Section 4

Consumer Vehicle 

Preferences
Energy Information Administration/Describing Current and

Potential Markets for Alternative-Fuel Vehicles 4-3

4.1. Introduction

The major aims of this study are to analyze and summarize the results of a national telephone survey of consumer vehicle

preferences and attitudes toward alternative-fuel vehicles. The study approach, the sample design specifications, the

questionnaire, and the processing specifications were developed by students enrolled in a survey practicum course at the

University of Maryland. This course is one of the graduate degree requirements of the Joint Program in Survey Methodology

sponsored by the University of Maryland, the University of Michigan, and Westat, Inc. The professor for the course, who

oversaw all aspects of the survey, was Dr. Stanley Presser. 

The eligible population for the study consisted of telephone households in the continental United States that owned or leased

one or more motor vehicles driven on a regular basis. The respondent was the adult in the household most knowledgeable

about the use of the household’s vehicle(s). Interviewing for the survey occurred from February 17 to May 16, 1994, in the

Maryland Survey Research Center (SRC) Telephone Facility on the College Park campus. The total number of respondents

was 1,712.

Highlights

The following are selected findings, estimated by analysis of the data obtained from the Consumer Preference Survey,

concerning the consumer population.

! Eighty-seven percent use personal vehicles as their main type of transportation

! Fifty-nine percent belong to households with two persons over the age of 18

! Eighty-five percent have heard of alternative-fuel vehicles

! Sixty-two percent feel that electricity is a safer vehicle fuel than gasoline

! Seventy-seven percent are concerned about outdoor air pollution in their area

! Sixty-one percent feel that vehicle emissions are extremely or very dangerous

! Forty-eight percent consider themselves to be environmentalists

! More than one-half are willing to refuel a vehicle twice as often as usual to reduce vehicle emissions

! About one-third are willing to reduce their current trunk or cargo space by one-half in order to reduce vehicle

emissions 

In order to understand much of the data presented in this report, it is necessary to understand the design of the questionnaire

and the way in which data were collected. The next section provides this essential information.

 

Design of the Questionnaire

The questionnaire opened with an eligibility question about the number of vehicles in the household. If the household owned

or leased one or more vehicles, a question was asked to identify the adult in the household who knew most about the

vehicle(s) and how they were used. If this adult was someone other than the initial informant, this person was contacted and

the number of vehicles was asked again.
Energy Information Administration/Describing Current and

4-4 Potential Markets for Alternative-Fuel Vehicles

Characteristics of Vehicles to be Replaced

73% were domestic vehicles

70% were automobiles

51% were bought used

38% were 1985-1989 models

32% were 1990-1994 models

70% of consumers were very/extremely satisfied with this vehicle

61% were used by someone in the household to commute to work

44% were used to make overnight trips

The remainder of the questionnaire fell into three broad categories: 1) vehicle questions, 2) vehicle preference questions,

and 3) questions concerning attitudes about pollution and the environment.

Vehicle Questions

For households with four or fewer vehicles, the main part of the

interview began with a series of questions about each vehicle

(year, make, model, whether bought new or used, and size and

usage of trunk (cargo) space), its regular uses (whether driven

to work, school, or as part of a job, and if so, how frequently

and how far), and its special uses (overnight trips or whether

it was entered into competitions). Questions were also asked

about fueling patterns and respondent general satisfaction with

the vehicle. These questions were, for the most part, asked in

order to select the vehicle that was to serve as the vehicle to be

replaced in the vehicle preference section of the questionnaire.

Consequently, analysis of these variables is not included in this

report. The survey assumed that the least used vehicle was the

vehicle with the highest likelihood of being replaced by a

modified vehicle. 

To reduce respondent burden, the very small number of households with more than four vehicles were asked only about the

two vehicles driven the least. This was done because in the vehicle preference section the respondent was asked to choose

between a modified vehicle and the vehicle in the household used the least. For households with multiple vehicles, the least

used was defined as the one least often fueled. If a tie occurred between two vehicles, it was broken according to which had

the least used trunk space, then according to which had the fewest overnight trips, and then by random selection.

Estimates for vehicle preference questions may include bias because of the sample’s design. Bias may have been introduced

in one of two ways. First, while the least-used household vehicle seems a plausible choice as the most likely vehicle to be

a candidate for replacement by a modified vehicle, no data are available to support this conclusion. The household vehicle

chosen for the vehicle preference questions might not have been the vehicle that the respondent would have chosen if given

the choice. Therefore, with respect to the vehicle population, the study cannot claim to represent preferences over the entire

stock, or even over the subset of vehicles most likely to be replaced by modified vehicles. The population that is covered

can be described most accurately as the subpopulation of least-used vehicles in U.S. households. Second, the respondent

may not have been the most appropriate person to make decisions about the vehicle addressed in the questionnaire. The

respondents were chosen on the basis of their knowledge of all the household vehicles, not on the basis of whether or not

they were directly responsible for the upkeep and operation of the least-used vehicle. Consequently, the respondent may not

have been the household member who was the main driver of the vehicle to be replaced or the member in the position to

make purchasing decisions regarding the vehicle. Likewise, the personal characteristics, opinions, and concerns for the

environment are those of the respondent and not the main driver of the vehicle to be replaced, except where otherwise stated.

This population would most closely represent the subpopulation of most vehicle-knowledgeable persons in U.S. households.

With these caveats in mind, some national estimates based on responses about households’ least-used vehicles are given

below. 
Energy Information Administration/Describing Current and

Potential Markets for Alternative-Fuel Vehicles 4-5

Vehicle Preference Questions

The respondent was asked a series of hypothetical choice questions between a new model of the household’s least-used

vehicle and a less-polluting modified vehicle that was identical to the regular vehicle except for certain limitations or

“penalty” characteristics. The limitations of the modified vehicle are similar to those currently associated with alternativefuel vehicles (AFV) and imply behavioral changes for the operator. The questionnaire contained three scenarios:

1. The modified vehicle has only one-half the trunk (cargo) space of the regular vehicle.

2. The respondent must drive 15 minutes out of the way to buy fuel for the modified vehicle.

3. The modified vehicle must be refueled twice as often as the regular vehicle.

Respondents were asked to choose which vehicle they would purchase, given each limitation individually and in combination.

Within each individual scenario, respondents who said they would choose the modified vehicle were asked which they would

choose if the modified vehicle cost $1,000 more than the regular vehicle. Respondents who chose the regular vehicle were

asked which they would choose if the modified vehicle was $1,000 less than the regular vehicle. Figure4.1.1 illustrates the

flow of the vehicle preference section of the questionnaire. In the figure, “M” means that the respondent chose the modified

vehicle. “R” means that they chose the regular vehicle.
Energy Information Administration/Describing Current and

4-6 Potential Markets for Alternative-Fuel Vehicles

Figure 4.1.1. Flow Chart of the Questionnaire

One-half Trunk/Cargo

Space

R M

15 Minutes Out of the Vehicle Vehicle

Way for Fuel Costs Costs Refuel Twice as Often

Modified Modified

$1,000 $1,000

Less More

RM M R

Modified Modified Modified Modified

Vehicle Vehicle One-half One-half Vehicle Vehicle

Costs Costs Trunk Trunk Costs Costs

$1,000 $1,000 (Cargo) (Cargo) $1,000 $1,000

Less More Space Space More Less

15 Minutes Out of the Way

for Fuel and Refuel Twice

as Often R

M Vehicle

Modified

Costs

$1,000

Less

15 Minutes Out of the Way

for Fuel, Refuel Twice as

Often and One-half

Trunk/Cargo Space

 Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program in Survey Methodology Consumer Vehicle

Preference Survey.

Additionally, for a random half-sample, the modified vehicle was described as producing half as much air pollution as a

regular vehicle; for the other half, the modified vehicle was described as producing no air pollution. Although the two

categories were general, the modified vehicle that produced no air pollution was intended to represent electric-powered

vehicles. The vehicle that produced half as much air pollution as a regular vehicle represented other alternative-fuel

vehicles, such as those powered by natural gas, propane, and other non-petroleum fuels. 

Attitudinal Questions

The final section of the questionnaire measured respondent awareness of AFV’s and attitudes about air pollution and

environmentalism. Questions included ascertained: (1) whether and to what extent respondents had heard of alternative-fuel

vehicles, (2) respondents’ perception of the relative safety of alternative fuels to gasoline, (3) respondents’ concerns about

air pollution in their area, and (4) whether and to what extent respondents considered themselves environmentalists.
Energy Information Administration/Describing Current and

Potential Markets for Alternative-Fuel Vehicles 4-7

Organization of this Report

 Sections 4.2 and 4.3 address three general topics: (1) consumer characteristics and their general attitudes and concerns

about air pollution, (2) prospective vehicle purchasers’ receptiveness to behavioral changes they might have to make to

operate an alternative-fuel vehicle, and (3) price differentials between conventional vehicles and alternative-fuel vehicles

that consumers will accept in making purchasing decisions. The detailed tables for the survey are found in section 4.4.

Section 4.5 contains the relative standard errors for the estimates found throughout this section of the report. Data quality

and methodology issues are briefly discussed in section 4.6.
33

27

35

37

31

67

73

65

63

69

Total

Northeast

Midwest

South

West

Census Region

100 0 20 40 60 80 100 80 60 40 20 0

Less than $30,000 $30,000 or More

Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program 

in Survey Methodology Consumer Vehicle Preference Survey.

Percent

AAAA

AAAA AAAA AAAA AAAA

AAAA

AAAA

AAAA

AAAA

AAAA

AAAA

AAAA AAAA AAAA AAAA AAAA

AAAA

AAAA

AAAA

AAAA

AAAA

AAAA

AAAA

AAAA AAAA AAAA AAAA

AAAA

AAAA

AAAA

AAAA

AAAA

AAAA AAAA AAAA AAAA AAAAAAA

AAA

AAA

AAA

AAA

AAAA AAAA AAAA AAAA AAAAAAA

AAA

AAA

AAA

AAA

39 42 37 38 39

42 39 45 43 42

12 15 11 12 12

7 5 7 8 8

Total Northeast Midwest South West

Census Region

0

20

40

60

80

100

Percent

One Two Three AAA Four or More AAA

Note: Percents may not sum to 100 due to rounding.

Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program 

in Survey Methodology Consumer Vehicle Preference Survey.

Energy Information Administration/Describing Current and

Potential Markets for Alternative-Fuel Vehicles 4-9

Figure 4.2.1. Household Annual Income by Census

Region

Figure 4.2.2. Number of Vehicles by Census Region

4.2. Consumer Characteristics, Awareness,

and Concerns

The Consumer Preference Survey contained questions to learn respondent demographic characteristics, consumer knowledge

of alternative-fuel vehicles, perception of the relative safety of alternative fuels, and general concerns for the environment.

 

Consumer Characteristics

The Consumer Preference Survey found that 39

percent of the telephone household population has one

household vehicle, 42 percent has two, 12 percent has

three, and 7 percent has four or more. Sixty-seven

percent of the population has an average annual

household income of $30,000 or more. For these

households, nearly 75 percent owned two or more

vehicles. In contrast, 64 percent of households with

annual income of less than $30,000 owned only one

vehicle. 

Nineteen percent of the population lives in the

Northeast, 25 percent in the Midwest, 35 percent in

the South, and 21 percent in the West. Within each

Census Region the household annual income is

distributed as shown in Figure 4.2.1. The Northeast

has the highest percentage of people earning $30,000

or more annually, and the South has the highest

percentage of people who earn less than $30,000.

Most households have one or two vehicles (about 80

percent). The distribution of the number of vehicles is

shown in Figure 4.2.2.
26

49

15

9

63

28

5 3

39

42

12

7

One Two Three Four or More

Number of Vehicles

0

10

20

30

40

50

60

70

Percent

Annual Income

Total

Less Than $30,000

$30,000 or More

Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program 

in Survey Methodology Consumer Vehicle Preference Survey.

Energy Information Administration/Describing Current and

4-10 Potential Markets for Alternative-Fuel Vehicles

Figure 4.2.3. Household Annual Income by Number of 

Vehicles

Consumer Characteristics

87% used personal vehicles as their main type of transportation

67% had household income greater than $30,000

69% lived in single-family detached homes

86% had high school or college education

59% belonged to household with two persons over 18 years of age

85% were white

Consumer Awareness and Opinions

85% had heard of alternative-fuel vehicles

18% felt that natural gas was a safer vehicle fuel than gasoline

29% felt that gasoline was a safer vehicle fuel than natural gas

11% felt that propane was a safer vehicle fuel than gasoline

41% felt that gasoline was a safer vehicle fuel than propane

62% felt that electricity was a safer vehicle fuel than gasoline

12% felt that gasoline was a safer vehicle fuel than electricity 

The relationship between the number of vehicles and annual income in households is shown in Figure 4.2.3.

Other consumer characteristic estimates are given below.

Consumer Awareness

Most consumers (85 percent) had heard of alternative-fuel vehicles, although only slightly more than one-half of the

population knew more than “just a little” about them. By far, the perception of fuel safety of alternative fuels was strongest

for electricity, with 62 percent stating it was a safer vehicle fuel than gasoline. The following summarizes consumers’

awareness of alternative-fuel vehicles and opinions of the relative safety of alternative fuels. 
53

55

49

50

62

47

45

51

50

38

Total

Northeast

Midwest

South

West

Census Region

100 0 20 40 60 80 100 80 60 40 20 0

Extremely/Very Somewhat/Not at All

Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program 

in Survey Methodology Consumer Vehicle Preference Survey.

Percent

Energy Information Administration/Describing Current and

Potential Markets for Alternative-Fuel Vehicles 4-11

Figure 4.2.4. Level of Concern for the Environment by 

Census Region

Consumer Concern for Environment

77% were concerned about outdoor air pollution in their area

Of these, 53% were extremely/very concerned 

61% feel that vehicle emissions are extremely/very dangerous

48% consider themselves to be environmentalists 

Consumer Concern

Concern for the environment was greatest in the Northeast and West Census regions (Figure 4.2.4).

Overall, consumers are concerned about the environment and consider themselves environmentalists; however, of the 48

percent who consider themselves environmentalists, only 22 percent are members of any environmental organization. 
Energy Information Administration/Describing Current and

Potential Markets for Alternative-Fuel Vehicles 4-13

4.3. Consumer Receptiveness to Behavioral 

Changes and Price Differentials

Respondents were asked whether they would purchase a new model of the household’s least used vehicle, or a less-polluting

modified vehicle (AFV) identical to the regular vehicle except for certain limitations that might require respondents to

change their normal behavior associated with operating a vehicle. Three simple cases were first addressed: the modified

vehicle would have only half the trunk space of the regular vehicle; the modified vehicle would require refueling at a station

that was 15 minutes out of the way for the respondent; and, the modified vehicle would need to be refueled twice as often

as the regular vehicle. If the respondent answered that they would choose the modified vehicle with the single limitation

over the regular vehicle, then they were asked about their vehicle choice if the modified vehicle had any combination of these

same three limitations. Additionally, in all the single limitation scenarios, respondents were asked a question regarding the

price of the modified vehicle to learn if a $1,000 difference in price would influence the respondents’ original vehicle

preference. Respondents who had chosen the regular vehicle were asked their preference if the modified vehicle cost $1,000

less. Respondents who chose the modified vehicle were asked their preference if the modified vehicle cost $1,000 more.

Single Vehicle Limitations

The following table presents consumer vehicle preferences, expressed in percents, when given three possible modified

vehicle limitations.

Table 4.3.1. Overview of Vehicle Preference by Modified Vehicle Limitations, 1994

(Percent)

Modified Vehicle Pollutes Half as Much as

Regular Vehicle Modified Vehicle Does Not Pollute

Vehicle Limitation Vehicle Vehicle Vehicle Vehicle Know

Regular Modified Don’t Know Regular Modified Don’t

One-half Trunk (Cargo) 60 33 Q 55 35 Q

Space .................

15 Minutes Out of the Way

to Refuel .............. 55 41 Q 44 51 Q

Refuel Twice as Often . . . 42 54 Q 37 57 Q

 Q = Data withheld either because the Relative Standard Error (RSE) was greater than 50 percent or fewer than 10 households were

sampled.

 Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program in Survey Methodology Consumer Vehicle

Preference Survey.

Between the two options of giving up one-half of the trunk (cargo) space of a regular vehicle and having to refuel the

modified vehicle twice as often, consumers in both pollution level groups were clearly more willing to refuel more often.

Twenty-one percent more consumers were willing to refuel twice as often than were willing to give up trunk space when

the modified vehicle polluted half as much as a regular vehicle, 22 percent more if the modified vehicle did not pollute at

all. Not much can be said, however, concerning consumer willingness to drive 15 minutes out of the way to refuel in

comparison to the other two options. The differences were statistically insignificant. 

With one exception, within each limitation scenario, differences among the pollution level groups’ vehicle choice were

statistically insignificant. The exception occurred when the respondent had to drive 15 minutes out of the way to refuel the
Energy Information Administration/Describing Current and

4-14 Potential Markets for Alternative-Fuel Vehicles

modified vehicle. Eleven percent fewer respondents chose the regular vehicle if the modified vehicle did not pollute than

if it polluted half as much as a regular vehicle.

The following sections look at the behavioral changes and the effect of price differentials on vehicle choice associated with

each of the vehicle limitations.

Giving Up Trunk Space

Potential vehicle purchasers were most reluctant to give up half the amount of trunk (cargo) space of their current vehicle

even if it meant halving or eliminating the pollution produced in operating a vehicle. Vehicle choice was related to the size

of the trunk of the consumer’s current vehicle (Table 4.3.2). 

Table 4.3.2. Vehicle Preference Regarding Loss of One-Half Trunk Space, by Size of Current Vehicle

Trunk, 1994

(Percent)

Modified Vehicle Pollutes Half as Much as

Regular Vehicle Modified Vehicle Does Not Pollute

Trunk Size Vehicle Vehicle Know Vehicle Vehicle Know

Regular Modified Don’t Regular Modified Don’t

Large .............. 58 34 Q 48 40 Q

Medium ............ 65 Q Q 54 Q Q

Small .............. 44 51 Q Q 60 Q

No Trunk ........... 66 29 Q 71 Q Q

 Q = Data withheld either because the Relative Standard Error (RSE) was greater than 50 percent or fewer than 10 households were

sampled.

 Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program in Survey Methodology Consumer Vehicle

Preference Survey.

As expected, those who currently had large or medium-sized trunks were less willing to replace their vehicle with one with

only one-half the trunk space no matter how much pollution was reduced. This result suggests that a large trunk may have

been an important factor in the purchasing decision of their current vehicle, and it continued to be a deciding factor in the

selection of a new vehicle. Consumers whose current vehicles had small trunks were more likely to choose the modified

vehicle, perhaps because trunk space was not as important as other considerations in their vehicle-purchasing decision. 

A result that appears surprising is that the majority of respondents who reported that their current vehicle had no trunk at

all were unwilling to buy the modified vehicle. The explanation lies in the wording of the trunk size and preference

questions. The question concerning current vehicle trunk size was asked about the space contained in the trunk of the vehicle

alone, while the vehicle preference question included both trunk space and cargo space. Therefore, a respondent who

answered that the current vehicle had no trunk most often had a truck, van, station-wagon, or sport-utility vehicle; all have

cargo space but no trunk. In fact, about 70 percent of those who stated that their current vehicle had no trunk were referring

to one of these types of vehicles. Since these vehicles are often purchased for their hauling capacity, it makes sense that

reducing the cargo space by one-half would not be a compromise many would be willing to make. For those respondents

who were not referring to one of these types of vehicles (30 percent), it is feasible that they were referring to an automobile

with a hatchback or whose back seat was used for cargo rather than passengers. It could also be that the respondent simply

would not purchase another vehicle without a trunk or other cargo space again. 

Price Differential. In both price cases, trunk (cargo) space seemed more important to consumers than $1,000. Consumers

who were willing to give up trunk (cargo) space were not willing to pay $1,000 extra to do so. The question of how much

pollution was reduced had little impact (Table 4.3.3). Consumers who chose the regular vehicle originally were not swayed
41 39 40

43 41

51

56

45 45

61

Total Northeast Midwest South West

Census Region

0

10

20

30

40

50

60

70

Percent

Pollution Level

Half Pollution No Pollution

Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program 

in Survey Methodology Consumer Vehicle Preference Survey.

Energy Information Administration/Describing Current and

Potential Markets for Alternative-Fuel Vehicles 4-15

Figure 4.3.1. Consumers Willing to Drive 15 Minutes Out of 

the Way to Refuel by Census Region

to choose the modified vehicle by $1,000. The price reduction was little incentive to accept the reduction in trunk space for

most people (Table 4.3.3). 

Table 4.3.3. Vehicle Preference Incorporating Price Differential Based on Original Vehicle Choice, 1994

(Percent)

Modified Vehicle Pollutes Half as Much as

Regular Vehicle Modified Vehicle Does Not Pollute

Differential Cost of Regular Modified Don’t Regular Modified Don’t

Modified Vehicle Vehicle Vehicle Know Vehicle Vehicle Know

$1,000 More ............ 68 26 Q 69 27 Q

$1,000 Less ........... 88 Q Q 79 Q Q

 Q = Data withheld either because the Relative Standard Error (RSE) was greater than 50 percent or fewer than 10 households were

sampled.

 Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program in Survey Methodology Consumer Vehicle

Preference Survey.

Driving 15 Minutes Out of the Way to Refuel

Respondents were nearly equally divided about

whether they were willing to drive a short

distance out of their way for fuel in order to

drive a vehicle that pollutes less. Unlike giving

up trunk space, willingness to purchase the

modified vehicle did differ between the two

pollution levels of the modified vehicle. Fortyone percent of the group given the halfpolluting modified vehicle scenario and 51

percent of the non-polluting vehicle group were

willing to travel 15 minutes out of their way.

Consumers offered a vehicle that did not pollute

at all chose the modified vehicle at a higher rate

than those who were offered a vehicle that

polluted only half as much. This trend was

especially strong among respondents who live

in the West or the Northeast. Figure 4.3.1

illustrates the difference between the two

groups by Census region. 

Respondents’ willingness to drive 15 minutes out of the way to refuel did not appear to be affected by their usual frequency

of gas purchase (Table 4.3.4). 
Energy Information Administration/Describing Current and

4-16 Potential Markets for Alternative-Fuel Vehicles

Table 4.3.4. Willingness to Drive 15 Minutes Out of the Way to Refuel by Frequency of Usual Gas

Purchase, 1994

(Percent)

Modified Vehicle Pollutes Half as Much as

Regular Vehicle Modified Vehicle Does Not Pollute

Frequency of Gas Regular Modified Don’t Regular Modified Don’t

Purchase Vehicle Vehicle Know Vehicle Vehicle Know

Less than Once a 58 38 Q 45 51 Q

Week ..............

Once a Week ........ 53 43 Q 42 51 Q

More than Once a

Week .............. 52 46 Q 45 46 Q

 Q = Data withheld either because the Relative Standard Error (RSE) was greater than 50 percent or fewer than 10 households were

sampled.

 Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program in Survey Methodology Consumer Vehicle

Preference Survey.

Price Differential. Nearly one-third of respondents who chose the regular vehicle over the modified vehicle that has to be

driven 15 minutes out of the way to refuel said they would choose the modified vehicle if it cost $1,000 less. There was

practically no difference among the pollution-reduction level groups (Table 4.3.5).

On the other hand, when those who originally chose the modified vehicle were asked if they would pay an additional $1,000

for the vehicle, over one-third said they would not. A larger percentage of potential consumers was “lost” because of a price

increase than was “gained” from a price decrease (Table 4.3.5).

Table 4.3.5. Vehicle Preference Incorporating Price Differential Based on Original Vehicle Choice, 1994

(Percent)

Modified Vehicle Pollutes Half as Much as

Regular Vehicle Modified Vehicle Does Not Pollute

Differential Cost of Regular Modified Don’t Regular Modified Don’t

Modified Vehicle Vehicle Vehicle Know Vehicle Vehicle Know

$1,000 More ............ 40 54 Q 33 61 Q

$1,000 Less ........... 68 29 Q 68 26 Q

 Q = Data withheld either because the Relative Standard Error (RSE) was greater than 50 percent or fewer than 10 households were

sampled.

 Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program in Survey Methodology Consumer Vehicle

Preference Survey.

Refueling Twice as Often

Of the limitations specified in this study for the modified vehicle, the one that respondents seemed most willing to accept

in order to reduce the amount of pollution emitted was refueling twice as often. More than half chose the modified vehicle,

54 percent among those offered a vehicle polluting half as much, and 57 percent among those offered the choice of a

nonpolluting vehicle. Frequency of regular fuel purchases affected willingness to purchase the modified vehicle only

minimally (Table 4.3.6). In the non-polluting modified vehicle cases, people who fueled once a week or more were more

willing to refuel twice as often than those who refueled less than once a week.
Energy Information Administration/Describing Current and

Potential Markets for Alternative-Fuel Vehicles 4-17

Table 4.3.6. Willingness Refuel Twice as Often by Frequency of Usual Gas Purchase, 1994

(Percent)

Modified Vehicle Pollutes Half as Much as

Regular Vehicle Modified Vehicle Does Not Pollute

Frequency of Gas Regular Modified Don’t Regular Modified Don’t

Purchase Vehicle Vehicle Know Vehicle Vehicle Know

Less than Once a 40 55 Q 39 53 Q

Week ..............

Once a Week ........ 41 54 Q 33 61 Q

More than Once a

Week .............. 47 52 Q 40 56 Q

 Q = Data withheld either because the Relative Standard Error (RSE) was greater than 50 percent or fewer than 10 households were

sampled.

 Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program in Survey Methodology Consumer Vehicle

Preference Survey.

Price Differential. The price differential affected the original purchasing decision in much the same way as it affected the

scenario requiring drivers to drive 15 minutes out of the way to refuel. The $1,000 price increase persuaded more people

to change their choice from the modified vehicle to the regular one than the $1,000 price decrease persuaded people to

choose the modified vehicle after choosing the regular one (Table 4.3.7 ). 

Table 4.3.7. Vehicle Preference Incorporating Price Differential Based on Original Vehicle Choice, 1994

(Percent)

Modified Vehicle Pollutes Half as Much as

Regular Vehicle Modified Vehicle Does Not Pollute

Differential Cost of Regular Modified Don’t Regular Modified Don’t

Modified Vehicle Vehicle Vehicle Know Vehicle Vehicle Know

$1,000 More ............ 37 56 Q 31 63 Q

$1,000 Less ........... 67 25 Q 72 22 Q

 Q = Data withheld either because the Relative Standard Error (RSE) was greater than 50 percent or fewer than 10 households were

sampled.

 Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program in Survey Methodology Consumer Vehicle

Preference Survey.

Combinations of Vehicle Limitations

Table 4.3.8 presents vehicle preference estimates given different combinations of vehicle limitations. Only those who

responded that they would choose the modified vehicle given the single limitation were asked about combinations of

limitations. Therefore, the populations these estimates represent are depleted populations of the total (Figure 4.1.1). 
Energy Information Administration/Describing Current and

4-18 Potential Markets for Alternative-Fuel Vehicles

Table 4.3.8. Overview of Vehicle Preference by Combinations of Modified Vehicle Limitations for

Depleted Populations, 1994

(Percent)

Modified Vehicle Pollutes Half as Much

as Regular Vehicle Modified Vehicle Does Not Pollute

Vehicle Limitation Vehicle Vehicle Know Vehicle Vehicle Know

Regular Modified Don’t Regular Modified Don’t

15 Minutes Out of the Way and

One-half Trunk (Cargo) Space 49 48 Q 52 45 Q

Refuel Twice as Often and Onehalf Trunk (Cargo) Space .... 51 47 Q 46 52 Q

15 Minutes Out of the Way and

Refuel Twice as Often ....... 24 75 Q 20 76 Q

15 Minutes Out of the Way,

Refuel Twice as Often and Onehalf Trunk (Cargo) Space .... 38 61 Q 34 62 Q

 Q = Data withheld either because the Relative Standard Error (RSE) was greater than 50 percent or fewer than 10 households were

sampled.

 Source: Energy Information Administration, Office of Energy Markets and End Use, Joint Program in Survey Methodology Consumer Vehicle

Preference Survey.

The addition of limited trunk or cargo space in the modified vehicle lost, by far, the largest proportion of consumers willing

to purchase a modified vehicle. How much pollution reduction the modified vehicle attained seemed to make little difference

in vehicle choice.

Consumers who were willing to drive 15 minutes out of the way and refuel twice as often individually, were usually willing

to do so in combination (75 percent and 76 percent). Of these, the addition of the loss of trunk (cargo) space lost a somewhat

smaller proportion of people willing to buy the modified vehicle than in the double combinations involving trunk (cargo)

space.

Conclusions

Overall, consumers seem fairly willing to accept vehicles with characteristics of alternative-fuel vehicles. The scenarios of

having to drive 15 minutes out of the way to fuel the modified vehicle and having to refuel the modified vehicle twice as often

gained wider acceptance than the scenario in which trunk (cargo) space was reduced. Perhaps, this suggests that particular

attention should be paid to solving the problem of limited trunk (cargo) space associated with those AFV’s that require a

great amount of space for fuel storage. There seemed to be a difference in vehicle preference when a price differential was

introduced. More respondents were dissuaded from purchasing the modified vehicle if it cost $1,000 more than were

persuaded to purchase the modified vehicle if it cost $1,000 less. For the most part, consumer preferences were not affected

by how much pollution was reduced. 
 Michael J. Brick and Joseph Waksberg, “Avoiding Sequential Sampling with Random Digit Dialing,” Survey Methodology (1991), pp. 17, 1

27-41.

 Joseph Waksberg, “Sampling Methods for Random Digit Dialing,“ Journal of the American Statistical Association (1978), pp. 73, 40-46. 2

Energy Information Administration/Describing Current and

Potential Markets for Alternative-Fuel Vehicles 4-87

4.6. Data Quality

Most of the information concerning the sample selection and sample weights found in the following pages is excerpted from

“Methods Report for Joint Program in Survey Methodology Study of Public Attitudes About Alternative Fuel Vehicles”

provided to EIA by the University of Maryland. 

Sample Selection

The eligible population for the study consisted of telephone households in the continental United States that owned or leased

one or more motor vehicles driven on a regular basis. The respondent was the adult in the household most knowledgeable

about the use of the household’s vehicles. 

The sample was selected using the Brick-Waksberg (1991) modification of the Mitofsky-Waksberg (Waksberg 1978) 1 2

Random Digit dialing two-stage cluster design. A frame of all possible clusters, defined as banks of 100 telephone numbers,

was generated (stratified by Census Region) from the January 1994 Bellcore Master Data File, a listing of all area code

exchange combinations in the United States. A systematic selection of clusters was then made from this frame. One

telephone number was randomly generated in each selected cluster and called. If it was a household, the cluster was retained;

if not, the cluster was excluded.

A total of 543 clusters was retained and eight telephone numbers sampled within each. Since clusters are selected with

probabilities proportionate to size and the number of second-stage households (households contained within the retained

clusters) can vary by cluster, the Brick-Waksberg design does not produce an equal probability sample. The design requires

weighting to adjust for these unequal probabilities.

Although the method does not achieve an equal probability sample, it has operational advantages. Unlike the MitofskyWaksberg design, the Brick-Waksberg method does not require sequential replacement of nonresidential telephone numbers.

Instead, the total sample is generated and released based on estimates of nonresidential telephone numbers and the

anticipated response rate. In this way, the cluster size is achieved without the cost of replacing non-households and

nonworking numbers as they are identified.

Response Rate

A total of 4,344 telephone numbers was selected from the 543 clusters. The disposition of these numbers is summarized

in Table 4.6.1.
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4-88 Potential Markets for Alternative-Fuel Vehicles

Table 4.6.1. Disposition of Selected Telephone Numbers

Phone Numbers Households Known Eligible

Non-households 1,638 Known Ineligible 219 Interviews 1,712

Never Answered 90 Unknown Eligibility 493 Refusals 111

Households 2,616 Known Eligible 1,904 Not-at-homes 60

Total 4,344 Total 2,616 Misc. Problems 21 a

Total 1,904

 Language, illness, or hearing problems. a

Of the 4,344 numbers, 1,638 were non-households (businesses and non-working numbers). In addition, 90 numbers were

never answered after at least 20 dialings and were assumed to be non-households.

Of the 2,616 identified households, eligibility (whether the household owned or leased a vehicle) was determined for 2,123,

of which 1,904 were eligible and 219 were ineligible. For 493 cases, eligibility could not be determined mainly because of

refusals. The response rate is the total number of interviews divided by the number of eligible cases. The unknown

eligibility category can be treated in various ways. The most conservative approach, treating 100 percent of such cases as

eligible, gives a response rate of 71.4 percent. A more realistic response rate can be calculated by assuming the same

proportion of these households had a vehicle (89.7 percent) as for the 2,123 households for which eligibility was determined.

This response rate is 73.0 percent.

Sample Weights

Two design weights were used to adjust for unequal probabilities of selection: (1) the inverse of the number of telephone

numbers in the household and (2) the ratio of the mean number of households per cluster to the number of households in the

particular cluster. (In eight cases, this weight was trimmed so that it did not exceed three times the mean weight.)

There are also two post-stratification weights: (1) a geographic weight to adjust the sample distribution by major Census

region to the distribution of all households with cars and (2) a cluster weight that is the ratio of households with cars (in the

cluster) to households with cars that meet the regular use screening criterion. (Most often, this weight equals 1.)

Finally, an additional factor sets the weighted sample size equal to the unweighted sample size. All weights and the

adjustment factor are combined into one variable (variable name = WEIGHT) and attached to the record for each case in

the data set.

Nonsampling and Sampling Error

The statistics in this report are estimates of population values. These estimates are based upon a randomly chosen subset

of the entire population of households with vehicles in the contiguous United States. As a result, estimates always differ

from the true population values. The differences between estimated values and the actual population values are of two

types, nonsampling errors and sampling errors. Nonsampling errors are errors of the survey process that can result from

difficulties such as unit nonresponse or item nonresponse, inaccuracies in data collection, or incomplete coverage in the

design of the sampling frame. Sampling error is a result of the survey design, due to the fact that data are obtained from

a subset of the population of interest, rather than all members.
DE×

PCT×(1&PCT)

n 'SPCT

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Potential Markets for Alternative-Fuel Vehicles 4-89

Nonsampling Errors / Adjustment for Item Nonresponse

Item nonresponse occurs when an item (or several items) is missing in an otherwise completed questionnaire, possibly

because the respondent does not know or, less frequently, refuses to give the answer to a particular question. Item

nonresponse is also recorded when the interviewer does not ask the question or does not record the answer during the

interview. For eight respondent demographic characteristics and 15 vehicle characteristic variables, values were imputed

for nonresponse. No imputations were made for missing preference or attitudinal items. Imputations were made using a

technique known as “hot-deck” imputation. In hot-decking, when a certain response is missing for a given respondent,

another respondent, called a “donor,” is randomly chosen to furnish its reported value for that missing item. That value is

then assigned to the respondent with item nonresponse.

To serve as a donor, the respondent has to be similar to the nonrespondent in characteristics correlated with the missing item.

This procedure was used to reduce the bias caused by different nonresponse rates for a particular item among different types

of respondents. Characteristics used to define “similar” depended on the nature of the item to be imputed. The most

frequently used characteristics were: Census region, State, age of the respondent, household income, type of home, and

education of the respondent. This analysis used a vector hot-deck procedure. With this procedure, the respondent that

donated a particular item to a receiver also donated certain related items if any of these were missing. Thus, a vector of

values, rather than a single value, is copied from the donor to the receiver. This helps to keep the hot-decked values

internally consistent, avoiding the generation of implausible combinations of respondent or vehicle characteristics.

Sampling Error

Sampling error occurs because the selected sample represents only one of the possible samples that could be selected under

the same survey specifications. The estimated values are developed from one of the many possible samples that could be

drawn and, therefore, will differ from true population values that would be obtained from a complete enumeration. Each

possible sample yields its own estimate of the true population values, with the differences attributable to the particular set

of cases selected in each sample. 

One measure of the variability of a survey estimate due to the sampling process is the average magnitude of the difference

between the values of the estimate for individual samples and the average value of the estimate over all samples of the same

size based on the same design. In other words, sampling error is a measure of the variability of an estimate over all

comparable samples, one of which was drawn. The average magnitude of the sampling error is measured by the standard

error of an estimate. The standard error is the root-mean-square measure of average difference over all possible samples.

Most statistical packages assume simple random sampling. This study employed a more complex design. Therefore, in

estimating sampling errors, a method is needed to take account of the sample design and the use of weights. SUDAAN

(Survey Data Analysis) was used to compute the design effect (the ratio of the variance reflecting design complexities to the

variance of a simple random sample of the same size) on 21 variables (five demographic, six attitudinal, and ten behaviorial).

The design effect was estimated at 1.13. Standard errors were computed by multiplying the standard error associated with

a simple random sample design by the design effect as follows:

where DE is the design effect, PCT is the estimate (in the form of a percent of the total), and S is the standard error of the PCT

estimate. 

 In this report, standard errors were expressed as relative standard errors (RSE). The relative standard error (RSE) is the

standard error expressed as a percent of the estimate, that is, for an estimate PCT:
SPCT

PCT 'RSEPCT

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4-90 Potential Markets for Alternative-Fuel Vehicles

Calculating the Confidence Range

To calculate the 95-percent confidence range

(that range which covers the true value of the

estimate with 95 percent confidence): 

1. Multiply the standard error by 1.96

2. Subtract the result of Step 1 from the given

estimate to determine the bottom of the range

3. Add the result of Step 1 to the given estimate

to determine the top of the range.

Measuring Statistical Significance

To determine if the difference between any two estimates in this report are statistically

significant:

1. Calculate the standard error of each estimate

2. Square the standard error of each estimate

3. Add the two values from Step 2

4. Take the square root of the value in Step 3

5. Multiply the value in Step 4 by 1.96 

If the value in Step 5 is less than the difference in the estimates, the difference between

the estimates is statistically significant.

Estimates with RSE greater than 50 percent were withheld from the published tables due to their lack of precision. Estimates

were also withheld if the number of observations was less than 10.

Using the RSE. To determine the standard error for an estimate, multiply the RSE for the estimate, shown in the tables in

this appendix, by the estimate. The standard error can be used to construct confidence intervals and to perform hypothesis

tests by using standard statistical methods.