Structure of this chapter is based on Chapter 9 of the FHWA Travel Survey Manual
Material has been reviewed and updated by Frank Southworth; Rob Tardif; Zak Patterson; Chris Simek; and Stephanie McVey
Commercial vehicle
surveys are used to collect profiles of goods and commodity
movements, and truck and commercial vehicle characteristics, within
particular areas of study. Surveys of this type have been conducted
for several reasons, including for use in statewide, regional,
subarea, and local travel forecasting models, in goods movement
studies, in management systems (in particular, intermodal and
congestion management systems), as well as in international border
crossing freight movement studies.
At this point in
time, commercial vehicle surveys are not typically performed to
support most statewide and Metropolitan Planning Organization (MPO)
travel model forecasting efforts. In most cases, states and MPOs
estimate commercial and truck travel models outside of the formal
travel modeling process. Secondary data sources are often used as
post-processors to develop commercial/truck vehicle trip tables and
models. However, as the analysis of commercial vehicle travel becomes
more important in urban planning, the collection of commercial
vehicle survey data will become quite important, as well. Lau (1995) provides a comprehensive overview and analysis of the types, uses, methods, response rates, and comparisons of recently collected commercial vehicle data in metropolitan areas throughout the United States. It also describes the needs and requirements of commercial/truck data collected to support regional travel models as well as the MPO transportation planning and management system (pavement, bridge, etc.) process. See also Lawson and Stratham (2002).
A number of research reports discuss this topic of combining travel survey data with additional forms of non-intrusive, IT-based data collection (Skszek, 2001; TRB, 2003; Southworth 2004), including the use of GPS technology for vehcile tracking (see Battelle, 1999) and growing number of active and passive and other roadside, on-board the vehicle and wide area sensors, including developments under the US Federal Motor Carrier Safety Administration's CVISN program (http://cvisn.fmcsa.dot.gov/).
GPS seems particularly well suited for commercial vehicles. Since the
travel patterns of vehicles, rather than persons, are desired, the use
of a GPS device on the vehicle is more likely to be accepted by the
respondent. GPS also greatly reduces the burden on the respondent since
destinations would not have to be recorded. This could be a substantial
advantage for vehicles that make many stops per day. The use of RFID
technology to track cargo movements by truck, rail, water and air is
also now spreading across the freight movement industry (http://www.rfidjournal.com/).
Assembly of Background Information
Three types of background data are likely to be especially helpful to the survey team:
-
Available commodity survey data;
Data on the commercial vehicle population; and
-
Commercial vehicle flow data.
These data are discussed below.
Available Commodity Survey Data
Typically, secondary data sources are used to
model and forecast commercial vehicle travel patterns in lieu of
collecting new survey data. Although there are a number of sources of
data required to support commercial vehicle surveying efforts, there is
little information collected by others which can be used directly in
the development of truck/commercial travel models. Ideally, available
recent survey data should provide information on commercial vehicle
trips by origin and destination, vehicle type, commodity type, and
time-of-day.
Following
a sixteen year hiatus in federal freight activity data collection the
1993, 1997 and 2002 U.S. Commodity Flow Surveys (CFS) filled a large
gap in this U.S. freight data universe. Since 2005 this gap has been
further reduced by a merging of CFS data with many other federally
supported freight and trade (inmpors and exports) data sources, and
combined using a variety of data intergation and synthesis methods to
produce a more comprehensive picture of US freight activity for the
years 1998 and 2002. Termed the Freight Analysis Framework, or FAF,
this FHWA supported data and analysis program provides access to
commodity flow matrices broken down by major commodity and modal
classes.
At the local level, systematic surveys of truck
travel are generally unavailable. The closest to the type of
information desired by urban planners and travel modelers are usually
the trip logs maintained by many commercial vehicle operators such as
delivery services (United Parcel Service and Federal Express), the
United States Postal Service, and many on-site repair establishments.
Although these trip logs can be used to create limited commercial
vehicle trip tables, they are the property of the privately held
businesses/establishments, and are therefore difficult to obtain.
Potentially, an aspect of a survey team’s
commercial vehicle surveying effort could be to request the voluntary
provision of these commercial vehicle trip logs for a sample of local
establishments. In addition, survey teams could also obtain applicable
information from the CFS in order to supplement the primary data
collection efforts envisioned for the survey effort.
Data on the Commercial Vehicle Population
Two data sources have typically been used to
provide transportation planners and modelers with commercial vehicle
population information which can be sampled to obtain commercial
vehicle travel data:
Vehicle registration lists by vehicle type and
owner address are generally available to local planners and travel
modelers from Departments of Motor Vehicles (DMVs). The vehicle type
classifications from these lists may or may not meet the planners’
needs, depending on whether or not vehicle weight and type codes are
maintained in the files, and on whether or not licenses are
differentiated by vehicle type. There may also be problems in
identifying passenger vehicles, pickup trucks, and small delivery vans
used commercially. This source typically fails to match the population
of vehicles actually operating in the study area because commercial
vehicle ownership, garaging, and usage often involves two or more
locations, some of which may be outside of the study area and therefore
impossible to survey.
A second type of data source is an establishment
listing. Commercial establishment lists are available in many forms,
ranging from telephone listings to publicly maintained lists.
Typically, State Departments which administer unemployment and work
compensation insurance programs and proprietary databases for sale by private firms, such as Dun and Bradstreet, maintain these listings.
No source will provide perfect data for the survey
sampling frame. Potential problems involved with data obtained from
these lists include:
An additional difficulty in using lists of this
type is that they typically include many establishments which do not
operate commercial vehicles. This leads to low survey eligibility
rates, which, in turn, lead to increased data collection costs
and longer than estimated field periods. It
is for this reason that it can be useful to stratify
businesses/employers by SIC/NAICS code to target industries most likely
to operate commercial vehicles (See Section on Sampling below).
Commercial Vehicle Flow Data
Information on commercial vehicle flows is often
valuable for model validation. This information can also be used to
monitor commercial traffic into and out of major facilities such as
large warehouses, piggyback rail yards, and ports. When
state-of-the-art technology is available, classification counts based
on the number of axles and length per vehicle can be obtained
automatically at traffic count stations. More typically, planners and
modelers must rely on available short-term manual classification
counts, frequently collected as part of traffic operation and impact
studies. Fischer and Han (2001) review the use of these and other data
sources for creating a set of truck trip generation rates for use in
planning models.
9.2 Commercial Vehicle Survey Design
The most basic design decision for the commercial
vehicle survey team is the selection of the appropriate survey
population and unit of analysis. Commercial vehicle surveys can be
performed by sampling:
-
Commercial vehicle trips at certain geographic locations;
-
The commercial vehicles themselves; or
-
The establishments that commercial vehicles serve.
If the vehicle trip is chosen as the unit of
analysis, the commercial vehicle survey is a simple extension to the
vehicle intercept survey described in Chapter 7.0.
When the intercept method is insufficient for the
anticipated analyses, a general population survey is needed. Often, the
population chosen for analysis is the commercial vehicles registered in
the study area. In this type of survey, the survey team contacts the
owners of a sample of the vehicles, and requests them to provide
detailed travel information for the vehicle. Some larger truck fleets
have been equipped with GPS tracking devices that allow fleet managers
to locate trucks at any given moment. These systems can be used
effectively for gathering truck-specific travel data with little effort by respondents. A major advantage of
this approach is that registered vehicle data can usually be obtained
from local DMVs at little cost. The major disadvantage is that vehicle
registration lists do not typically match the commercial vehicle
population in an urban areas since many trucks not
registered in the areas will be garaged and operated within the area,
and conversely many commercial vehicles registered in the area will
typically operate elsewhere.
Because of the problem with using the registered
vehicle as the unit of analysis, many commercial vehicle surveys
concentrate instead on establishments (see Chapter 10). The
advantage of using employers as the population to be sampled is that
nearly all commercial vehicle activity in a region is associated with
employment, either of the shipment originator, receiver, vehicle
operator, or a combination of the three. Exceptions to this rule of
thumb include rare cases of deliveries to households from external
study area locations by operators also based outside of the study area.
The disadvantages of using employers include the following:
-
Many businesses have very limited connections with commercial vehicle trips;
-
Establishing a comprehensive population of employers is often difficult;
-
The costs Costs of contacting the number of employers necessary to obtain a specified vehicle sample size may be significant; and
-
Two-stage, or stratified sampling is required to account for the
varying number of commercial vehicles associated with employers of
different sizes and types.
The choice of the unit of analysis is likely to
depend mainly on the anticipated modeling needs, but also on the
schedule and resources available to implement the commercial vehicle
survey. A survey based on vehicle registrations can usually be
conducted less expensively. However, the primary benefit of a survey
based on employers will be that it more accurately represents the
entire commercial vehicle population in the particular study area.
General Fieldwork Approach
The fundamental design problem typically faced by
surveyors is how to obtain travel behavior information directly from
the truck/vehicle operators. In most cases, owners of private trucking
and commercial businesses are not willing participants in this type of
survey effort, especially if they are asked to provide operational
information about their particular business. Past commercial vehicle
surveys have shown that response rates may be increased by obtaining
the support of the local or state motor trucking association. These
organizations act as intermediaries between their
constituent organization and the government entity often sponsoring or
funding the survey effort and can be invaluable in promoting the
survey. (Hunt, Stefan and Brownlee, 2006)
In addition, the survey design must include a
convenient mechanism to obtain travel information directly from the
vehicle operator, which is not always evident. Therefore, creative
methods for obtaining important travel behavior from the appropriate
businesses must be built into the survey design process. Standard
design features for the commercial survey include the following steps:
-
Contact businesses to obtain approval for survey participation;
-
Identify survey method;
-
Develop data recording method; and
-
Develop survey expansion method.
Recent experience in Chicago, Phoenix, Alameda
County (California), and Houston has shown that the following
multi-step approach is necessary to conduct and administer a successful
commercial vehicle survey:
-
Contact Businesses – Initial contacts with business owners
or employers should be established by telephone. Supplemental contacts
should be made by mail and/or in person (particularly for operators of
large fleets) to recruit survey participants. Typically, the survey
mail-out instrument requests establishment, vehicle, and travel
behavior data (trip diary forms) for a single-travel day. Data
retrieval is usually conducted either by mailback or telephone contact.
Attempts to simplify this process to a mailout/mailback strategy
have been made in at least one recent truck survey (in Phoenix) which
was based on vehicle registration data. However, because the response
rates were so low in the pretest, the approach was revised to represent
the approach described above . Incentives (e.g. chance to win a prize for participation) can help to increase response rates.
Details and potential refinements of this general fieldwork
strategy are discussed in subsequent sections of this chapter. An
important issue to address during the survey design is the degree of
coordination between the commercial vehicle survey, workplace surveys,
and vehicle intercept surveys discussed in Chapters 10.0 and 7.0
respectively. For example, if an employer database is used as the
sampling frame, then the procedures used to design the workplace and
establishment survey should be combined with those documented below.
This will minimize the effort required for meeting data needs and
reduce the number of business/employer contacts that have to be made.
Similarly, specific truck movements may be well captured by vehicle
intercept surveys, reducing the data needs for the commercial vehicle
survey.
-
Data Recording Methods – Typically, the recruitment of businesses/employers to survey is conducted through obtaining
vehicle registrations or by contacting businesses directly by
telephone. Data retrieval and recording methods for each include the
following approaches:
-
Vehicle registration information is obtained through the
Department of Motor Vehicles. Recruitment of businesses for survey
participation are typically obtained through telephone contacts and the
use of CATI.
-
Retrieval of survey forms is handled by either providing envelopes
with return of address and postage or mailback postcard forms. Returned
surveys, using either method, are directly input into established
computer databases or by using telephone/CATI. CATI is used to directly
enter survey responses for several survey types discussed in this
manual.
-
Employer contacts and subsequent survey recruitment are typically
made by telephone and CATI. In some cases, personal contact is made by
sending out initial survey participation forms designed to obtain
business participation in the survey. Data entry and retrieval use
similar methods described above for the vehicle registration approach.
-
Survey Expansion Method – The survey expansion methods typically used for each approach described above are presented below. For the vehicle registration approach, the sample expansion method includes:
- Developing a vehicle factor based on the number of vehicle
registrations divided by the number of responses by weight
classification or truck type; and
- Developing a trip factor based on the total number of
trips per truck obtained from the trip diary forms (typically, each
vehicle operator is asked for detailed travel behavior information for
a limited number of trips, e.g., for a given period, day, or week).
The sample expansion method typically used for the employer contact approach includes:
-
Developing an establishment factor based on the number of
employers divided by the number of establishments participating in the
survey;
-
Developing a matrix based on employer size, business type (SIC
code), and/or geography (location) in order to define the establishment
factor identified above;
-
Developing a vehicle factor based on the number of vehicles used
by a given establishment divided by the number of employers surveyed
(this factor can be truck type-specific); and
-
Developing a trip factor using similar methods described above for the vehicle registration approach.
9.3 Organizing the Commercial Vehicle Survey
As specified above, the design of the commercial
vehicle survey typically considers the vehicle registration or employer
contact approach. If the employer contact approach is used, close
coordination with the development and implementation of the workplace
and establishment survey is desirable. Similar to the other survey
types identified in this manual, and once the businesses for surveying
have been identified, the following design issues must be determined:
-
What is the appropriate survey approach?
-
Should the surveys be conducted using telephone interviews or be self-administered?
-
What count data are needed for the survey and how can it be obtained?
-
Should incentives for participating in the survey be offered?
The fieldwork approach must be identified in the
beginning stages of the survey effort. General descriptions of the two
typically used approaches, vehicle registrations and employer contacts,
are discussed in detail in Section 9.2
Once this approach is identified, the survey design must be determined. The survey design
should consider either the initial telephone contact, mail-out, and
follow-up telephone contact/CATI approach or the mail-out,
self-administered questionnaire, and mail-back approach to obtain the
travel behavior information required for analysis and travel modeling.
Both designs have been used for surveys of this type, with the higher
response rates associated with the telephone
interviews. Similar to other survey types, telephone interviews are
typically conducted by specialized market research firms. The
procedures required for implementation of telephone surveys are
discussed in greater detail in Chapter 6.0.
The problematic issue associated with conducting
telephone interviews for this type of survey is to identify the
appropriate mechanism to directly contact the commercial vehicle
operators. As stated previously, this direct operator contact is
essential to ensure that the proper level of trip-making and travel
behavior data is obtained. Other potential contact persons at employers
and businesses include dispatchers and business owners that may be able
to answer specific travel behavior questions about their commercial vehicle fleet. Online alternatives to conducting surveys are also becoming more commonly used.
With the self-administered surveys, similar and
additional problematic issues must be addressed in order to meet the
needs of the survey. For example, a mechanism has to be identified to
distribute the survey material from the employer/owner to the
appropriate vehicle operators. This must be defined early on in the
survey design once the self-administered survey is selected. Typically,
the distribution of questionnaire forms is administered by the business
employers’ owner or fleet dispatcher. Additional issues include ways in
which completed survey forms are collected and specific vehicles are
identified as survey participants. The self-administered questionnaires
are sent directly to the surveyor either by the individual vehicle
operators surveyed or by the employer/owner who collects the completed
surveys from the individual vehicle operators. Similar to the workplace
and establishment surveys, better response rates occur when the
employer/owner is responsible for collecting completed questionnaires
from operators for mail-back. Recent commercial vehicle surveys have
shown that some level of personal assistance (in the form of an
establishment site visit before the assigned travel day) by a survey
firm representative to address any questions or concerns the recruited
establishement may have may help increase survey response rates. (Hunt,
Stefan and Brownlee, 2006)
The following primary and secondary traffic data
can be obtained to supplement the information obtained from the
commercial vehicle survey:
-
Truck classification counts by weight and activity at cordon and/or screenline locations;
-
Truck classification counts at area Truck Centers and Weigh Stations;
- U.S. Census Commodity Flow Survey;
-
Vehicle Trip Logs from surveyed businesses; and
-
Truck classification counts at permanent station locations on state routes and major highways.
Much of this information can be obtained by using
the traditional data collection methods designed for other types of
surveys and travel models. For example, the traffic data collected for
vehicle intercept surveys can also be used to identify commercial
vehicle trucks movements at specific count locations. These data can be
used to expand the results of the survey to meet the commercial vehicle demand currently
operating on the roadway network. The cordon and/or screenline
commercial vehicle data are typically collected at the same locations
established for highway network automobile and transit traffic. This
ensures consistency with other models developed within the regional
travel modeling system such as the development of automobile trip
tables by trip purpose using the traditional Four-Step modeling
approach.
9.4 Sampling
Sampling strategies are typically conducted in two
stages. The first stage involves the selection of the business/employer
sample from all the businesses within the study area. The second is the
selection of the commercial vehicles (classifications) to be sampled
within the businesses selected for surveying. The sampling techniques
used for the commercial vehicle surveys can be dependent on other
survey efforts taking place, especially the workplace and establishment
survey, which use similar methods to define the sample of
businesses/employers.
Vehicle registration approach. In order to
obtain a reasonable level of information on trips by heavy/large
commercial vehicle classifications, sampling should be stratified by
vehicle type. Typically, three to four categories are selected for
sampling based on weight or the number of axles for each vehicle.
Sampling rates are usually established to achieve an equal number of
responses by each vehicle type. category.
Within each category, vehicles selected for
contact should be ordered randomly, by registration number, for
example, to avoid geographical and other biases if all vehicles are not
contacted.
Employer contact approach. The techniques used to sample workplace and establishment surveys and the issues in
identifying the sample of employers are discussed in detail in
Chapter 10.0. If the commercial vehicle survey is being conducted
independently of the workplace and establishment surveys, then it may
be desirable to stratify businesses/employers by SIC code
and target the sample on industries most likely to operate trucks and
other commercial vehicles. Otherwise, many contacts will be
non-productive and inappropriate for surveying because of limited
commercial activity. Sampling of vehicles within the
businesses will be warranted for establishments with large commercial
fleets. This will more than likely be the case for light and medium
vehicles because heavy vehicle operators may be difficult to locate and
subsequently survey.
9.5 Drafting and Constructing the Commercial Vehicle Survey
Data Elements
Typically, planners
design commercial vehicle surveys to determine vehicle owner
information such as industry type, number of commercial vehicles, and
number of employees; vehicle information such as size, weight, and body
type; and information on vehicle usage for a typical travel day. For
each commercial trip made on the specified travel day, information to
be obtained is typically desired for origin and destination locations,
trip start and end times, odometer readings, land use and/or industry
type uses at the identified origin and destination locations, activity
at the stop locations (loading, unloading, meal stop, etc.), stop
location (on- or off-street), and vehicle contents (commodities) during
the trip.
The level of detail concerning vehicle contents
can vary from simply noting whether the vehicle is empty or loaded, to
a detailed commodity description and/or code. Information on the
commodities transported is not a necessary element for most urban
planning and travel modeling applications, but may be desired for
particular urban, regional or interregional goods movement studies.
Survey Instruments
Similar to other surveys described in this manual, the survey instrument should be constructed to elicit the appropriate commercial vehicle operator responses to obtain the required data for input into the
travel demand modeling process. This includes drafting the appropriate
questions and constructing the survey instrument to meet travel
modeling needs. The telephone and self-administered survey approaches
are typically constructed differently and require different
questionnaire designs.
The telephone interview questionnaires are
typically more detailed and focus on obtaining other information
besides travel behavior. For example, surveyors may obtain commodity
flow and other non-related travel behavioral data. Telephone interview
questionnaires are also designed to allow for quick interviewer
tallying of responses by using personal interview scripts and CATI
programs.
The self-administered surveys typically contain
fewer questions and are targeted for quick response time. The survey
questionnaires must also be clear and easy for respondents to fill out.
Generally, a series of instructions are provided directly on the
questionnaire form to assist vehicle operators with instructions on how
to respond to the questionnaire. Return address and postage are
required for a self-administered survey with a questionnaire mail-back option.
In addition, it is recommended that the survey team ask commercial vehicle operators to review, test and
comment on early drafts of the survey questionnaire and materials. This
step will ensure that common terminology is used and understood.
Survey questions that might appear on a commercial vehicle survey include:
-
Business/employer location and address;
-
If appropriate, the Truck Center/Weigh Station location where the survey was completed;
-
Ultimate trip origin and destination including state, city, and nearest intersection;
-
Interim trip origins and destinations specifying segments/previous
stop locations of the entire trip (related to long-haul operators);
-
Start and end times of the entire trip (including all trip segments);
-
Major routes used for travel on the highway network;
-
Frequency of trips using this particular route by day, week, and month;
-
Frequency of trips using alternative routes by day, week, and
month (including reason for using alternatives such as congestion,
time-of-day, etc.);
-
Truck classification type and size categories (heavy, medium, light, small commercial);
-
Commodity/good that is being transported as well as
characteristics of the goods (value, etc., including whether or not the
load is empty) ; and
-
If appropriate, locations for pickup and delivery of goods.
The survey instruments from several recent commercial vehicle survey efforts are shown in Figures 9.1 through 9.4.
9.6 Pretesting
As with any survey, pretesting should be carried
out prior to the full implementation and administration of the survey.
In the case of the self-administered survey, surveyors can rely on
surveys already carried out in other locations to reduce the need for
extensive pretesting. For telephone interview surveys, it is important
that the surveyor test the entire process to ensure each component of
the survey is feasible and obtains the appropriate level of information
required for analysis and travel modeling purposes.
In some cases, self-administered (mail-back)
survey pretesting can be administered on a small scale to persons
within your company/agency to identify inconsistencies and other issues
associated with the format and wording of the questionnaire. In
previous chapters of this manual, procedures and requirements for
pretesting are discussed in greater detail.
Insert Figure 9.1 - 1of4
Insert Figure 9.1 - 2 of4
Insert Figure 9.1 - 3of4
Insert Figure 9.1 - 4of4
Insert Figure 9.2 - 1of3
Insert Figure 9.2 - 2of3
Insert Figure 9.2 - 3of3
Insert Figure 9.3 - 1of4
Insert Figure 9.3 - 2of4
Insert Figure 9.3 - 3of4
Insert Figure 9.3 - 4of4
Insert Figure 9.4 - 1of2
Insert Figure 9.4 - 2of2
9.7 Training and Interviewing
Similar methods for survey training described in
other chapters of this manual can be used to train and brief the
surveyor (telephone interviewer) staff designated to conduct the
commercial vehicle survey in the field. For example, the training
methods described for the household travel survey can be used for the
telephone interview approach described in this chapter. In addition,
the training methods for the Roadside Handout Survey described
in Chapter 7.0 and the workplace and establishment surveys in
Chapter 10.0 are very similar to the self-administered (mail-back)
survey described in this chapter.
Interviewer and surveyor courtesy and
persuasiveness in getting cooperation from employers and owners is
essential to the successful completion of the commercial vehicle
survey. Identifying the ‘path’ from the initial business/employer
contact to the appropriate decision maker who will agree to participate
and permit the survey to continue is also essential. This ‘path’ also
provides the reliable link between the employer and vehicle operator.
In most cases, survey training is conducted prior
to the pretest and the implementation of the overall survey with all
participating surveyors and interviewers. The training session is
typically conducted several days before the scheduled pretest and
overall survey dates. Surveyors are briefed on the purpose and
procedures on how to conduct the survey. Items generally covered by
survey administrators include:
-
Project briefing describing the background and purpose of the survey and a description of survey assignments for all surveyors;
-
Demonstrations of the procedures of the survey administration
describing surveyor/interviewer responsibilities for distributing
questionnaires, survey schedules, etc.; and
-
Survey procedures checklist provided to the surveyors and/or
interviewers during the initial briefing session, including
authorization letters and background material.
In commercial vehicle surveys designed for
administration at Truck Center and Weigh Station locations, it is
important for the survey administrator to coordinate with the surveyors
to ensure that they have been distributed all of the necessary survey
materials required to successfully carry out the survey. These survey
materials may include:
The survey administrators must also provide
additional instructions to the surveyors about the distribution of
forms to dispatchers and employers, as appropriate. If the survey
questionnaires have serial numbers, surveyors will be able to track the
Truck Center/Weigh Station, and employer locations and times of survey
distribution.
Variations of interviewing procedures can be used
depending on the survey method selected and the sample of commercial
vehicles to be surveyed. Also, survey notices should be distributed
among businesses/ employers and Truck Centers/Weigh Stations according
to the survey method chosen.
9.8 Coding
Commercial vehicle survey coding is conducted
using similar procedures used for other surveys described in this
manual. Similar techniques are used to code both the self-administered
(mail-back) and telephone interview surveys. The survey questionnaires
are typically designed to be self-coding (except for the
origin-destination information), where each survey response can be
coded to correspond to its answer check box number. Data coding can
either be completed manually by the surveyors conducting the telephone
interviews, by CATI, or by vehicle operators completing the
self-administered survey.
Typically, as with other surveys, data are punched
into a numerical ASCII data block for a specified width and length as
determined by the number of questions/responses and sample size of the
survey. Individual survey questionnaire responses are typically given
an identification number to track the responses for each
business/employer and vehicle operator surveyed. Survey origins and
destinations must be geocoded to identify the geographic locations of
the commercial vehicle trips surveyed. Chapter 14.0 provides a detailed
discussion of survey geocoding techniques.
9.9 Cleaning and Editing
Similar data cleaning and editing techniques used
for other surveys described in this manual are also conducted for the
commercial vehicle survey. As stated in previous chapters, completed
questionnaires should be edited as soon after collection as possible to
ensure that the proper surveyor techniques have been used and the
appropriate information has been obtained. Range checks should be
conducted to identify any data inconsistencies that may occur in the
coding process and to verify the accuracy of the data. Clearly invalid
responses should be checked for and removed before data are analyzed. If
data are collected over the web, this work can be done in real-time and
survey appropriateness can be examined (and possibly changed) as soon
as data starts to come in.
Uploading ....