Long Range Deployment of ITS Strategies:
Concept Definition
A considerable amount of effort in the past has been
devoted to developing methodologies for short-range ITS deployment. This
report deals with the issue of how ITS (Intelligent Transportation Systems)
strategies and technologies should be implemented over a long period of time
(e.g., 10 to 20 years).
This report addresses the following questions:
- Are there many ITS strategies that have long-range
implications and, if so, which of the strategies have greatest relevance?
- Is there a consensus as to the best way of performing
strategic ITS deployment planning? What features of strategic ITS planning
should be retained for long-range ITS planning?
- What is the status of software tools for investigating
the effects of ITS deployment over the long range? Can existing software
tools be successfully used in long-range ITS deployment planning? How can
those software tools be improved to provide better evaluations of ITS
deployment plans? What are the obstacles?
- Can a workable methodology for long-range ITS
deployment planning be demonstrated?
- What conclusions can be reached about long-range ITS
deployment planning?
Are there many ITS strategies that have long-range
implications and, if so, which of the strategies have greatest relevance?
A review of all ITS strategies in the National ITS
Architecture CD-ROM found twelve important strategies that had long-range
implications. Of these twelve strategies only a few are of particular
relevance to transportation engineers in the Midwest region. The following
three items provide a more focused set of strategies.
A.
Integration of the network signal systems control with the controls of
freeways. This item would also include elements of the control of traffic
signalization, principally area wide.
B.
Management of scheduled/planned incidents (including traffic spikes
from special events).
C.
Pre-trip and en route information to assist travelers in making mode
choices, travel time estimates and route decisions prior to departure. This
item would also include control of dynamic traffic signing (including the
signs) and en route driver information that facilitates the choice of
alternative routes.
These particular strategies served as reference points
for the evaluation and formulation of tools for long-range ITS deployment
assessment in the rest of the report.
Is there a consensus as to the best way of
performing strategic ITS deployment planning? What features of strategic ITS
planning should be retained for long-range ITS planning?
A review of many strategic ITS plans revealed that a
complete planning effort should involve the following elements.
·
Identify User Needs
·
Establish Goals
·
Recognize Conventional Approaches
·
Establish Objectives
·
Identify Candidate ITS Strategies
·
Conduct a Selection Process
·
Elicit Stakeholder Input
·
Prepare Deployment Plan Including Alternatives
·
Measure Criteria by MOEs (Measures of Effectiveness) and Other
Assessment Means
Long-range ITS
deployment planning should contain the same elements as strategic ITS
deployment planning, but it must also recognize the peculiarities of
forecasting traffic conditions many years into the future.
Scenarios and
Alternatives. In order to correctly identify staging, long-range ITS
planning involves a time stream of scenarios, each one is a consequence of its
immediately prior scenario. An ITS alternative make sense only within the
context of a scenario.
Staging. A
complex staging process may be required for good long-range ITS plans. This
complex staging recognizes that (1) earlier years have ITS and conventional
infrastructure that is worth preserving and (2) travel patterns may have been
altered because of alternatives selected in an earlier year. Such a complex
staging process would be difficult to accomplish manually and would be greatly
facilitated with specialized software that optimizes the deployment in any
given year. A simple example of a variable message sign deployment
illustrates how complicated the staging process can become.
Optimization Multiple Criteria and Grandfathering.
Almost all long-range transportation plans are based on multiple criteria,
such as travel time savings, safety, air pollution emissions, capital costs
and maintenance costs. The method by which multiple decision criteria within
an optimization framework is handled is critical to the results.
Grandfathering is a form of a constraint on the optimization by specifying
that certain ITS elements must be selected in a given year.
Stakeholder Input. Stakeholder input assures
that the alternative is technically feasible, but getting adequate stakeholder
input during an automated choice process would be very difficult. Stakeholder
input can occur only at the beginning (proactive) or end (reactive) of the
process. Essential proactive stakeholder input includes:
- Cost data on deployment alternatives, both fixed and
variable, and projections as to how costs may decline with time;
- The degree to which grandfathering needs to be
respected;
- Estimated availability dates on technologies;
- The life span of candidate technologies and equipment
and depreciation rates;
- Constraints on deployment;
- Logical arrangements of elements;
- Synergies between various elements;
- Performance characteristics of elements; and
- Opinions as to the best way to represent the
performance of an element in software.
Recognition of Random Situations. A strength of
ITS is the ability to respond to unusual events, often random. The standard
method of benefit-cost analysis to dealing with random situations is to find
the “expected benefit” by weighting the benefits of a deployment with a random
situation by the probability of that situation occurring. Similar reasoning
applies to costs of random situations.
Costs and Technologies. It is well known that
the costs of communication and information technologies decline with time, so
it is may be necessary to make costs of deployment a function of time, which
can improve the cost effectiveness of certain ITS options in the later years
of the plan.
What is the status of software tools for
investigating the effects of ITS deployment over the long range? Can existing
software tools be successfully used in long-range ITS deployment planning?
How can those software tools be improved to provide better evaluations of ITS
deployment plans? What are the obstacles?
There are eight classes of simulation software packages
that can help evaluate long-range ITS deployment plans. They are:
- Traffic Microsimulation
- Mesoscopic Traffic Simulation with Dynamic Traffic
Assignment
- Macroscopic Traffic Simulation
- Traditional Four-Step Travel Forecasting with Static
Traffic Assignment
- Travel Demand Microsimulation
- Hybrid of Four-Step with Traffic Microsimulation
- Four-Step with Integrated Macroscopic Traffic
Simulation
- Specialized Static Traffic Assignment for ITS
Evaluation
A comparison of the general characteristics of these
classes of tools indicated that four classes had the greatest potential for
simulating long-range ITS strategies. A single software package representing
each of these four classes was reviewed for meeting the needs of the problem.
They were IDAS (specialized static traffic assignment for its evaluation), QRS
II (four-step with integrated macroscopic traffic simulation), Paramics
(traffic microsimulation), and Dynasmart-P (mesoscopic traffic simulation with
dynamic traffic assignment). Each of these packages has its separate
strengths and weakness and none is currently suitable for long-range ITS
deployment. All of the packages share several weaknesses:
·
Staging. None of the software packages is able to
simulate a sequence of deployments, where the decisions in some distant future
year are dependent upon outcomes in an earlier future year.
·
Realism of Traffic Simulation across a Wide Spectrum of ITS
Strategies. No software package exists that can correctly simulate
(according to accepted traffic flow theory or theory of travel behavior) a
wide spectrum of ITS strategies.
·
Alternative Selection. None of the software packages is
able to choose an optimal combination of ITS elements (or even a reasonably
good combination).
·
Adaptiveness. The software packages, for the most part,
are not adaptive beyond allowing for actuated signals. That is, the software
packages cannot make many of the routine and rationale judgments that a
traffic engineer would make.
·
Optimization of Traffic Operation.: None of the software
packages optimize the operation of existing facilities or traffic controls
within those facilities.
·
Random Effects. None of the models, with the possible
exception of single, isolated incidents in Paramics, adequately addresses
random effects.
Many of the weaknesses in individual packages may be
overcome by combining the best parts of several software packages. The
resulting package might be referred to as a dynamic travel forecasting model (DTFM).
An experimental DTFM was constructed for this project by modifying the source
code of QRS II to include essential algorithms of Dyasmart-P. A few lessons
were learned from building the DTFM. (a) No serious compromises need be made
to combine the methodologies. (b) Computation times are greatly increased
over a traditional travel forecast, but computer hardware requirements are
essentially the same. (c) Since a DTFM creates its own origin-destination
tables, this difficult input requirement of a dynamic traffic assignment is
eliminated. The DTFM can be embedded within an optimizing framework.
Can a workable methodology for long-range ITS
deployment planning be demonstrated?
Two different approaches are demonstrated for modeling
the long-range deployment of ITS strategies: (1) the use of a DTFM embedded
within an optimizing computer program in order to choose the locations for
freeway incident management; and (2) the use of an existing computer program (IDAS)
to find a reasonable sequence of ITS deployments.
An optimal long-range freeway incident management plan
was automatically created for the smallish Utown test network by repeatedly
running the DTFM. Among the 124 links in this network, 12 links constituted
almost the entire mainline freeway. After accounting for stakeholder input,
it was possible to reduce the number of possible alternatives to 21, including
the null alternative. Each alternative consisted of a set of contiguous
freeway segments to receive incident management. In each of four planning
years, separated by five calendar years each, all 21 alternatives were
evaluated to determine whether user benefits exceed the costs of operating the
incident management program. In order to evaluate the benefits of incident
management it was necessary to individually simulate the effects of a large
number of incidents (both managed and unmanaged) and consider the probability
that any one of the incidents would occur. Traffic volumes were assumed to
grow through time. The optimization/simulation demonstrated the technical
feasibility of using a DTFM to evaluate ITS deployments and the advantages of
incorporating stakeholder input into the process at the earliest stages of the
planning process. The optimization/simulation also demonstrated how growth in
traffic can affect the design of ITS strategies and affect user benefits
associated with any given strategy.
In a separate set of simulations, a long range ITS
deployment plan was created for the full-sized Cedar Rapids network using IDAS,
an existing computer program developed for the Federal Highway
Administration. IDAS does not automatically design ITS strategies, so it was
necessary to develop all possible strategies using engineering judgment before
letting IDAS choose the best strategy in any given planning year. IDAS cannot
automatically consider combinations of strategies, so each strategy was
separately evaluated in each planning year. As strategies were selected, they
were grandfathered into all future year plans. Thus, strategies accumulated
over time. Using IDAS in this way produced a plausible deployment plan, but
it is difficult to tell if the plan is even close to being optimal.
What conclusions can be reached about long-range
ITS deployment planning?
These following points are a brief summary of the major
conclusions of this study.
·
There are many ITS strategies that have long-range deployment
issues.
·
Long-range ITS deployment planning can be conducted using
essentially the same process as strategic ITS planning, except that staging
decisions become more explicit, stakeholder input is needed at different
points in the process and different methods are needed to forecast the effects
of ITS elements on future traffic conditions.
·
Primary difficulties in generating and evaluating ITS
alternatives relate to the huge number of possible alternatives and the needs
to consider prior year commitments, short-lived traffic phenomenon and random
effects.
·
Currently there is no software package that can adequately
evaluate long-range ITS deployments.
·
When using simulations to evaluate ITS alternatives, it is
essential that stakeholder input be solicited prior to specifying the
simulation.
·
The generation of alternatives is a combinatorial optimization
problem where there can be a very large number of possible alternatives.
Stakeholder input is critically important as it may have a constraining effect
on the number of solutions, making the optimization more tractable.
- It is recommended that both an IDAS-like model and a
DTFM be used to evaluate long-range ITS deployment strategies. An IDAS-like
can be used to incorporate stakeholder input into a screening process for
workable alternatives. The DTFM can be used to refine and optimize those
alternatives selected by the IDAS-like model.
This report deals with the issue of how ITS
(Intelligent Transportation Systems) strategies and technologies should be
implemented over a long period of time (e.g., 10 to 20 years). It is common
practice for long-range transportation plans to include ITS elements, but
there is not a coherent body of methodologies for deciding when and how ITS
strategies should be deployed in accordance with asset management or
transportation planning principles.
There are four principal complicating factors when
attempting to determine the timing of ITS strategies. First, the
effectiveness of many ITS strategies (e.g., ramp metering and incident
management) depend on the level of traffic demand. As traffic demand grows
and shifts to new locations, ITS strategies that would have previously been
ineffective may become effective or vice versa. Second, ITS technologies
require a considerable amount of maintenance and other operational resources
and are subject to obsolescence and depreciation. Thus, a premature
deployment of an ITS technology could result in substantial unwarranted
costs. Third, there is often a logical order to ITS strategies; some
strategies should precede others. Fourth, many ITS strategies affect traffic
demand, either by design or by unintended consequence and those changes in
demand may affect future deployment decisions. The complexity, scope, and
geographic range of certain strategies should grow according to a rational
process through time.
A considerable amount of effort has already been
devoted to developing methodologies for short-range ITS deployment. For
example, the federal government has recently developed IDAS (ITS Deployment
Analysis System), a computer program for evaluating individual and
combinations of ITS strategies. Also, there are many computer programs for
determining optimal ramp meter arrangements and for optimizing other specific
ITS elements. However, there has not been a significant body of research that
addresses the long-range ITS deployment problem.
This report addresses the following questions:
- Are there many ITS strategies that have long-range
implications and, if so, which of the strategies have greatest relevance?
- What is the status of software tools for investigating
the effects of ITS deployment over the long range? Can existing software
tools be successfully used in long-range ITS deployment planning? How can
those software tools be improved to provide better evaluations of ITS
deployment plans? What are the obstacles?
- Is there a consensus as to the best way of performing
strategic ITS deployment planning? What features of strategic ITS planning
should be retained for long-range ITS planning?
- Can a workable methodology for long-range ITS
deployment planning be demonstrated?
An ITS deployment consists of one or more strategies,
each consisting of one or more elements. An element is most often a single
implementation of a device, such as a variable message sign, a ramp meter or a
pre-emptive signal. A strategy is typically a package of like elements that
help accomplish a goal for the transportation system. The next section
contains a list of strategies that are particularly interesting from a
long-range deployment perspective.
Eventually, this report will describe methods of
accomplishing long-range deployment of ITS strategies, both procedural and
analytical. Some of the methods are complicated and abstract, so it is
helpful to first define the types of strategies that are subject to these
methods and to then use those strategies as reference points and case
studies. Given the large number of possible strategies, there is a further
need to focus on a few of them that have the greatest long-range implications
for the Midwest region of the United States.
The following list of strategies illustrates the need
for a long-range perspective when developing ITS deployment plans. These
strategies were culled from the National ITS Architecture and are described in
terms of seven attributes: the type of urban environment where the strategy
could be deployed; the readiness of the technology; the amount of current
deployments; prerequisites for implementation; reasons why the strategy has
long-range implications; and whether traffic operations models or travel
forecasting models can be used for the strategy’s evaluation. These
attributes were assessed partially by reference to the document “What Have We
Learned about Intelligent Transportation Systems?” (FHWA, 2000).
1. Integration of the network signal systems control
with the controls of freeways
- Applies to any city with freeways
- Not off-the-shelf technology
- Few current deployments
- Prerequisites: would need a seriously restrictive
freeway control strategy, such as ramp meters or ramp gates; needs standards
for interoperability
- Long-range because: (a) future technology; (b)
benefits depend on levels of congestion
- Can be partially assessed with a traffic operations
model (without traffic rerouting)
- Very complex to assess through a travel forecasting
model
2. Preferential treatment for transit vehicles,
including diamond lanes and preemptive signalization
- Applies to any city with bus transit, on-street
light-rail transit
- Off-the-shelf technology
- Limited deployments
- Prerequisites: none
- Long-range because: (a) benefits depend on level of
congestion; (b) precision of existing signal timing; (b) emissions by
competing modes
- Can be partially assessed with a traffic operations
model (without mode split or traffic rerouting)
- Not difficult to assess with a travel forecasting
model
3. Preferential treatment for HOV (high occupancy
vehicles) (other than transit)
- Applies to any city with wide freeways and ramp meters
- Conventional technology
- Widespread deployment
- Prerequisites: none
- Long-range because: (a) benefits depend upon number
of lanes and automobile occupancy; (b) emissions by competing modes
- Can be partially assessed with a traffic operations
model (without mode split or traffic rerouting)
- Not difficult with a travel forecasting model
4. Control of traffic signalization, principally
area-wide
- Applies to any city
- Off-the-shelf technology
- Limited deployment
- Prerequisites: needs extensive communications
hardware
- Long-range because: (a) benefits depend upon network
complexity and signal density; (b) benefits depend upon the level of
congestion; (c) deployment depends upon less intense strategies having been
implemented first
- Can be partially assessed with a traffic operations
model (without traffic rerouting)
- Can be analyzed with a travel forecasting model,
provided some good signal delay routines are included in the software
5. Control of dynamic traffic signing (including the
signs)
- Applies to any city, but probably most applicable to
one with freeway congestion
- Off-the-self components
- Moderate level of deployment
- Prerequisites: needs communications hardware, VMSs
- Long range because: benefits depend on having
considerable congestion or relatively frequent occurrences of LOS F
traffic
- Cannot be assessed with a traffic operations model, as
benefits relate to the ability to reroute traffic
- Can be analyzed with a travel forecasting model with
assumptions about the degree of rerouting that can occur during typical
situations
6. Dynamic control over the infrastructure (reversible
lanes, turning restrictions, etc.)
- Applies to any city
- Some off-the-shelf components
- Limited deployment
- Prerequisites: needs extensive communications
hardware
- Long-range because: (a) deployment depends upon less
intense strategies having been implemented first; (b) driver acceptance may
take time to develop
- May be difficult to assess with a traffic operations
model, depending upon the type of sign and the accuracy of behavioral
assumptions
- Difficult for a travel forecasting model to show
sensitivity to some types of signs
7. Management of scheduled/planned incidents
- Applies to any city, but more so to cities with
congested freeways
- Conventional technologies
- Moderate level of deployment
- Prerequisites: none
- Long-range because: benefits depend upon the level of
congestion
- Cannot be analyzed with a traffic operations model
because of the need to handle traffic rerouting, mode split and time-of-day
issues
- Can be analyzed with a travel forecasting model, but
some assumptions about the reaction of drivers would be necessary
8. Coordinated response to incidents
- Applies to any city, but more so to cities with
congested freeways
- Off-the-shelf technologies
- Moderate level of deployment
- Prerequisites: must have considerable infrastructure
of VMSs and other communication technologies and (perhaps) means to control
entry to freeways
Long
Range
Deployment of ITS Strategies: Concept Definition