the case for more moderate growth in vmt: a critical

The Case For More Moderate Growth in VMT:

A Critical Juncture in U.S. Travel Behavior Trends

Presentation for USDOT

Steven Polzin, Ph.D.Xuehao Chu, PhD., Lavenia Toole-Holt

November 3, 2004

2

Center for Urban Transportation ResearchThe University of South FloridaTampa, Florida

National Center for Transit Research (NCTR/UTC)Southeastern Transportation Center (STC/Southeastern

Region 4 UTC)National Bus Rapid Transit Institute (NBRTI)Established by the Florida Legislature in 1988

3

Context

An outgrowth of FDOT supported research:– Investigation of Florida Trends and Conditions – Exploration of the land use VMT relationship– Analysis of public transit implications of NHTS

A TRB paper that got out of hand.

Available online at http://nhts.ornl.gov/2001/articles/index.shtml

http://nhts.ornl.gov/2001/articles/index.shtml

4

Related Work

Charles Lave (1991) – Things Won’t Get a Lot Worse: The Future of U.S. Traffic Congestion, discussed effects of auto availability, labor force participation, age, income and vehicleavailability on the growth of VMT and congestion.Department of Energy (1995) – Reviewed VMT forecasting issues including age, income and licensure rates. Schaper and Patterson (1998) – Reviewed factors contributing to VMT growth.Department of Energy (2001) – Age and gender were used to model future VMT. FHWA (2002) – 2002 Status of the Nation’s Highways, Bridges, and Transit: Conditions and Performance, U.S. Department of Transportation, includes an estimate of VMT growth through 2020 documented in Vehicle Miles Traveled 2001.

5

Key Concepts

NHTS and Census data help paint a picture of what is going on regarding travel and travel behavior.

Several socio-demographic and transportation system performance trends are at critical juncture points.

We are seeing a slowing in the pace of VMT growth that will continue absent new intervening phenomenon.

Yet congestion may get worse.

The rate of trip making appears to be the single largest contributor to growing travel demand.

And there is much we do not yet know.

Conceptual Model of VMT Growth

DriversIndirect Drivers of Travel Behavior

Travel DemandPopulation1. Trip Rates2. Trip Distribution (length)3. Mode Selection4. Route/Path

Socio-Economic ConditionsHousehold/Person Characteristics

Economic ConditionsCulture/Values

Business Conditions

Land UseDensityMixUrban FormUrban DesignActivity ScaleContiguousness

Transportation SystemModal AvailabilityModal PerformanceCostSpeed/CongestionSafety, Reliability,

Convenience, etc.

Travel

Direct Drivers of Travel Behavior

Legal/Political Climate

Culture

Economy

Security

Family Structure

Institutional Structures

7

Household VMT Growth Outpaces Population Growth

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

1977 1983 1990 Adj. 1995 2001

All Persons (000) Household VMT (000,000)

Cars WorkersLicensed driversLane milesTrips

Source: U.S. Census Bureau, NHTS

8

Incremental Annual Growth in VMT

-40,000

-20,000

0

20,000

40,000

60,000

80,000

100,000

120,000

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

Mile

s in

Mill

iions Th

ruJu

ne 2

004

9

Annual Change in VMT and Population

Source: FHWA, Highway Statistics Series, Census population estimates

-4.00%

-2.00%

0.00%

2.00%

4.00%

6.00%

8.00%

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

VMT Percent Change

Five Year Average AnnualizedPopulation Growth Rate






Business Conditions



Convenience, etc.

Travel


11

U.S. Population is Concentrated in Peak Travel Age Cohorts

Source: CUTR analysis of NHTS and NPTS and U.S. Census Bureau

0

4,000

8,000

12,000

16,000

20,000

24,000

5-

5-9

10-

1415

-19

20-2

425

-29

30-3

435

-39

40-4

445

-49

50-5

455

-59

60-6

465

-69

70-7

475

-79

80-8

485

+

VM

T pe

r Cap

ita

0%

2%

4%

6%

8%

10%

12%

Per

cent

of P

opul

atio

n

VMT per Capita 2001 PMT per Capita 2001 1970 2000 2020

Population Age Profile in 2000

12

Average Household Size is Stabilizing, 1930-2000

4.013.68

3.38 3.29 3.112.75 2.63 2.59

0

1

2

3

4

5

1930 1940 1950 1960 1970 1980 1990 2000

Hou

seho

ld S

ize

.

Source: U.S. Census Bureau

13

Economies of Travel Beyond Two Member Households

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

1-person 2-persons 3-persons 4-or-more

Veh

icle

Mile

s

0

500

1,000

1,500

2,000

2,500

3,000

3,500

Vehi

cle

Trip

s

Miles Trips

Lower VMT per capitaHigher VMT per

capita

Source: CUTR analysis of NHTS

14

Households Size May Have Contributed to VMT Growth, 1940-2000

0%10%20%30%40%50%60%70%80%90%

100%

1940 1950 1960 1970 1980 1990 2000

Per

cent

of H

ouse

hold

s

1-person 2-person 3-person 4-person 5-or-moreSource: U.S. Census Bureau

15

Share of Population 16 Years of Age or Older with a Drivers License, 1970-2000

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1970 1980 1990 2000

% o

f Pop

ulat

ion

Ove

r 15

Yrs

with

Lic

ense

.

Male Female

Source: U.S. Department of Transportation, HSS and U.S. Census Bureau

16

We have reached Gender Equity in Licensed Drivers, 1963-2001

0%

20%

40%

60%

80%

100%

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

2001

Per

cent

of T

otal

Male Female

Source: FHWA, Highway Statistics Series

17

Older Women Less Likely to Drive

0102030405060708090

100

<= 1

9

20-2

4

25-2

9

30-3

4

35-3

9

40-4

4

45-4

9

50-5

4

55-5

9

60-6

4

65-6

9

70-7

4

75-7

9

80-8

4

Ove

r 85

Age Group

Per

cent

of D

river

s

Male Female

Source: FHWA, Highway Statistics Series, 2000

18

Vehicle Saturation? Vehicle Gluttony?

00.20.40.60.8

11.21.41.6

1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001

Rat

io

Ratio of Vehicles to Persons Over 16Ratio of Vehicles to DriversRatio of Vehicles to Workers

Source: FHWA, Highway Statistics Series

19

Declining Zero-Vehicle Households

0%

5%

10%

15%

20%

25%

1960 1970 1980 1990 2000

Per

cent

NPTS/NHTS Census

Source: CUTR analysis of NHTS and NPTS and U.S. Census Bureau

20

Percent Teen Auto “Ownership”

20031999

58

45Total

17

15Total UsedNewUsedNew

Source: Teenage Research Unlimited, Associated Press, September 14, 2003.

471112518-19

36914116-17

Teens with Auto Available (percent)

Age

21

Commute Times Are Growing

22.421.7

25.5

0

5

10

15

20

25

30

1980 1990 2000

Min

utes

of T

rave

l

Source: CTPP 2000 and prior

22

Travel Time Budgets Have Grown 1.8 Minutes per Day per Person per Year

45.7

58.2

78.5

66.2

0

10

20

30

40

50

60

70

80

90

1982 1987 1992 1997 2002

Min

utes

of T

rave

l per

Day

32.8 more minutes of travel each day since 1983

Source: CUTR analysis of NHTS and NPTS

23

Change of Time Spent by Major Time Use Category from 1965 (Minutes per Day)

-60

-40

-20

0

20

40

60

80

1965

1970

1975

1980

1985

1990

1995

2000

Min

utes

per

Day

Cha

nge

from

196

5

Family Care Work and Commute Personal Care Free Time

Why?Fewer kidsTechnologySpecialization of labor

Source: Americans’ Use of Time Project cited in Robinson, 1999 and 1998-2001 Time Diary Studies






Business Conditions



Convenience, etc.

Travel


25

How Does Land Use influence Travel?

Impact on VMT

Land Use TraitsDensityMixUrban FormUrban DesignActivity ScaleContiguousness

Travel Demand Impact of “Better” Land Use

Trip Rates …………………. Greater accessibility will tend to encourage trip making

Trip Distribution (length) ……Greater accessibility will tend to reduce trip length

Route/Path …………………..Greater accessibility will tend to produce shorter trips

Mode Choice ………………..Greater accessibility and density enables competitive alternative modes






Business Conditions



Convenience, etc.

Travel


27

Share of Urban VMT by Road Type, 1966-2001

0%10%20%30%40%50%60%70%80%90%

100%

1966

1968

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

Sha

re o

f Urb

an V

MT

.

Urban Interstate Other Urban Roads

Source: FHWA (Note: Urban Interstate share after 1980 includes Other Urban Freeways and Expressways)

28

NHTS/NPTS Data Suggest Travel Speeds are Now Slowing

0

5

10

15

20

25

30

35

40

1977 1982 1987 1992 1997 2002

Spe

ed (M

PH

)

All Trips Work Trip Usual Mode

Changes in mode, path, departure time, and moving to the suburbs enabled higher speed travel

Have we run out of ways to travel faster?


29

VMT per Person Hour Spent in Travel is Declining

15.7

19.8

17.215.0

20.0

0

5

10

15

20

25

1977 1982 1987 1992 1997 2002

VM

T pe

r Per

son

Hou

r .

Composite effect of mode and speed


30

Are Income and Travel Cost Driving VMT Growth?

$0.59

$0.36 $0.31 $0.34

$15,288 $14,983$13,468

$17,270

$0.00$0.10$0.20$0.30$0.40$0.50$0.60$0.70$0.80$0.90$1.00

1984 1986 1988 1990 1992 1994 1996 1998 2000 2002

POV

Exp

endi

ture

/VM

T (c

ents

per

mile

, 200

1 $)

$0$2,000$4,000$6,000$8,000$10,000$12,000$14,000$16,000$18,000$20,000

Inco

me

per P

erso

n (2

001

dolla

rs)

POV Expenditure per VMT (cents per mile)Income per Person (2001 Dollars)

Source: CUTR analysis of NHTS, BLS





Business Conditions Direct Drivers of Travel Behavior



Convenience, etc.

Travel


32

VMT Growth Estimation Equations

Trip Generation Trip Length Mode

Miles VehicleMilesPerson Miles Vehicle

TripsPerson MilesPerson

PersonTripsPerson Population ≡×××1.

Travel Time Budget Travel Speed

Miles VehicleTravel of HoursPerson

MilesVehiclePerson

Travel of HoursPerson Population ≡××2.

33

Key Indicators, 1977 to 2001

% Change 1977-2001

20011977

+30.1%277,208213,141All Persons (000)

+115.9%234,994108,826HH VT (000,000)

+151.4%2,281,863907,603HH VMT (000,000)

+94.1%410,969211,778Person Trips (000,000)

+114.3%4,026,1581,879,215PMT (000,000)

+49.2%1,483994PT/P/Year (trip rate)

+17.4%

+10.4%

0.5670.483VMT/PM (mode)

9.7978.874PMT/PT (trip length)


34

Factors Contributing to US VMT Growth 1977-2001

Trip Length10%

Mode Shifts16%

Trip Frequency

46%

Population28%


35

Person Trips per Person per Year and PMT per Person Trip


978

1,272

994

1,457 1,483

9.3 9.0 9.88.9 8.7

0

500

1,000

1,500

1977 1980 1983 1986 1989 1992 1995 1998 2001

PT

per P

erso

n pe

r Yr

0

5

10

15

PM

T pe

r PT

PT/Person/Yr PMT per PT

Trip Rate

Trip Length

36

Daily Person Trip Rates by Vehicle Availability, 2001

4.37 4.18 4.33.75

3.372.75

0

1

2

3

4

5

MoreVehicles

Than Adults(23.3% of

Pop)

VehiclesEquals

Adults, 1Adult HH(43.5% of

Pop)

VehiclesEquals

Adults, MultiAdult HH(8.4% of

Pop)

One LessVehicle Than

Adults(15.9% of

Pop)

Over OneLess VehicleThan Adults

(3.9% ofPop)

No Vehicles(5.1% of

Pop)

Trip

Rat

es


Vehicle “Shortage” Households

37

Daily Mileage by Vehicle Availability and Mode, 2001

Per Capita Daily Mileage by Mode

0 10 20 30 40 50 60

More Vehicles Than Adults (23.3% of pop.)

Vehicles Equals Adults, 1 Adult HH (43.5% of pop.)

Vehicles Equals Adults, Multi-Adult HH (8.4% of pop.)

One Less Vehicle Than Adults (15.9% of pop.)

Over One Less Vehicles Than Adults (3.9% of pop.)

No Vehicles (5.1% of pop.)

POV-Driving POV-Passenger Transit Walking Other


38

Declining Walk Shares

5.0% 4.6% 4.1% 3.7%2.6% 2.8%

2.9%

4.0%4.5%

2.3%

0%

2%

4%

6%

8%

10%

12%

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Per

cent

Wal

king

to W

ork

Work Trip by "Usual Mode" Work Trip by Actual Mode Census Walking to Work

Source: CUTR analysis of NHTS and NPTS, U.S. Census Bureau

39

Ending the Decline in Transit Mode Share – Survey Data

4.7%5.3%

8.9%

6.4%

4.9%5.0%

3.4%2.7% 2.7%

2.2% 1.8% 1.6%

4.5% 4.6%

3.6% 3.7%

4.7%

4.9%

4.6%4.1%4.6%

0%1%2%3%4%5%6%7%8%9%

10%

1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999 2002

Perc

ent o

f Trip

s on

Tra

nsit

Census Journey to Work Census Supplemental Survey-WorkNPTS/NHTS (all trips) NPTS/NHTS (work trips)AHS (work trips)

40

Transit Share in Person Miles –Empirical Data

Person Mile Travel Based Transit Mode Share

1.20

%

1.17

%

1.12

%

1.07

%

1.03

%

1.00

%

1.09

%

1.07

%

1.05

%

1.04

%

1.01

%

1.01

%

1.05

%

1.01

%

0.0%

0.2%

0.4%

0.6%

0.8%

1.0%

1.2%

1.4%

1.6%

1.8%

1988 1990 1992 1994 1996 1998 2000 2002 2004

Tran

sit M

ode

Sha

re P

erce

nt

(per

son

mile

bas

ed)

Through June 04, VMT is up approximately 2% and transit use is up approximately 0.5%

?

Source: CUTR analysis of NHTS, NPTS, FHWA, and APTA data

41

Census Work Trips Carpooling Mode Share

20.4% 19.7%

12.2%13.4%

0%

5%

10%

15%

20%

25%

1970 1980 1990 2000

Perc

ent C

arpo

olin

g to

Wor

k

Source: U.S. Census Bureau

42

Stabilizing Vehicle Occupancies –NHTS and NPTS

0.00.20.40.60.81.01.21.41.61.82.0

1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001

Occ

upan

cy

Work Trip All Trips


43

Slowing Vehicle Miles of Travel Per Person Mile of Travel

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1977 1983 1990 1995 2001

VM

T/P

MT

Composite effect of mode choices


44

So What Does this Mean in Terms of VMT?

45

VMT Growth Estimation Equations

Trip Generation Trip Length Mode

Miles VehicleMilesPerson Miles Vehicle

TripsPerson MilesPerson

PersonTripsPerson Population ≡×××1.

Travel Time Budget Travel Speed

Miles VehicleTravel of HoursPerson

MilesVehiclePerson

Travel of HoursPerson Population ≡××2.

46

VMT Growth Scenario 1

30%49%

10% 17%

151%

22% 16% 8% 5%

60%

0%20%40%60%80%

100%120%140%160%

Population Person Tripsper Person

Person Milesof Travel perPerson Trip

Vehicle Milesof Travel perPerson Mile

Total PersonVMT

Per

cent

Incr

ease

1977-2001 2001-2025

47

VMT Growth Scenario 2

151%

57%65%

30%

17%

55%

22%

-18%

-30%-15%

0%15%30%45%60%75%90%

105%120%135%150%165%

Population Travel Time perCapita

Vehicle Miles perPerson Hour

Total Person VMT

Perc

ent I

ncre

ase

1977-2001 2001-2025

48

Future VMT Growth

Vehicle Miles Traveled 2001 – 2.08% per year (to 2020)

Scenario One – 1.98% per year (to 2025)

Scenario Two – 1.90% per year (to 2025)

49

Observations

The moderation of several historic trends may have significant impacts in terms of future VMT demand as well as on other aspects of travel behavior.

Socio-Economic Conditions• Average Household Size• Women Labor Force Participation Rates• Women Share of Licensed Drivers • Share of Zero Vehicle Households

Transportation System• Travel Speed

Travel Trends• Mode Share of Public Transportation• Vehicle Occupancies• Mode Share for Walk, Bike• Perhaps trip rates

50

Observations (Transportation Supply)

Increases in system capacity (supply) compared to demand growth remains uncertain.

– What will federal, state and local willingness to increase spending be?

– Will there be the public will to tolerate the impacts of transportation system expansion?

– What role will toll facilities play?

– What increase in transit supply and use will occur?

– What capacity benefits will be realized by ITS?

51

Observations (travel behaviors)

The dynamic response of our system subject to growing demand is not well understood.

How will people adapt?Communications substitutionTemporal shifts in demandLocation shifts to avoid congestion“Fragileness” of our system

Where are we on this HCM curve?

52

Observations & Speculations

The growth in trip making and travel time budgets poses the greatest risk to moderating travel demand.

– Historic causal variables of income, car ownership and worker status are no longer the dominant drivers of trip making (we no longer know how to forecast trip generation growth?)

– Multi-tasking moderates the reluctance to travel:Eating in carCell phone use

– Activities are shifting from inside to outside of home:Specialization of labor (eating out, hired services)Socialization (for working Americans the social relationships have moved

from the front porch or back yard to the workplace break room) Parenting (more organized youth activities and lessons)Specialization of services (GP Dr. > specialist > lab > scanning center)

– Land use changes will not impact the trip making

53

Observations

Uncertainties include:– Energy costs and traveler reactions– The extend to which development trends change

toward smart growth (retrofit versus new town)

– The extent to which housing affordability encourage housing dispersion

– Whether activity scale continues to influence travel (mega churches, schools, and stores, create longer trips and different social relationships)

– What will the VMT trends for truck travel be?– What will the VMT trends for long distance travel be?– Can/will peak spreading continue?

54

Socio Demographic Research Questions

How are older American travel rates likely to change over time? Of zero vehicle households what share are by choice, what share have income constraints, what share have mental or physical health or legal constraints?Under what conditions do multi-person households result in some economy of travel?What happened to the concept of a travel time budget? Are we multitasking in our cars?

55

Transportation System Performance Research Questions

Has the increase in congestion occurred so fast as to

preclude location decision making from naturally

adjusting to intolerable travel times?

Have we really reached the point where average

daily travel speeds are declining?

To what extent is real income and travel cost, versus

time a constraint on additional travel?

56

Trip Generation, Distribution and Mode Choice Research Questions

Will trip making levels increase?Will trip lengths continue to grow or accelerate?Is transit growth inevitable?Will walk see a revival as a functional travel mode?Will auto occupancies stop declining?

What Will Happen Next?

Steven E. Polzin, Ph.D.Center for Urban Transportation ResearchUniversity of South Florida4202 Fowler Avenue, CUT100Tampa, Florida [email protected]

Available online at http://nhts.ornl.gov/2001/articles/index.shtml

mailto:[email protected]

http://nhts.ornl.gov/2001/articles/index.shtml

the case for more moderate growth in vmt: a critical

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