Chittenden County Transportation Modeling Glossary

Calibration

The process of developing the model parameters using observed transportation data.

 

Capacity

A transportation facility's (road, railway, etc.) ability to accommodate a moving stream of people or vehicles in a given time period.

 

Congestion

A condition which hinders movement on a transportation facility at optimal legal speeds. Frequently characterized by unstable traffic flows.

 

Decision Support System (DSS)

The DSS is a computer tool to analyze the interrelationships between transportation infrastructure and land use and development patterns.

 

Destination

The place to which a person travels or is sent.

 

Level of Service (LOS)

Refers to a standard measurement used by planners which reflects the relative ease of traffic flow on a scale of A to F with free-flow being rated LOS A and congested conditions rated as LOS F. More information at http://www.planning.org/thecommissioner/19952003/spring02.htm

 

Mode

A particular form of travel (eg., walking, bicycling, traveling by automobile, traveling by bus, or traveling by train).

 

Mode Split

The proportion of total person-trips using various modes of transportation.

 

Mode Choice

The form of travel (mode) chosen by individuals.

 

Network

1) In planning, a computerized representation of roadways and intersections that describes a transportation system.

2) In highway engineering, the configuration of highways that constitutes the total system.

3) In transit operations, a system of transit lines or routes, usually designed for coordinated operation.

 

Origin

The place from which a person travels or is sent.

 

Origin/Destination Study

A study of where person or vehicle trips begin and end. It may also include trip purposes and frequencies.

 

Peak Hour

The one hour period during which the roadway carries the greatest number of vehicles. Traffic impacts are typically evaluated during the morning and afternoon peak hours when the greatest numbers of motorists are traveling to and from work. It may be specified as the morning (AM) or evening (PM) peak.

 

Pedestrian Environmental Factor (PEF)

Identifies the pedestrian and bicycle-friendly parts of the transportation network.

 

Person-Trip

Trip made by a person from one location to another whether as a driver, passenger, or pedestrian.

 

Special Trip Generators

Employers with unique characteristics that are especially large and therefore need to be handled outside of the normal trip generation approach. Examples include: IBM (Essex and Williston), the University of Vermont, and Fletcher Allen Health Care.

 

Traffic Assignment

The process of predicting a specific path travelers take from their origin to their destination.

 

TransCAD

Computer software “platform” used for the CCMPO transportation model. More information at: http://www.caliper.com/tcovu.htm

 

Transportation Analysis Zone (TAZ)

The county is divided into 335 small areas. Each area has relatively similar characteristics within its boundaries. These areas are called Transportation Analysis Zones (TAZs). TAZs represent land use data on housing and employment in the modeling process.

 

Trip Distribution

The modeling process used to estimate the origins and destinations of travelers.

 

Trip Generation

The modeling process used to estimated the number and types of trips types taken by travelers (eg. Home to work, nonwork to home, etc.)

 

Validation

The process of evaluating the accuracy of the transportation model.

 

Vehicle Miles Traveled (VMT)

On highways, a measurement of the total miles traveled by all vehicles in the area for a specified time period. It is calculated by the number of vehicles multiplied by the miles traveled in a given area or on a given highway during the time period. One car traveling one mile represents 1 unit of VMT.

 

Volume-to-Capacity Ratio (V/C)

A measurement of the quality of roadway travel. The ratio of the existing amount of vehicular travel for a roadway to the amount of designed capacity on the roadway. A V/C ratio of 1 means the roadway is functioning at capacity and congested conditions are expected to occur.

 

 

Sources:

Puget Sound Regional Council, Seattle, WA

http://www.psrc.org/projects/mtp/glossary.pdf

http://www.psrc.org/projects/vision/2020glossary.htm

 

http://mcb.fhwa.dot.gov/glossary.asp

http://www.fhwa.dot.gov/environment/conformity/basic5gd.htm

http://www.planning.org/thecommissioner/spring02.htm