Traffic Forecasting on Trunk Highways in Nonmetropolitan Areas: A Survey of State Practice

Presentation to MnDOT Technical Advisory PanelWednesday, September 26, 20121:00 p.m.

Christine Kline Patrick C. CaseyCTC & Associates LLCMadison, Wisconsin

Transportation Research Synthesis:

Background

Traffic forecasting plays a critical role for MnDOT in corridor planning, geometric design, pavement design, safety analysis, access management and more.

In previous decades, Minnesota has seen steady growth in vehicle miles traveled.

In recent years, VMT growth in Minnesota has been flat and declined by 0.5% from 2009 to 2010.

TRS project scope

MnDOT’s Office of Transportation Data & Analysis wanted to know: How other states are dealing with what appears

to be a nationwide trend in a leveling off or decline in VMT.

The forecasting methods used by other state DOTs to project traffic volumes in nonmetropolitan areas with a population under 50,000.

Technical Advisory Panel

Shirlee Sherkow, Project Coordinator Chu Wei, Technical Liaison

Technical Advisory Panel Members

Lynne Bly Jim Miles

Gene Hicks Tom Nelson

Jason Junge Paul Stine

James McCarthy

Methodology

We distributed an online SurveyMonkey survey to members of the AASHTO Standing Committee on Planning. Nine-question survey, reviewed and approved by the

TAP, of open-ended and multiple-choice questions

July 30 email announced the survey, with two weeks for responses (August 10 survey deadline)

August 7 reminder email encouraged more responses

September 7 final draft of report sent to TAP

Methodology

The survey gathered information in four key areas: Methodologies and tools used to estimate future

traffic volumes

Data and factors used in forecasting

Projection time periods

Flattening or decrease in VMT

Survey response

Thirty states provided survey responses.

Survey Respondents

Arizona Massachusetts North Carolina

Colorado Michigan North Dakota

Connecticut Minnesota Oregon

Florida Mississippi Pennsylvania

Illinois Missouri South Dakota

Iowa Montana Texas

Kansas Nebraska Utah

Kentucky Nevada West Virginia

Maine New Mexico Wisconsin

Maryland New York Wyoming

Survey response

Rhode Island provided an email response All planning is performed by the state’s metropolitan

planning organization; Rhode Island DOT has no forecasting procedures for nonmetropolitan areas

Not all respondents answered every question Percentages noted in survey results are adjusted

accordingly

Survey results

Question 1: Please indicate the methodology(ies) used in your agency’s program to estimate future traffic volumes.

Regression Models State

Box-Cox linear regression WI

Cubic regression NM

Least squares regression AZ, KS, NM, PA

Linear regression AZ, CT, FL, IA, IL, KS, KY, MA, ME, MI, MN, MO, MS, MT, NC, ND, NE, NV, NY, OR, SD, TX, UT, WI, WV, WY

Logistic regression AZ, WI

Multinomial regression (for mode split) CT

Nonparametric regression FL, KY

Survey results

Question 1: Please indicate the methodology(ies) used in your agency’s program to estimate future traffic volumes. All responding states but four—Colorado, Maryland, New Mexico and Pennsylvania—use linear regression models to estimate future traffic volumes. Seven states make use of multiple regression models:

Arizona (least squares, linear, logistic) Connecticut (linear, multinomial) Florida (linear, nonparametric) Kansas (least squares, linear) Kentucky (linear, nonparametric) New Mexico (cubic, least squares) Wisconsin (Box-Cox, linear, logistic)

Survey results

Question 1: Please indicate the methodology(ies) used in your agency’s program to estimate future traffic volumes. Respondents reported other methodologies used to forecast traffic volumes, including:

Growth rate from similar sites (Nevada)

Historical trend analysis (Colorado)

Linear or parabolic growth rates based on the knowledge of local growth patterns (Maryland)

Statewide or travel demand models (Arizona, Maine, Massachusetts, North Carolina, Oregon, Wisconsin)

Survey results

Question 1a: Does your agency use a modeling software program to estimate future traffic volumes?

Only four states—Colorado, Illinois, Kansas and South Dakota—report no use of modeling software to forecast traffic volumes.

Vendor Model/Program State

Caliper Corporation TransCAD IA, MS, MT, NV, WY

Citilabs Cube Voyager MD, ME, NY, UT

Cititlabs TP+ (legacy system) MD, WI

Citilabs Tranplan (legacy system) CT

IHS Global Insight Statewide VMT macroeconomic model NY

PTV America VISUM NM

Not specified Statewide or travel demand modelsKY, MA, MD, MI, MN, OR,TX

Survey results

Question 2: How many years of historical data does your agency use when forecasting future traffic volumes?

Survey results

Question 3: Please indicate the social and economic variables included in your agency’s traffic forecasting methodology.

Only four states—Colorado, Florida, Missouri and Nebraska—do not report the use of socioeconomic variables in forecasting models.

Socioeconomic VariableNumber of Responses

Socioeconomic VariableNumber of Responses

Total population 22 Unemployment rate 3

Employment 21 Motor vehicle registration 3

Households 21 Fuel consumption 2

Personal income 9 Driving age population 2

Labor force 6 Population age 16 and over 2

Gas prices 4 Population age 65 and over 2

Survey results

Question 3a: If socioeconomic variables are included in your agency's traffic forecasting methodology, please describe how they are employed.Socioeconomic variables most often serve as inputs to respondents’ travel demand or statewide models.

Socioeconomic variables are also used to: Analyze trends.

Determine impact on current traffic.

Determine trip generation/trip distribution/trip attraction.

Develop growth profiles.

Influence choice of growth rate.

Survey results

Question 4: When forecasting traffic volumes, does your agency apply minimum and maximum growth factors?

States Using Minimum Growth Factors States Using Maximum Growth Factors

State (14)Factor

PercentageState (8)

Factor Percentage

AZ, MS, ND, NM None specified AZ, MS, NM, WV None specified

OR 0% MA 1.5%

KS, MA, ME, MN, NV, WI 0.5% MN 3%

MO 0.5 % to 1% MT 3.5%

MT 1% TX 5%

TX 2%

Survey results

Question 5: Does your agency apply different growth rates to heavy commercial traffic versus total traffic volume?Twelve states apply different growth rates to heavy commercial traffic and total traffic volume.

Arizona Nevada

Illinois New Mexico

Kentucky New York

Maine North Dakota

Maryland Oregon

Michigan Wisconsin

AZ applies different factors at statewide modeling level, not at a micro level.

NV has four methods for truck forecasting.

NM uses data from FAF3 to forecast truck trips.

OR uses different factors for its statewide integrated freight model.

Survey results

Questions 6 and 6a: Please indicate the time periods included in your agency’s projections of future traffic volumes and describe why these time periods were selected.

Time PeriodNumber of Responses

Time PeriodNumber of Responses

20 years 26 5 years 6

10 years 14 40 years 5

30 years 12 35 years 4

25 years 10 50 years 1

15 years 8

Reasons for selecting time periods:Pavement/project design (12 states)

Required for long-range transportation plan (4 states)

FHWA standards (3 states)

Required for statewide model (3 states)

Survey results

Question 7: Has your state experienced a flattening or decrease in VMT in nonmetropolitan areas?Twenty-three states are experiencing a flattening or decrease in VMT; seven states are not.

Yes Reponses No Responses

Arizona, Colorado, Connecticut, Illinois, Iowa, Kansas, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, Nevada, New York, North Carolina, Oregon, Pennsylvania, Utah, West Virginia, Wisconsin

Florida, Montana, New Mexico, North Dakota, South Dakota, Texas, Wyoming

Survey results

Question 8: If your state has experienced a flattening or decrease in VMT in nonmetropolitan areas, is your agency considering changes in the methodology used to forecast traffic volumes, or have changes already been adopted?

Description of Traffic Forecasting Program State

Flattening or Decrease in VMT and Considering Forecasting Changes

CT, IA, IL, KS, KY, MA, MI, MN, NC, NY, OR

Flattening or Decrease in VMT and Not Considering Forecasting Changes

AZ, CO, MD, ME, MO, MS, NE, NV, PA, UT, WI, WV

No Flattening or Decrease in VMTFL, MT, ND, NM, SD, TX, WY

Survey results

Question 8: If your state has experienced a flattening or decrease in VMT in nonmetropolitan areas, is your agency considering changes in the methodology used to forecast traffic volumes, or have changes already been adopted?

States are considering or making changes in:

Growth rates

Statewide models

Summary Thirty-one states responded to our request (30 online

surveys completed) Most of the responding states use linear regression models

to estimate future traffic volumes. Less commonality is found in the software models states use

to estimate future traffic volumes. Most respondents use socioeconomic variables, most often

as inputs to travel demand or statewide models. Survey results indicate that many other states are also

experiencing a flattening or decrease in VMT. Almost half of these states are considering or implementing changes in

forecasting methods.

Thank you!

Questions?

Thank you!

Questions?