Traffic Forecasts

Purpose

Traffic forecasting allows the state to make project decisions based on adequate structural and geometric capacity, financial and social viability, and environmental effects. Air, noise, energy, and other impacts vary with traffic levels. Typically, traffic volume projections are 20 years beyond the estimated date the project will open to traffic. Pavement type, such as bituminous or concrete, and strength are based on cumulative equivalent single axle load (ESAL) forecasts.

When to use this subject

You need traffic forecasts for construction projects on new alignment or reconstruction projects where pavement design in needed. Preservation projects are typically designed for current traffic volumes, therefore, traffic forecasts are not required unless requested.

Traffic forecasts frequently include alternative scenarios that lead to decisions regarding project viability and transportation policy. You may need updates if the letting date is delayed more than two years. Minor adjustments are made to reflect access changes as alternatives develop.

How this subject fits into the overall project development process

Different types of traffic forecasts are required at three different stages in project development.

Class I Actions: Environmental Impact Statement (EIS) — corridor studies

Traffic forecasts must be complete well before:

Scoping Documents (SD)
Scoping Decision Document (SDD)
Draft Environmental Impact Statement (DEIS)
Final Environmental Impact Statement (FEIS)

Class II Action: Categorical Exclusions (CATEX) — preliminary design

Traffic forecasts are not needed for preservation projects. Traffic forecasts must be completed before:

Pavement selection
Pavement design process

Class III Action (EA/EAW) — final design

Traffic Forecasts must be complete before the Environmental Assessment (EA).

If a Metropolitan Planning Organization (MPO) exists in the area, then traffic forecast discussions generally take place with the MPO when a project is first considered. Each MPO has a model that uses socioeconomic data to forecast traffic growth. MPOs do not have approval authority of trunk highway traffic forecasts, but typically do their own forecasts for the local system. The MPOs exist in urban areas where the population is greater than 50,000. Currently in Minnesota, there are seven MPOs:

Twin Cities
Duluth-Superior
Rochester
St. Cloud
Fargo-Moorhead
Grand Forks-East Grand Forks
La Crescent-La Crosse

StreetLight Insight can be used to estimate traffic volumes statewide and is especially helpful on roads where counts have not been obtained. StreetLight Insight is a web‐based software product that allows planners, modelers and engineers to flexibly run transportation analytics based on travel information gathered from multiple sources like smart phones and navigation devices in cars and trucks, also referred to as "Big Data." The ability to analyze trillion of trips derived from archival trace data allows transportation professionals to better plan for future needs.

Organizations involved

MnDOT:

Traffic Forecasting and Analysis Unit
Office of Traffic Engineering
Project Managers
District Traffic Forecasters
District Design
District Traffic
District Planning

FHWA