Mini Master Highlights

3: Traffic Data for Planning

Transportation planning is one of the major steps in the transportation project and program decision process. Planning decisions rely on traffic data to determine what, when, and where a project should be carried out.

Topic # 3-1: Highway Traffic Inventory

Highway inventory is the foundation for the transportation planning process. During the inventory process, data associated with existing roadways, such as the Annual Average Daily Traffic (AADT), types and classes of vehicles involved, speed, and travel time are collected. The Level of Service (LOS) per roadway segment is estimated.

Along with the Vehicle Miles Traveled (VMT) for a route or within an area, crash frequencies (e.g., # of crashes per 100 million VMT) are also frequently computed. These traffic data items, as listed below, provide the basic information on existing congestion and safety issues and serve as the starting point for future actions.

• Existing peak period traffic flow volume
• Existing AADT
• Existing peak period flow volume by vehicle class
• Estimated LOS
• Derived VMT

Topic # 3-2: Travel Demand Forecasting

While the Highway Inventory activity deals with existing traffic flows, Travel Demand Forecasting focuses on future travel demand - Future AADT. This forecast often relies on complex Travel Demand Modeling software enabled by a broad range of traffic data serving as inputs.

Traffic Generating and Attracting Rates

Number of trips a family, a household, or a person by different social and demographic factors like age, sex, income, education, occupation, and others on an annual basis. This data is typically gained from household travel surveys (e.g., FHWA's National Household Travel Survey).

Modal Choice Data

Modes travelers use to accomplish their trips: public transportation (bus, subways ...), private vehicles, walking, bicycling ... Modal Choice Data are also typically derived from household travel survey data.

Route-specific impedances

Speed, travel distance, travel time, toll from a trip's origin to destination are factors impacting travelers' decisions on route choices.

Inventory AADT Data

Past and existing AADT data are critical for travel demand model building, calibration, and validation.