty of roadway capacity is available on the alternative route, the total delay in the
network will become less if more traffic is diverted. The full utilization of available capacity
on the alternative route can reduce the total delay in the network.
6. For traffic management on the alternative route, the strategy of signal coordination is
generally better than free operation and no signal timing change. In some cases, the optimal
free operation can be as effective as optimal signal coordination on the alternative route.
7. More signalized intersections on the alternative route will increase the total network delay.
In this study, all southbound alternative routes have fewer signalized intersections than their
respective northbound alternative routes. The southbound alternative routes are all on the
west side of the freeway. The northbound alternative routes are in the east side of the freeway
to get in and out, while the rest of northbound alternative routes are the west side of the
freeway. Under this condition, the diversion of freeway and local traffic to alternative route
due to a northbound freeway incident in Sarasota urban area become less beneficial. During
the typical PM peak hours in Sarasota urban area, only one of three informed traffic
diversions to alternative routes due to a northbound I-75 incident can gain some benefit.
However, for southbound incidents on I-75, two of three established alternative routes with
optimal signal coordination can gain significant reduction in both vehicle delays and total
travel time.

8. There is no significant reduction on delay and travel time by operating alternative routes with
optimal signal timing when the incident duration is less than 30 minutes.
9. The maximum green times allowed for the movements at both signalized intersections at
freeway ramps to divert freeway traffic to an alternative route shall not be too long, which
can cause the other direction of freeway to back up
10. The conclusion from one case study can not directly apply to the other one because the types
of freeway interchange, traffic conditions on affected network and characteristics of the
alternative route vary from one case to the other. It is recommend to follow the general
guideline in the literature to establish an alternative route, develop special signal timing plans
in response to estimated diverted traffic from a freeway incident, and then verify the
operation plan with microscopic traffic simulation.
11. Analytical model has its limitation to evaluate the operation of alternative routes due to a
freeway incident. Microscopic traffic simulation is an excellent tool to verify the final signal
timing plan on the established alternative route and identify potential problem areas during
traffic diversion. ATMS can be used to effectively monitor traffic flow especially at
potential problem areas during actual traffic diversion. Proper use of ATIS to inform
motorists may achieve optimal amount of diverted traffic to alternative route and make the
most use of available roadway capacity.
12. Diversion of affected traffic to alternative routes due to a freeway incident shall not be
limited to the traffic on the freeway. When the alternative route is congested and the
diversion of freeway traffic cannot gain real benefits, proper diversion of traffic on local
arteries through ATIS may reduce the total delay and travel time of motorists. It may
effectively reduce the burden of overloaded freeway and fully utilize the available capacity
on established alternative routes. The evaluation on the informed diversion of local traffic
through ATIS associated with self-diversion of freeway traffic in response to a freeway
incident will be conducted in further studies.
ACKNOWLEDGEMENTS
The author would like to express his gratitude to Mr. Don Galloway, Mr. Ted Hoffman and Mr.
Gene Riggs for their full support and professional guidance for this study. He would also like to
thank Mr. Phuoc Hoang, Mr. Sage Kamiya, Mr. Thai Tran and Mr. Chad Rorstrom for their
encouragements and assistances. Finally, he would like to express his deep appreciation to his
wife, Hui-Min Wen for her continuous support and inspiration.
REFERENCES
Abdel-Rahim, A. (2001) – “Assessment of potential Delay Reduction Benefits of Freeway
Diversion Routes plans in Integrated Incident Management Systems” – National Institute
for Advanced transportation Technology, University of Idaho, Moscow, USA.

Brist, S., Smadi, A. (1999) – “An Application of ITS for Incident Management in Second-Tier
Cities” – Upper Great Plains Transportation Institute, North Dakota State University,
Fargo, USA.
Cuneo, D., Jha, M., Ben-Akiva, M. (1999) – “An Evaluation of Integrated Freeway Traffic
Control and Route Diversion using Microscopic Simulation”- Intelligent Transportation
Systems Program, Massachusetts Institute of Technology, Cambridge, USA.
Federal Highway Administration (2000) – “Traffic Incident Management Handbook” –
Department of Transportation, USA.
Johnson, C. (2001) – “Operations Dialogue: A Report on the Progress” – Institute of
Transportation Engineers, Spring Conference, March 25, 2001, Monterey, USA.
Pearce, V., Subramaniam, S. (1998) – “Intelligent Transportation Systems Field Operational Test
Cross-Cutting Study Incident Management: Detection, Verification, and Traffic
Management.” – Report FHWA-RD-JPO-034 – U.S. Department of Transportation,
Washington, D.C., USA.
Presley, M.W., Wyrosdick, K.G. (1998) – “Calculating Benefits for NAVIGATOR, Georgia’s
Intelligent Transportation System” - Georgia Department of Transportation, USA.
Skabardonis, A., Petty, K., Varaiya, P., Bertini, R. (1998) – “Evaluation of the Freeway
Service Patrol (FSP) in Los Angeles” – Report Number UCB-ITS-PRR-98-31 –Los
Angeles, USA.
Tavana, H., Mahmassani, H.S., Haas, C.C. (1999) – “Effectiveness of Wireless Phones in
Incident” – University of Texas at Austin, Austin, USA.
Trueblood, M. (2001) – “Should I Use CORSIM or SimTraffic?” – HDR Engineering, Omaha,
USA
Walters, C.H., Wiles, P.B., Cooner, S.A. (1999) – “Incident detection Primarily by Cellular
Phones--An Evaluation of a System for Dallas, Texas” - Transportation Research Board,
Washington, D.C., USA.
Wei, W. (1998) – “Variable Message Signs” – ITS Decision.
<http://www.path.berkeley.edu/%7Eleap/travelerinfo/Driver_Info/message.html>.
Author’s Information:
Pei-Sung Lin, Ph.D., P.E.
Traffic Engineer
Sarasota County Public Works
Sarasota, FL
Tel: 941-861-0813 Fax: 941-861-0542
Email: plin@co.sarasota.fl.us
Dr. Lin is an associate member of ITE, member of ITE Transportation Management Center
Committee, member of ITS Florida, and member of Florida Statewide Incident Management
Program Committee.