3. Vehicle Miles Traveled

This chapter presents information on household vehicle usage, as measured by the number of vehicle miles traveled

(VMT). VMT is one of the two most important components used in estimating household vehicle fuel consumption.

(The other, fuel efficiency, is discussed in Chapter 4). In addition, this chapter examines differences in driving

behavior based on the characteristics of the household and the type of vehicle driven. Trends in household driving

patterns are also examined using additional information from the Department of Transportation’s Nationwide Personal

Transportation Survey (NPTS).

Household VMT is a measure of the demand for personal transportation. Demand for transportation may be viewed

from either an economic or a social perspective. From the economic point-of-view, the use of a household vehicle

represents the consumption of one consumer good to secure other goods or services: household members drive to

work, to shop, for recreation, or to socialize. The social perspective takes into account the makeup of the household

and the motivation for each vehicle trip.

Total and Average Vehicle Miles Traveled

In 1991, household vehicles traveled a total of just over 1.6 trillion miles, up by 91 billion miles (6.0 percent) since

1988 (Table 5). This represents an annual increase of only 2.0 percent, which is substantially slower than in the

early 1980’s (between 1983 and 1988, annual growth averaged about 4.5 percent). The total increase since 1983

(32 percent) corresponds to an average annual increase of 3.5 percent per year.

Table 5. Annual Percent Change in Vehicles and Vehicle Miles Traveled, 1983, 1985, 1988, 1991

Survey Year Survey-to-Survey Annual Percent

Change

Overall

1983 1985 1988 1991 1983 to

1985

1985 to

1988

1988 to

1991

1983 to

1991

Number of Households

(million) .................. 84.4 87.3 91.6 94.6 1.7 1.6 1.1 1.4

Number of Households with

Vehicles

(million) .................. 72.2 77.7 81.3 84.6 3.7 1.5 1.3 2.0

Real Disposable Personal

Income

(billion $1987) .............. 2894 3162 3404 3535 4.5 2.5 1.0 2.4

Number of Household Vehicles

(million) .................. 129.3 137.3 147.5 151.2 3.0 2.4 0.8 2.0

Vehicles Miles Traveled

(billion) ................... 1215 1353 1511 1602 5.5 3.8 2.0 3.5

Vehicle Miles Traveled per

Household with Vehicles

(Thousand) ................ 16.8 17.4 18.6 18.9 1.7 2.2 0.6 1.5

Energy Information Administration/Household Vehicles Energy Consumption 1991 15
Vehicle Miles Traveled per

Vehicle

(Thousand) ................ 9.4 9.9 10.2 10.6 2.4 1.3 1.3 1.5

Sources: Energy Information Administration, Office of Energy Markets and End Use, 1983, 1985, 1988, and 1991 Residential

Transportation Energy Consumption Surveys; U.S. Bureau of Economic Analysis, Survey of Current Business Population, March 1992.

The relatively slower growth since 1988 can be traced to both the downturn in the economy and underlying longerterm social changes that have affected households and their members. The growth in household vehicle miles

traveled typically averages about 1 percentage point above the growth in real disposable personal income (personal

income adjusted for inflation). The 3.5 percent overall annual growth in VMT between 1983 and 1991 compares

to 2.4 percent growth in disposable personal income over the same time period. The 2.0 percent growth in VMT

between 1988 and 1991 compares to a 1.0 percent growth rate for personal income (Table 5).

In 1991, there were more than 150 million household vehicles in nearly 85 million U.S. households (about 90 percent

of all households). U.S. households with vehicles drove, on average, about 10,600 miles per vehicle and 18,900

miles per household (Figure 6). Two key factors affecting how much individual households drive are the number

of drivers and the presence of children in the household. The following sections examine the effect of these and

other factors (such as the number of drivers and household income) on household VMT.

Figure 6. Household and Vehicle Miles Traveled by Survey Year

Source: Energy Information Administration, Office of Energy Markets and End Use, 1991 Residential Transportation Energy

Consumption Survey.

16 Energy Information Administration/Household Vehicles Energy Consumption 1991
The Effect of Household Composition

VMT per Household VMT per Vehicle

1983 1985 1988 1991

Survey Year

0

2

4

6

8

10

12

14

16

18

20

Vehicle Miles Traveled (thousands)

16.8

9.4

17.4

9.9

18.6

10.2

18.9

10.6

VMT per household and VMT per vehicle growth rates have slowed since 1988 due to lower economic growth.

Measurement of Vehicle Miles Traveled (VMT)

The annual VMT for each vehicle in the RTECS was either (1) calculated using two odometer readings or (2)

imputed using a regression estimate. For each vehicle in the sample, the RTECS collects a beginning-of-year

and an end-of-year odometer reading. VMT equals the difference between the two readings, adjusted to reflect

a 365-day year. For vehicles that were in the household less than a full year, the mileage was adjusted to

reflect the amount of time the household was in possession of the vehicle. For vehicles that were missing one

or both odometer readings, a regression estimate was used to estimate the annual mileage. For a vehicle that

was not used by the household for the full year, the regression estimate was adjusted downward to reflect the

amount of time the vehicle was in the household. The total VMT, representing the number of miles traveled

nationally for all residential vehicles, is equal to the weighted sum of the individual VMT for each vehicle.

(See Appendix B, "Estimation Methodologies," and Appendix C, "Quality of the Data," for further discussion

about the annual VMT.)

Energy Information Administration/Household Vehicles Energy Consumption 1991 17
Average household driving varies extensively depending on the makeup of the household:

Households with children drove 22,800 miles on average, compared with 16,500 miles in households with

no children.

Households with 16- or 17-year-old children drove more than any other major group (28,000 miles), about

7,000-8,000 miles more than households with younger children.

In households without children, VMT ranged from 10,600 miles in single adult households to 19,700 miles

in households with two or more adults.

In single-driver households without children, VMT ranged from a low of 7,300 miles for drivers at least

60 years old to 14,200 miles for drivers under 35 years old.

Excluding households with 16- or 17-year old children, the remaining households with children still

averaged 21,700 miles, about 5,000 miles more than households without children; the difference being the

presence of adults over 60 years of age2. If they are excluded, then households with young children drive

less than households with at least two adults and no children. In other words, the households that do the

most driving are those with two adults, no children and a head of household younger than 60 years of age.

2

Households in which the head of household was at least 60 years old. All household ages refer to the head of household, as

stated in the RECS.

18 Energy Information Administration/Household Vehicles Energy Consumption 1991
The Effect of the Number of Drivers

In 1991, VMT averaged 10,000 miles per driver in households with no children, and 1,000 to 2,000 miles higher

in households with children, depending on the age of the children (Figure 7). These averages apply to households

with up to three drivers. In households with four or more drivers, the presence of children (regardless of their age)

implied fewer miles per driver. There are two likely explanations. One is that these households included one or

more younger or older adult drivers, who tend to drive less than average. A second, and related consequence of the

first, is that the number of vehicles does not keep pace with the number of drivers. The data also indicates that it

is equally likely that households with three drivers have two or three vehicles; and those with four drivers are only

slightly less likely to have three rather than four vehicles. Thus VMT cannot keep pace with drivers in larger

households with more than three drivers.

Figure 7. Average Household Vehicle Miles Traveled and the Number of Drivers

Source: Energy Information Administration, Office of Energy Markets and End Use, 1991 Residential Transportation Energy

1 2 3 4 or more Average Number of Drivers

0

5

10

15

20

25

30

35

40

45

Miles Traveled per Household (thousands

16.5

22.8 Children

No Children

Household miles driven are proportional to the number of drivers. The presence of children implies more trips

and thus more VMT per household. Very large households are an exception.

Consumption Survey.

Energy Information Administration/Household Vehicles Energy Consumption 1991 19
The Effect of Household Income

VMT per household increases with household income (Figure 8).

For every additional $10,000 of income, vehicle miles traveled increased by approximately 3,000 miles.

Within each income category, the presence of children added 3,000 to 5,000 miles per household.

Households with annual incomes of $35,000 or more drove about twice as many miles per household as

those earning less than $15,000.

Household income is more likely to increase with household size, so also is the number of drivers. Thus it is

plausible that income and drivers are correlated. For example, more drivers would imply more household members

in the work place and consequently a higher household income.

Figure 8. Average Household Vehicle Miles Traveled and Income

Source: Energy Information Administration, Office of Energy Markets and End Use, 1991 Residential Transportation Energy

0 10 20 30 40 50 60 70 80

0

5

10

15

20

25

30

35

Miles Traveled per Household (thousands

Household VMT increases with income. It is higher for households with children than households without.

Children

No Children

Average Family Income (thousand dollars)

Consumption Survey.

20 Energy Information Administration/Household Vehicles Energy Consumption 1991
Energy Information Administration/Household Vehicles Energy Consumption 1991 21
The Effect of Driver Age

VMT per vehicle is also related to the age of the driver in the household (Figure 9).

VMT per vehicle increases with age of the primary driver into the 30’s, averages more than 12,000 miles

per year through the 40’s, then declines. The youngest primary drivers probably drive less because they

are less likely to have children (which adds to driving distances in other age categories), and are also less

likely to have to go to work.

Primary drivers in their 80’s drive the least (an average of less than 6,000 miles).

Figure 9. Average Vehicle Miles Traveled per Vehicle and Age of Primary Driver

Source: Energy Information Administration, Office of Energy Markets and End Use, 1991 Residential Transportation Energy

10 20 30 40 50 60 70 80 90

Age of Primary Driver

0

2

4

6

8

10

12

14

16

Miles Traveled per Vehicle (thousands)

16-17

18-22

23-29 30-39 40-49

50-59

60-69

70-79

80+

VMT per vehicle generally decreases with the age of the primary driver, with the exception of the 

youngest primary driver groups who are less likely to have children and thus drive less.

Consumption Survey.

22 Energy Information Administration/Household Vehicles Energy Consumption 1991
The Effect of Vehicle Age

The number of miles driven in a vehicle appears to be inversely proportional to the age of the vehicle (Figure 10).

The newest vehicles in the survey (model years 1991 and 1992) were driven twice the number of miles per vehicle

as the oldest vehicles (the pre-1977 models). This is not surprising, as new vehicles are typically cheaper to run,

more comfortable, and more reliable than older vehicles.

Approximately 85 percent of the oldest vehicles (pre-1977 model year) were in households with more than one

vehicle. In such a household, an older vehicle typically is not the household’s primary vehicle, and is therefore

driven less than the primary (probably newer) vehicle.

Another factor may be that older households tend to hold on to their vehicles longer and older households drive less

than younger households. Thus older vehicles are in part associated with the age of the primary household member.

Figure 10. Average Vehicle Miles Traveled and Vehicle Age

Source: Energy Information Administration, Office of Energy Markets and End Use, 1991 Residential Transportation Energy

1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992

Model Year

0

2

4

6

8

10

12

14

16

Miles Traveled per Vehicle (thousands)

Newest

Oldest

Before 1973

1974-1976

1977-1979

1980-1982

1983-1985

1986-1988

1989

1990

1991-1992

VMT per vehicle varies by model year due to several factors including the cost and benefits of driving 

newer vehicles, the number of vehicles sold in that year, and the age of drivers in the household.

Consumption Survey.

Energy Information Administration/Household Vehicles Energy Consumption 1991 23
24 Energy Information Administration/Household Vehicles Energy Consumption 1991
The Effect of Region

Regional differences in VMT are of particular interest when considering gasoline tax issues. The debate over the

proposed increase in the gasoline tax in the fiscal year 1994 budget suggested that households in the South and West

Regions (where cities are fewer and more widely separated) drive further distances than in other regions. Although

the 1991 RTECS identified some differences among regions, none of the variation was statistically significant.

Figure 11 shows the average per household VMT by Census region. Of greater interest is the wide variation within

each region, as indicated by the standard errors associated with the RTECS data. On average, metropolitan

households drive about 900 miles more each year than nonmetropolitan (generally rural) households (20,400 miles

per household compared with 19,500 miles in rural areas). As would be expected, central city households drive the

least on average (only 15,900 miles).

Rural refers to all nonmetropolitan areas in the United States, for example, those not in a Metropolitan Statistical

Area, and it is not meant to imply farm or ranch types exclusively. However, there are limited data in the survey

from respondents that could be classified as "farm operations," those that were more than one acre in size and had

$1,000 or more in sales in the year. Because of the wide variation in this limited number of cases, their average

household VMT of 29,000 is not statistically different from the smaller average of 19,500 for all rural households.

It is likely, however, that these farm operations have a higher annual VMT than nonfarm households at the national

level.

Figure 11. Average Household Vehicle Miles Traveled and Census Regions

South Atlantic

East South Central

East North Central

Middle Atlantic

New England

West South Central

West North Central

Mountain

Pacific

0 5 10 15 20 25

19.4

20.1

19.5

18.3

19.2

18.6

18.0

19.0

18.3

There are only slight differences in average household VMT for the nine Census divisions.

Miles Traveled per Household (thousands)

Energy Information Administration/Household Vehicles Energy Consumption 1991 25
Source: Energy Information Administration, Office of Energy Markets and End Use, 1991 Residential Transportation Energy

Consumption Survey.

26 Energy Information Administration/Household Vehicles Energy Consumption 1991
The Effect of Vehicle Type

Minivans were driven more on average than any other type of household vehicle in 1991 (12,700 miles), followed

by sport-utility vehicles (11,800 miles), passenger cars (10,400 miles), large vans (9,800 miles), and pickup trucks

(9,400 miles).

Vehicle preferences reflect the household’s stage of life (singles with no children, households with young children,

households with teenagers or older parents, etc.). For example, households with children own 76 percent of the

minivans and 58 percent of the sport-utility vehicles (the two highest mileage categories). The presence of children

not only influences the preference for minivans and sport-utility vehicles but is also associated with higher VMT (as

discussed above).

Another reason for the relatively greater use of minivans and sport-utility vehicles is their relative newness in the

vehicle fleet. These alternatives to the more traditional station wagon or family sedan have only been on the market

since the last half of the 1980’s. They, therefore, have not had enough time to penetrate uniformly into older

households, and they are still too new to be relegated from their status of primary household vehicle. If these

vehicles were distributed more uniformly by age across the vehicle population, their usage would more likely

resemble usage patterns for other types of vehicles.

Insights from the Nationwide Personal Transportation Survey (NPTS)

Changes in demand for transportation by households, as detailed above, reflect the substantial changes in economic

and social factors over the past decade. The U.S. Department of Transportation’s Nationwide Personal Transportation

Survey (NPTS)3 provides some insights into these changes, which are not directly addressed in the RTECS itself.

In particular, the NPTS provides insights on the household demographics and economic changes responsible for

increases in the number of household trips and VMT.

In contrast to the RTECS’ focus on vehicles, the NPTS focuses on all types of trips--who makes trips in household

vehicles and why they chose household vehicles over other modes of transportation such as walking, biking or mass

transit. Despite the differences in what is measured by the NPTS and the RTECS, the coverage is similar enough

in the aggregate to justify using NPTS findings about travel behavior to explain the driving trends identified in the

RTECS. For instance, the NPTS estimates personal miles traveled (PMT) by any mode and examines the role of

personal vehicles in capturing an increasing fraction of PMT. The total VMT of 1,613 billion miles4 measured by

the NPT’s in 1990 is very similar to the 1,602 billion miles reported in the 1991 RTECS. The findings reported

below are based on the results of the 1983 and 1990 NPTS.

Growth in Personal Miles Traveled

Personal miles traveled increased by about 19 percent between 1983 and 1990. The NPTS attributes this increase

to three factors: population growth (4.3 percent), more trips per capita (7 percent), and longer trips on average (6.9

percent).

3

Travel Behavior Issues in the 90’s: Nationwide Personal Transportation Survey, U.S. Department of Transportation, Federal Highway

Administration, July 1992.

4

Includes travel-day and travel-period trips as explained in the box that follows on the NPTS.

Energy Information Administration/Household Vehicles Energy Consumption 1991 27
Although population growth is the smallest component explaining these changes, substantial regional shifts

in population can account for rapid growth in some areas - in particular the South and West Regions.

28 Energy Information Administration/Household Vehicles Energy Consumption 1991
The number of trips per capita represents the number of trips an average person undertakes for any reason,

by any mode of transportation. Women led the trend in the increasing number of trips per capita, largely

due to an increase in personal business trips. This trend is consistent with the increasing representation of

women in the work force since 1983.

The average trip length increased because of the increasing emphasis on travel to work. In particular, the

progressive shift of the population from urban centers to more suburban areas (and also out of the city)

increased the average length of the trip to work.

The Nationwide Personal Transportation Survey (NPTS)

The Department of Transportation’s NPTS used a random-digit-dialing telephone survey to interview

approximately 22,000 households about their driving patterns and estimated mileage. This information

supplements the RTECS information on vehicle consumption, mileage (both vehicle and personal), and

expenditures collected via two-stage personal interviews with over 3,000 households. RTECS data from

respondents’ odometer readings (more than 6,000 vehicles) are used to estimate the mileage traveled by the

vehicle-owning households nationwide.

In many respects, the two surveys complement each other and allow a better understanding of trends in

personal-travel behavior and energy consumption.

NPTS. The NPTS collects three types of information: (1) a "personal travel day" measure which

includes all trips for any reason over a 24-hour period, (2) a "travel period" measure which includes

long trips of over 75 miles one-way made in a 14-day period, and (3) a "commercial" travel measure

which includes travel by household members who drive as an essential part of their work. Surveys

are made throughout the year to account for seasonal variations. The NPTS covers all travel by any

mode of transportation including walking, bicycling, and motorcycles.

RTECS. The RTECS measures VMT using odometer readings taken at the beginning and end of the

year. This method captures all travel by household members in all vehicles that they either own or

use substantially.

Data Comparisons. The vehicle miles recorded for the RTECS include the vehicle mileage portions

of the "personal travel day" and the "travel period" measures reported in the NPTS, and some of the

"commercial" mileage. RTECS considers "commercial" travel as personal travel if the household has

access to that vehicle for personal use for more than a month of the year. RTECS, however, does not

include travel by walking, bicycling, and motorcycling, which are included in the NPTS.

Another trend noted in the NPTS is the substantial increase in the percentage of the population who drive,

particularly among women. Personal miles driven by women increased by 49 percent between 1983 and 1990 (91

percent for women in the 16-to-19-year-old range). Personal miles driven by men also increased, but by a more

modest 18 percent, mainly in the 16-to-34-year-old range. Men continue to account for approximately 70 percent

of the total personal miles driven.

Energy Information Administration/Household Vehicles Energy Consumption 1991 29
Growth in Vehicle Miles Traveled

Vehicle miles traveled are a result of: (1) the number of vehicle trips and (2) the average vehicle-trip length. The

increasing number of vehicle trips and vehicle miles of travel, as measured in the NPTS was much higher than would

be expected on the basis of the growth in personal trips and personal miles of travel. In addition to making more

frequent and longer trips, an increasing number of household members appear to be switching to using personal

vehicles for their trips and cutting back in their use of alternatives such as public transportation.

Although increasing trip length and frequency are the dominant forces behind the increase in VMT, other factors also

contribute to this trend. These include a decline in vehicle occupancy; a decline in use of public transportation and

walking as alternatives to vehicle travel; and increasing travel distances for commuting to work, for work-related

trips, and for trips to school and church (Figure 12). The following is based on the 1983 and 1990 NPTS.

The NPTS estimated that travel in personally operated vehicles increased from 82 percent of all travel in

1983 to 87 percent in 1990. This 5-percentage-point increase was accounted for by the increased number

of trips; the decline in the use of public transit and walking; and a net decline in those working at home

(due to a shift from rural to urban employment).

Average vehicle occupancy, a measure of the number of persons in a vehicle per vehicle trip, declined from

1.7 in 1983 to 1.6 in 1990. One factor contributing to this decline is the increase in working singles (male

and female) with vehicles. The decline in average vehicle occupancy means that 6 percent more trips were

required for the same set of riders to achieve the same person miles traveled5.

Average vehicle-trip length grew by 13.9 percent from 1983 to 1990. The family and personal business

grouping of trips for shopping, to doctors and dentists, and other family and personal business had the

largest increase in share of VMT. Social and recreational trips appeared to have declined as a fraction of

VMT.

Personal trip length grew by 9 percent. The average trip length for work and work-related business, and

school and church increased the most. Their fraction of VMT hardly changed over the 1983 to 1990

interval.

Household VMT, as recorded in RTECS, have grown for reasons more diverse than the simple compounding of the

growth of households and number of vehicles. These reasons include increases in the locational changes of

households and work, aging of the population, number of women holding driving licenses, and increases in vehicle

ownership. The aging of the population has led to more people in the 25- to 45-year old group, the years of peak

driving. Increase in female labor-force participation have led to more women holding driving licenses and more

driving for work, family, and personal business purposes. The locational changes of households and work have led

to longer trip lengths for work and work-related purposes. It could be argued that more and smaller households have

also led to fewer occupants in the average vehicle and more resulting trips. More recent Census-based data suggest

that some of these social and demographic measures may have slowed, perhaps to be overtaken by others.

5

100 average trips of 1 mile with 1.7 persons per vehicle is equivalent to 170 person miles. If the vehicle occupancy falls to 1.6,

then 170/1.6 trips are required for the same person miles: a 6-percent increase.

30 Energy Information Administration/Household Vehicles Energy Consumption 1991
Figure 12. Trends in Vehicle-Trip Length, 1983 and 1990

Sources: Department of Transportation, 1983 and 1990 Nationwide Personal Transportation Surveys.

Average Travel Day Trip

Other Social & Recreational

Visit Friends & Relatives

Other Personal Business

Doctor & Dentist

Civic, Educational & Religious

Shopping

Work Related

To Work

0 2 4 6 8 10 12 14 16

Trip Length in Miles

9.0

7.9

10.5

8.7

11.8

10.8

7.4

6.7

10.5

9.7

7.5

5.5

5.1

5.3

15.1

11.4

11.0

8.5

1983 

1990 

Average trip length for work, work related, school, and church trips increased substantially between the

1983 and 1990 NPT Surveys.

Energy Information Administration/Household Vehicles Energy Consumption 1991 31