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Publication Number: FHWA-HRT-13-036
Date: August 2013

 

The Effective Integration of Analysis, Modeling, and Simulation Tools

MULTI-RESOLUTION AMS TOOL INTEGRATION

INTRODUCTION

Existing AMS tools have the capability to meet the needs of specific and relatively simplistic activities performed by different agencies. However, these tools have limited capacity to replicate complex system performance across different domains. For example, macroscopic TDMs are incapable of modeling detailed signal control, making them unsuitable to model traffic management and control alternatives. Running speed is a constraint for large networks in a microscopic simulation model. Real-time information and simulation of nonrecurring events are only available in the DTA and simulation models. Table 2 provides a high-level overview of AMS capabilities.

Table 2. Capabilities of AMS tools.


Domains

Capable of Replicating the System Performance

Running Speed

Receive Real-Time Information and Simulate Nonrecurring Events

Macroscopic TDMs

Yes on planning level network

Reasonable running speed for large network

No

Mesoscopic DTA models

Yes on subarea network level

Longer than macroscopic TDM

Yes

Microscopic simulation models

Yes on small network

Requires significant running time for large networks

Yes

Activity-based models

Possible, calibration is resource intensive

Slow to medium

No

Static deterministic programs

Yes on nodes and link level

Fast

No

Safety

Still developing

Fast

No

Land use models

Possible, calibration is resource intensive

Slow to medium

No; typically modeled for 5 years

Emissions

Yes

Fast

No

Although it is not suggested to use a single model across purposes for different domains, transportation models can be integrated on many levels because most of these domains are correlated with others on multiple dimensions. Figure 3 illustrates possible integration links between multiple AMS domains in transportation. The user may need to perform an integrated process when a comprehensive and complex transportation analysis is needed. The software tools for most of the integration links between the model domains in figure 3 are either unavailable, still in the research/development phase, or can be purchased as proprietary software programs. In many cases, users need to manually edit or create their own utility tools for integration purposes.

This figure  provides a complex, multi-dimensional illustration of possible integration links between multiple analysis, modeling, and simulation (AMS) domains in transportation. The elements of the illustration are set against an x-y axis. The y-axis represents degree of aggregation and runs from individual/segment at the lower end of the axis through transportation analysis zone (TAZ) and urban areas at the upper end of the scale. The x-axis represents domain and runs from land use at the far left through travel demand, traffic operations, and pollutant/safety at the right end. Activity-based models (DASHTM and DaySIMTM), located at the lower left of the diagram near the intersection of the x-axis and the y-axes correspond to the land use domain and the individual/segment degree of aggregation. Mesoscopic dynamic traffic assignment (DTA) models (DynaSmart-PTM and Dynus-T) correspond to the travel demand domain and the individual/segment degree of aggregation. Both of these model types are labeled “TRANSIMS,” and a double headed arrow connects the two. Single-headed outbound arrows also link mesoscopic DTA models to microscopic simulation models, deterministic operation models, and the emissions models elements. Land use models (PECAS tool and UrbanSim) correspond to the land use domain and the TAZ degree of aggregation. This model type connects with a double-headed arrow to the macroscopic travel demand models (TransCADTM, Cube/TP+®, and PTV Visum®), which corresponds to the travel demand domain and the individual/segment degree of aggregation. Double-headed arrows connect the macroscopic travel demand models to the mesoscopic DTA models, and single-headed outbound arrows connect the macroscopic travel demand models to safety models, emissions models, deterministic operation models, and microscopic simulation models. Sketch planning tools straddle the travel demand and travel operations domains and correspond to the urban area degree of aggregation. This element is standalone and has no link to other elements. The safety models (PLANSAFE) correspond to the traffic operations domain and straddles the TAZ and urban area degree of aggregation. A single connector leads from the macroscopic travel demand models element to the safety models element. The microscopic simulation models (PTV Visum®, Paramics®, CORSIMTM, and Transmodeler®) correspond to the transportation operations domain and the individual/segment degree of aggregation. Connectors lead from this model type to the emissions models and deterministic operation models. Connectors also lead back to this element from mesoscopic DTA models and macroscopic travel demand models. The emission models (MOVES) correspond to the pollutant/safety domain and the TAZ degree of aggregation. Single connectors lead from the microscopic simulation models, the mesoscopic models, and the macroscopic travel demand models to the emissions models. Finally, deterministic operation models (HCSTM, Synchro®, PASSERTM, and TRANSYT-7FTM) correspond to the pollutant/safety domain and the individual/segment degree of aggregation. Single connectors lead from the microscopic simulation models, the mesoscopic DTA models, and the macroscopic travel demand models elements to the deterministic operation models element.
Figure3. Illustration. Level of aggregation for various AMS tool domains.

USE CASES

Several existing example use cases pertain to supporting transportation decisionmaking to solve complex challenges facing the transportation system. These challenges are multi-modal and diverse by geographic location. Temporal elements have multiple interrelated influences on the system including traffic demand, transportation capacity/supply, economic market forces, land use allocations and decisions, environmental conditions, and the desire to reduce crash frequency, to name a few. Table 3 presents a summary list of example use cases, typical user agency(s) that may be involved, current practice, and improved practice. The improved practice should be driven by the development and use of the AMS data hub.

Table 3. Use cases for AMS tool integrated modeling applications.


Use Case

Typical User Agency

Current Practice

Improved Practice

Long-term planning

Metropolitan planning organization (MPO)

TDM with static assignment

Integrate with DTA, emissions, safety, economic, land use models, and field data

Prioritization of projects

MPO, transportation department, local agencies, and transit

TDM

TDM to DTA models, feedback to land use, activity-based, emissions, and safety models

Corridor planning

Transportation department, transit, and local agencies

TDM, HCM, and sometimes microsimulation

TDM to DTA to HCM models and/or micro-simulation, emissions, safety models, and field data

Construction sequencing and detour impact

Transportation department

Limited analysis or microsimulation

DTA to microsimulation field data, predictive scenario planning, and active traffic management

Congestion hotspot

MPO and transportation department

TDM or field observation

DTA to microsimulation and field data

Traffic impact study

Transportation department, local agencies, and property owner

TDM to HCM

TDM to DTA to HCM and safety, land use, and economic modeling

Intelligent transportation system (ITS) evaluation and operations planning

Transportation department and MPO

ITS Deployment Analysis SystemTM

DTA to microsimulation, field data, predictive scenario planning, and active traffic management

Safety evaluation and planning

Transportation department

Sketch planning or field observation (safety audit)

Integrate with DTA, microsimulation, and empirical crash data

Transit network improvement

Transit agency and MPO

TDM

DTA or microsimulation, feedback to activity-based models, land use, emissions, empirical operations data, etc.

Land use planning

MPO and local agencies

Land use model

Integrate land use models with transportation models
to reflect real relationship, integrate with economic,
and emissions modeling

Emissions

MPO

TDM to motor vehicle emissions simulator (MOVESTM)

DTA or microsimulation to MOVESTM; integrate with land use and economic models

Travel model update

MPO

Household travel survey, ad hoc integration of validation data from Census, traffic counts, and transit counts

Direct integration of estimation and validation data

NEEDED CAPABILITIES FOR EFFECTIVE MODEL INTEGRATION

A review of AMS tools and modeling practices has shown that current integrated modeling practices in transportation are mostly ad hoc and relatively inefficient. Inherent challenges to the modeling process include data constraints and inefficiencies, interoperability, calibration/validation, and adequate modeling behavioral response/feedback.

Data Constraints and Inefficiencies

Each stand-alone model program generally has sufficient data management techniques; however, each model program generally has a unique data format that impedes the ability to seamlessly integrate with other software programs. Effective model integration must bring diverse datasets into conformity. Currently, some users are developing ad hoc tools for integration. The lack of clear guidance and data standards is a barrier to entry for resource-constrained agencies that want to apply integrated modeling techniques. The following subsections provide additional detail regarding data constraints.

Data Availability

The types of input data required are often not readily available to modelers or are difficult to obtain, particularly for arterial streets and freeway off-ramps. A wave of new data sources, particularly probe-based data sources such as automatic vehicle identification, Bluetooth®, and data from private vendors along with real-time data from traffic signal controllers are becoming increasingly available for use in transportation modeling; however, these data sources are not yet widely integrated into standard modeling practices and still require significant labor resources to compile, postprocess, error check, and convert to a useful format.

Data Quality

Detector failure rates have been found to be as high as 60 percent, nearly double the 30 percent failure rate that is frequently cited as the average condition.(5) Poor data quality requires more time for scrubbing raw sensor data and raises questions about the credibility of modeling results.

Data Format

The lack of standardized data formats for common elements such as demand data (i.e., O-D, turning movement, vehicle trajectories, etc.), junction control data (i.e., signal timing), and, to a lesser extent, roadway network data requires manual manipulation or customization of utility tools to interface between models. This increases the risk of error in transposing data inputs. The additional effort also takes away from time that could be spent on calibrating/validating, running additional scenarios, and performing sensitivity tests.

Many AMS tools have proprietary components that are encumbered by copyrights or other restrictions. These limitations create impediments for exchanging data across independent software packages and require the development and application of individual utility tools.

Data Exchange

It is important to standardize data exchange between tools at different levels of resolution in order to fully integrate multiple stand-alone models or simulation programs. An open standard would enhance the interoperability of analytical/simulation tools to coordinate and work together in a common (virtual) environment. This ability requires the cross resolution model integration architecture to be built on a common understanding of the transportation network, traffic demand, traffic control devices, and traffic sensor data.

System Coupling

Although a full integration approach within a single platform is desirable for cross resolution modeling, it requires a common data model and single-user interface for geographic information system (GIS) and other data analysis software. Thus, it is more practical to develop a future integrated modeling approach using either a loose coupling approach or a tight coupling approach. The utility tools serving the transfer of data files between different resolutions of common models need to be well defined and designed in order to be scalable, modular, interoperable, and extendable. Individual models should be developed on a modular basis so that each module can perform its function and be easily connected and extended to meet future modeling needs.

Interoperability

Software developers are enhancing the functionality of their suites of programs to enable integrated and cross resolution modeling to act as a one-stop shop for modeling needs. Examples include PTV Visum/PTV Vissim® by PTV Group®, TransCAD®/TransModeler® by Caliper®, and Aimsun® by Transport Simulation Systems®. However, given the lack of industry-wide data standards and protocols, it is generally not feasible from a time and resource perspective for practitioners to work across multiple software-developer packages, and even if they did, the process would be far from seamless. This underscores the driving need to establish guidelines, standards, and protocols to address data handling and exchange.

CALIBRATION/VALIDATION

Few guidance or support tools exist for the calibration/validation of performance at a network level and for cross resolution model integration. Most validation is generally performed by qualitatively assessing the results and output for reasonableness. To the extent quantitative validation is performed, it is generally based on link or turning movement volumes. It is often difficult to validate performance measures such as travel time and route choice given the lack of available data, particularly when broken down for individual O-D pairs and routes.

The lack of calibration and validation can lead to a credibility issue with the public and decisionmakers and result in agencies shying away from applying data-driven models.

BEHAVIORAL RESPONSE

One of the most significant gaps in the functionality of current models is the lack of behavioral response associated with congestion, pricing, and traveler information (and other demand management strategies). Transportation models in many cases require significant manipulation and calibration to produce reasonable results for networks that are oversaturated and/or include demand management strategies that affect travelers’ choice of mode, departure time, and route. By only focusing on the supply side, many transportation analyses do not reflect the true effects of operating conditions, particularly when it comes to examining performance over multiple days for the purposes of estimating reliability. Ongoing research efforts are addressing this shortcoming and are expected to produce enhanced modeling tools and techniques that will establish a foundation for the future state-of-the-practice. As such, the development of standards, tools, and guidance as part of this project should look ahead to meet future modeling needs, not just current practice, which may soon be outdated in some cases.

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