Office of Operations
21st Century Operations Using 21st Century Technologies

Traffic Analysis Toolbox Volume III: Guidelines for Applying Traffic Microsimulation Modeling Software 2019 Update to the 2004 Version

Appendix B. Glossary

Alternative: A precise set of specific operational practices or transportation system enhancements represented and evaluated within a microsimulation analysis. The impact of each alternative is compared to other alternatives in the analysis based on key performance measures to inform transportation management decisions.

Base Model: An initial working version of the model prior to calibration.

Calibration: Process where the analyst selects the model parameters that cause the model to reproduce field-measured local traffic operations conditions the best.

Key Performance Measure: A measure of transportation system performance identified during the project scoping step and utilized in the alternatives analysis step to differentiate competing alternatives.

Methods and Assumptions Document: A key element of simulation analysis planning and management that documents key decisions coordinating analyst actions and project management.

Microsimulation: Modeling of individual vehicle movements on a second or sub-second basis for the purpose of assessing the traffic performance of highway and street systems. Microsimulation may also include the modeling of individual pedestrian movement.

Model: Specific combination of modeling software and analyst-developed input/ parameters used in analysis to represent the transportation system.

Model Variant: A variant of a base model altered to represent a specific travel condition in the transportation system.

Travel Condition: A combination of operational conditions and resulting system performance. Operational conditions are identified by a combination of demand levels and patterns (e.g., low, medium or high demand), weather (e.g., clear, rain, snow, ice, fog, poor visibility), incident (e.g., no impact, medium impact, high impact), and other planned disruptions (e.g., work zones, special events) that impact system performance (e.g., travel times, bottleneck throughput).

Software: The simulation tool used by the analyst in the development and application of a specific microsimulation model. Several models can be developed using a single software program. These models will share the same basic computational algorithms embedded in the software; however, they will employ different input and parameter values.

Tool: See Software.

Travel Time Reliability: Travel time reliability reflects the range of variation in travel times for trips taken between two locations at the same time of day over time. The lower the variation, the higher the travel time reliability. Travel time reliability is a key measure for travelers and transportation system users because a lack of travel time reliability implies that system users should budget significant amounts of additional time to ensure on-time arrival at trip destinations.

Validation: Process under which intrinsic tool-predicted traffic performance for a transportation system is compared against field measurements of traffic performance, such as traffic volumes, travel times, average speeds, and average delays. This report presumes that the software developer has already completed this validation of the software and its underlying algorithms in a number of research and practical applications.

Verification: Process where the software developer and other researchers check the accuracy of the software implementation of traffic operations theory. This report provides no information on software verification procedures.

Office of Operations