Guide for Highway Capacity and Operations Analysis of Active Transportation and Demand Management Strategies
7 Use of Alternative Tools
There will be cases where finer temporal sensitivity to dynamic changes in the system will be required for the reliability analysis than can be provided by the typical 15-minute analysis period used by HCM methods. This may occur when evaluating and designing traffic-responsive signal timing, traffic adaptive control, dynamic ramp metering, dynamic congestion pricing, or strategies affecting the prevalence or duration of incidents with less than 10-minute durations. There may also be scenarios and configurations which the HCM cannot address, such as complex merging and diverging freeway sections.
The ATDM Analysis methodology can work with a wide variety of operations analysis tools ranging from microscopic simulation models, mesoscopic simulation models, traffic control optimization models, and Highway Capacity Manual (HCM)-based macroscopic analysis models. The key is to select an analysis tool with the appropriate geographic scale and sensitivities to ATDM improvements that meets the agency’s objectives for the analysis and at the same time has data and calibration requirements within the agency’s resource constraints.
For guidance on the selection of the appropriate analysis tool, the analyst should consult the following FHWA guidance documents:
- Volume I: Traffic Analysis Tools Primer;
- Volume II: Decision Support Methodology for Selecting Traffic Analysis; and
- Volume IX: Work Zone Modeling and Simulation – A Guide for Analysts.
The following documents at the same location provide additional guidance on the appropriate application of the various analysis tools:
- Volume III: Guidelines for Applying Traffic Microsimulation Modeling Software;
- Volume IV: Guidelines for Applying CORSIM Microsimulation Modeling;
- Volume V: Traffic Analysis Toolbox Case Studies – Benefits and Applications;
- Volume VI: Definition, Interpretation, and Calculation of Traffic Analysis Tools Measures of Effectiveness;
- Volume VII: Predicting Performance with Traffic Analysis Tools;
- Volume VIII: Work Zone Modeling and Simulation – A Guide for Decision-Makers;
- Volume X: Localized Bottleneck Congestion Analysis Focusing on What Analysis Tools Are Available, Necessary and Productive for Localized Congestion Remediation;
- Volume XI: Weather and Traffic Analysis, Modeling and Simulation; and
- Guide on The Consistent Application of Traffic Analysis Tools and Methods.
For situations when the HCM may not be appropriate it is possible to apply this Guide’s conceptual framework for evaluating travel time reliability to alternative analysis tools. The same conceptual approach of generating scenarios, assigning scenario probabilities, evaluating scenario performance, and summarizing the results applies when using alternative analysis tools, such as microsimulation, to estimate reliability effects of operations improvements.
Before embarking on the use of alternative tools for reliability analysis, the analyst should consider the much greater analytical demands imposed by a reliability analysis following this guide’s conceptual analysis framework. Thousands of scenarios may need to be analyzed using the alternative tool in addition to the number of replications per scenario required by the tool itself to establish average conditions. Extracting and summarizing the results from numerous applications of the alternative tool may be a significant task.
If a microscopic simulation analysis tool is used, a few of the adaptations of this Guide’s conceptual analysis framework that were fit to the HCM’s 15-minute Highway Capacity Manual 2010 will no longer be needed. Specifically:
- Scenarios may be defined differently and they may be of longer or shorter duration than those used in HCM analysis.
- Incident start times and durations will no longer need to be rounded to the nearest 15-minute analysis period.
- Weather start times and durations will no longer need to be rounded to the nearest 15-minute analysis period.
- Demand will no longer need to be held constant for the duration of the 15-minute analysis period.
- The peak-hour factors used to identify the peak 15-minute flow rate within the hour would no longer be applied. They would be replaced with the microsimulation model’s built-in randomization process.
- This Guide’s recommended freeway speed–flow curves for weather events and incidents would be replaced with adjustments to the model’s car-following parameters, such as desired free-flow speed, saturation headway, and start-up lost time. Unlike incidents, which the tool’s car-following logic can take care of, weather is modeled by adjusting the car-following parameters through weather adjustment factors before running the scenarios. Application guidance and typical factors are provided in the FHWA’s Traffic Analysis Toolbox (FHWA).
If a less disaggregate tool is used (e.g., mesoscopic simulation analysis tool, dynamic traffic assignment tool, demand forecasting tool), then many of this Guide’s adaptations of the conceptual analysis framework to the HCM may still be appropriate or may need to be further aggregated. The analyst should consult the appropriate tool documentation and determine what further adaptations of the conceptual analysis framework might be required to apply the alternative tool to reliability analysis.previous | next