Transportation Research Synthesis:
Traffic Forecasting on Trunk Highways in
Nonmetropolitan Areas: A Survey of State
Practice
Presentation to MnDOT Technical Advisory Panel
Wednesday, September 26, 2012
1:00 p.m.
Christine Kline
Patrick C. Casey
CTC & Associates LLC
Madison, Wisconsin
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?

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 models
KY, MA, MD, MI, MN,
OR,TX
Only four states—Colorado, Illinois, Kansas and South Dakota—report no use
of modeling software to forecast traffic volumes.
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.
Socioeconomic Variable

Number of
Responses
Socioeconomic Variable
Number 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
Only four states—Colorado, Florida, Missouri and Nebraska—do not report the use of
socioeconomic variables in forecasting models.
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
Percentage
State (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.
 AZ applies different factors
Arizona
Nevada
Illinois
New Mexico
Kentucky
New York
Maine
North Dakota
Maryland
Oregon
Michigan
Wisconsin
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 Period
Number of
Responses
Time Period
Number 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 VMT
FL, 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?