National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

Research Note

U.S. Department

of Transportation

National Highway

Traffic Safety

Administration September 21, 1995

Revised Vehicle Miles of Travel for

Passenger Cars and Light Trucks, 1975 to 1993

Terry S.T. Shelton

Background

The Federal Highway Administration

(FHWA) historically has supplied

registered vehicle and vehicle miles of

travel (VMT) data for use with the

National Center for Statistics and Analysis

(NCSA) motor vehicle injury and fatality

data. Over the last several years, though,

the boom in light truck sales (especially

minivans and sport utility vehicles) did not

appear to be reflected in the FHWA

registered light truck numbers. When

FHWA’s figures for registered cars and

light trucks were compared with R.L. Polk

data for these vehicles, large variations

were found (See Table 1). The explanation

for the majority of the differences in the

two sources of registered vehicles was

different definitions for cars and light

trucks. FHWA classifies minivans and

utility vehicles as passenger cars, whereas

Polk and NHTSA classify these vehicles as

light trucks. Starting with the 1993 Traffic

Safety Facts Report, NCSA began using

Polk registered vehicle data for calculating

fatality and injury rates per registered

vehicle. Although Polk data were readily

available, some data manipulation was

required and a complete description of this

effort has been published in a NHTSA

technical report, Registered Passenger

Cars and Light Trucks (DOT HS 808

235).

Table 1: Percent Registered Passenger

Cars and Light Trucks, 1975 to 1993

Year

FHWA R.L. Polk

 Cars Light Cars Light

Trucks Trucks

1975 84% 16% 82% 18%

1976 83% 17% 81% 19%

1977 83% 17% 80% 20%

1978 82% 18% 79% 21%

1979 81% 19% 78% 22%

1980 81% 19% 78% 22%

1981 81% 19% 77% 23%

1982 81% 19% 77% 23%

1983 80% 20% 77% 23%

1984 80% 20% 76% 24%

1985 80% 20% 76% 24%

1986 80% 20% 75% 25%

1987 79% 21% 74% 26%

1988 79% 21% 73% 27%

1989 79% 21% 72% 28%

1990 79% 21% 71% 29%

1991 78% 22% 70% 30%

1992 78% 22% 69% 31%

1993 78% 22% 68% 32%
National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

Investigation of VMT

The discrepancies discovered in FHWA’s

registered car and light truck counts

precipitated a review of FHWA’s

classification of light vehicles (passenger

cars and light trucks) for VMT. The VMT

for light trucks appeared to follow the

FHWA’s registered light truck numbers

and not the Polk light truck numbers. 

FHWA’s VMT figures are derived from

traffic count and vehicle distribution

information provided annually by each

state. For a complete description of the

recommended collection procedures, refer

to the Traffic Monitoring Guide (FHWAPL-95-031). Due to collection and

reporting differences in the states,

passenger car VMT may or may not survey of households in the nation. The

include VMT for small vehicles in addition primary objective of the NPTS is to collect

to cars, such as compact pickups, small trip-based data on the nature and

utility vehicles, and minivans. The extent characteristics of personal travel. The

of the problem is not easily discernible. A NPTS estimates of vehicle miles traveled

method to distribute total light vehicle are based on the survey respondent’s

VMT to reflect NHTSA’s vehicle estimate of miles each household vehicle

classification was necessary. was driven during the previous year. 

Alternative Sources for VMT Data

Two data sources were considered for

distributing light vehicle VMT between

cars and light trucks. The first data source

considered was the Residential

Transportation Energy Consumption

Survey (RTECS), a national survey of

households conducted by the Energy

Information Administration of the

Department of Energy. The purpose of the

survey is to collect information on the use

of energy in residential vehicles in the

United States. To qualify as a residential

vehicle, the vehicle 

could be owned or used by household

members for personal transportation or the

vehicle could be a company vehicle that is

kept at home and available for household

members. For each vehicle in the sample,

the RTECS collects a beginning-of-year

and 

an end-of-year odometer reading. Average

miles traveled per year are calculated by

vehicle type, including car, pickup, utility,

minivan and standard van. RTECS data

were available for 1980, 1983, 1985, 1988,

and 1991. 

The other source of VMT data considered

was FHWA’s Nationwide Personal

Transportation Survey (NPTS), a telephone

Estimates are available for different vehicle

types, but the vehicle classifications used

by FHWA are followed. For example,

utility vehicles have been included with the

passenger cars. 

RTECS was chosen as the best available

source of miles traveled data to distribute

light vehicle VMT between cars and light

trucks. The primary reasons for this

selection were that odometer readings are

considered more reliable than a person’s

recollection of miles driven, and the

vehicle classifications in RTECS could be

made to resemble NHTSA’s vehicle

classifications.
National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

Revision Methodology

The goal was to redistribute total light

vehicle VMT from FHWA for all years 

that VMT and data from the Fatal Accident

Reporting System (FARS) are available--

1975 to 1993. The ratio of the average

annual miles per car and light truck were

obtained from RTECS for as many years as

possible:

1980 RTECS: Average miles per car is

8% higher than light truck average.

1983 RTECS: Average miles per car is

7% higher than light truck average.

1985 RTECS: Average miles per car is

4% higher than light truck average.

1988 RTECS: Average miles per car is

4% higher than light truck average.

1991 RTECS: Averages are the same.

Three separate average adjustment factors

were calculated for the 1975 to 1993 VMT

recalculations. These adjustment factors

were applied to the percentage of registered

cars and light trucks based on the total

number of registered cars and light trucks

from Polk with the result being a revised

percentage of VMT for cars and light

trucks of the total car and light truck VMT. 

The factors were:

For data from 1975 to 1984, a

7.5% adjustment factor was

applied.

For data from 1985 to 1990, a 4%

adjustment factor was applied. 

For data from 1991 to 1993, no

adjustment factor was applied.

The factors were applied to the Polk

registered vehicle percentages for cars and

light trucks as follows, where

PC = percentage of passenger cars based

on Polk registered cars and light

trucks, and

LT = percentage of light trucks based on

Polk registered cars and light

trucks.

For 1975 to 1984,

Revised VMT % for Cars =

(PC*1.075)/(PC * 1.075 + LT)

For 1985 to 1990,

Revised VMT % for Cars =

(PC*1.04)/(PC * 1.04 + LT)

For 1991 to 1993,

Revised VMT % for Cars = PC

For all years,

Revised VMT % for Light Trucks

= 

100% - Revised VMT % for Cars.

The VMT percentages before and after the

revisions are shown in Table 2. As

expected, the revised VMT figures mirror

the Polk registration data very closely (see

Table 1). 
National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

Table 2: Percent of VMT for Passenger

Cars and Light Trucks, Results 

 1975 to 1993

Year

FHWA Revised

 Cars Light Cars Light

Trucks Trucks

1975 84% 16% 83% 17%

1976 83% 17% 82% 18%

1977 82% 18% 81% 19%

1978 80% 20% 80% 20%

1979 79% 21% 79% 21%

1980 79% 21% 79% 21%

1981 79% 21% 78% 22%

1982 79% 21% 78% 22%

1983 79% 21% 78% 22%

1984 77% 23% 77% 23%

1985 77% 23% 76% 24%

1986 77% 23% 75% 25%

1987 77% 23% 75% 25%

1988 76% 24% 74% 26%

1989 76% 24% 73% 27%

1990 76% 24% 72% 28%

1991 76% 24% 70% 30%

1992 77% 23% 69% 31%

1993 77% 23% 68% 32%

These revised percentages were then

applied to the total car and light truck

VMT from FHWA. The revised VMT

figures and revised fatality rates are shown

in Tables 3 and 4 on the next page. 

The most dramatic changes in VMT and

fatality rates based on VMT are found in

the light truck figures, especially in recent

years. For example, in 1992 and 1993 the

revised VMT was over one-third higher

than what FHWA reported. The result of

this revision is a 26% decrease in the

fatality rate when compared to the fatality

rate based on FHWA VMT. Changes in

the VMT figures and rates for passenger

cars are less dramatic, but are sizeable in

the last few years. Car occupant fatality

rates for 1992 and 1993 increased by 11%

and 12%, respectively, compared to the

rates based on FHWA VMT. 

The revised VMT figures and rates will be

published starting with the 1994 Traffic

Safety Facts Report. Rates in this report

include vehicle involvement rates for cars

and light trucks and injury and fatality

rates for car and light truck occupants. 
National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

Table 3: Revised VMT and Occupant Table 4: Revised VMT and Occupant

Fatality Rates for Passenger Cars, Fatality Rates for Light Trucks,

1975 to 1993 1975 to 1993

Year VMT VMT Rate Year VMT VMT Rate

Revised FHWA Rate* VMT Revised FHWA Rate* VMT

Chang Occupant From Chang Occupant From

e From Fatality FHWA e From Fatality FHWA

Change Change

1975 1,030,376 -0% 2.52 0% 1975 204,274 2% 2.38 -2%

1976 1,070,667 -1% 2.44 1% 1976 233,382 3% 2.33 -3%

1977 1,102,726 -1% 2.43 1% 1977 257,108 3% 2.32 -3%

1978 1,136,459 -1% 2.48 1% 1978 289,463 4% 2.33 -3%

1979 1,111,705 -0% 2.50 0% 1979 293,840 1% 2.44 -1%

1980 1,107,056 -0% 2.48 0% 1980 295,475 2% 2.53 -2%

1981 1,120,126 -1% 2.38 1% 1981 307,044 4% 2.31 -3%

1982 1,149,375 -1% 2.03 1% 1982 323,022 6% 1.97 -5%

1983 1,190,076 -1% 1.93 1% 1983 335,590 2% 1.85 -2%

1984 1,224,812 -0% 1.93 0% 1984 358,106 0% 1.81 -0%

1985 1,245,837 -1% 1.86 1% 1985 387,800 4% 1.72 -4%

1986 1,274,668 -2% 1.96 2% 1986 415,593 7% 1.76 -6%

1987 1,326,907 -2% 1.89 2% 1987 443,872 7% 1.82 -6%

1988 1,381,270 -3% 1.87 3% 1988 487,450 11% 1.70 -10%

1989 1,411,131 -5% 1.78 5% 1989 520,977 15% 1.64 -13%

1990 1,424,615 -6% 1.69 6% 1990 554,661 19% 1.55 -16%

1991 1,410,934 -8% 1.59 9% 1991 595,619 26% 1.41 -21%

1992 1,436,449 -10% 1.49 11% 1992 642,583 34% 1.26 -26%

1993 1,445,592 -11% 1.49 12% 1993 675,581 36% 1.26 -26%

 *Per 100 million VMT *Per 100 million VMT

Summary 

Based on the methodology described in This method for revising VMT may not be

this note, total VMT for cars and light applicable in future years. FHWA and

trucks as reported by FHWA has been NHTSA are working together to improve

redistributed. This revision affects the the registered vehicle and VMT data that

fatality and injury rates based on VMT for are used by both agencies. As more data

these vehicle types back to 1975. No become available, such as data from the

changes have been made to VMT for any 1994 RTECS and 1995 NPTS, the revision

other vehicle types, such as large trucks method will be re-evaluated. Also, as

and motorcycles. Fatality and injury rates states continue to use more sophisticated

for all vehicle types combined will be traffic equipment, better VMT data will

based on total VMT from FHWA, which become available. 

has not been revised.