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SUMMARY Standardized Procedures for Personal Travel Surveys Introduction Over the past 40 years, many millions of dollars have been spent on collecting household or person-based data for transportation planning. For most metropolitan areas, the largest routine expenditure made from planning budgets is to conduct household or person travel surveys. In some cases, the metropolitan regions that commission travel surveys do not have staff with in-depth knowledge and experience in that field. As a result, some Metropolitan Planning Organizations (MPOs) are unable to make informed selections of consultants to perform surveys and are also unable to assess whether a useful product was obtained. Sub- sequent work in using the data often reveals serious flaws in the data that could have been avoided if there were either a sufficient availability of expertise at the MPOs or a set of clearly defined procedures that could be followed by an MPO in guiding the process, selecting con- sultants, and assessing the work that was done. Some consultants who undertake such work are also unaware of the difficulties involved in data collection and have a lack of knowledge and expertise in various aspects of collection and assessment of the data that are apparent neither to them nor to the MPOs that may select them. They, too, could benefit from a set of standardized procedures and measures that would aid them in determining the type of survey to undertake, the methods to be imple- mented, and the means to assess whether the survey was being executed satisfactorily. Metropolitan planning staffs generally believe that data collected in one region have little relevance to another region. While there is no doubt that there will be local issues that may make transfer of data difficult or inappropriate at times, the major reason for this perception is that because each household travel survey is usually sufficiently different in design and execution from any other survey, comparisons from region to region are completely ob- scured by differences in method and implementation. If consistent procedures were used in the collection of such data, many of the apparent differences between regions would dis- appear. In addition, there are often slight variations in question phrasing that are sufficient to introduce major barriers to comparing data; appropriate standardization could remove these barriers. This could also lead to a greater willingness of regions to borrow data from each other and, thus, reduce the overall necessity to expend so much on collection of new data. It would also help the recognition and capture of travel among regions and, of partic- ular importance, would enable the relating of local to national surveys. Report Purpose This report presents the results of a study of those aspects of personal transportation surveys that could potentially be standardized--resulting in improvements to the quality, 1
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2 Standardized Procedures for Personal Travel Surveys consistency, and accuracy of the resulting data. The report is aimed at those who undertake personal and household transportation surveys, those who commission them, those who interpret and use the results of such surveys, and those who conduct research into improv- ing methods for such surveys. The report is organized into two main parts--NCHRP Report 571, the printed report, and NCHRP Web-Only Document 93, the technical appendix. NCHRP Report 571 is organized as follows: · Chapter 1: introduction. · Chapter 2: recommendations for all parts of a personal or household travel survey that could be standardized or areas where guidelines can be put forward that would produce greater consistency. · Chapter 3: outline of recommendations on how to implement the results of this research and move it out into practice. · Chapter 4: outline of those areas that were considered by the research team or that arose during the research, but which could not be accomplished in this research project; these areas could add further standardized procedures and consistency guidelines to surveys in the future. · Chapter 5: sample template for a Request for Proposals to conduct a household travel survey, incorporating all of the recommendations of Chapter 2. · Glossary: terms used in surveys, sampling, and related areas, which should be helpful for those with less knowledge about surveys. The Technical Appendix contains detailed descriptions of the research that was undertaken to develop the recommendations in this report, including the results of extensive literature reviews undertaken early in the project. An extensive set of references is provided at the end of the Technical Appendix, which is available on the TRB website as NCHRP Web-Only Document 93 (http://trb.org/news/blurb_detail.asp?id=8858). Practitioners (both those who commission and those who undertake surveys of household and person travel) will find Chapters 2 and 5 to be of most use to them. The transportation profession at large should also find Chapter 3 to be useful in terms of how to move these standardized procedures into broad use in the profession. Researchers will find Chapter 4 and the Technical Appendix to be of particular value. Those who are relatively less well acquainted with travel surveys should find the Glossary to be of help in understanding the report and its Technical Appendix. Both Chapter 2 of this report and the Technical Appendix are organized according to the chronology of undertaking a household travel survey. Initially, each of these deals with design aspects of a survey (survey instruments and data collection procedures), then pilot surveys and pretests, followed by the actual implementation of the survey. Next, they deal with the coding of data, including aspects of geocoding, and the analysis and reporting of the data, including documentation and archiving. Finally, they deal with the assessment of survey quality. Chapter 2 and the Technical Appendix's Chapters 410 are organized in parallel, and each provides cross references to the other. Thus, if a reader is reviewing a section of Chapter 2 of this report and wishes to examine the research that led to the recommendations in Chapter 2, a reference to the appropriate section of the Technical Appendix is provided. Likewise, a reader reviewing the research that was undertaken in the Technical Appendix is provided a reference to the recommendations that were devel- oped and are reported in Chapter 2 of the report. To avoid unnecessary repetition of mate- rial, the recommended standardized procedures and guidelines have not been repeated in the Technical Appendix.
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Standardized Procedures for Personal Travel Surveys 3 Summary of Recommendations It is important to understand what we mean by standardized procedures. Standardized procedures represent procedures that, if practitioners voluntarily adopt, will improve the consistency of household travel surveys. In many cases, adoption of these standardized pro- cedures will also result in improvements to the quality of surveys and improve comparabil- ity between surveys. They will also improve the reliability of the data resulting from such surveys and increase the accuracy of what is measured. However, standardized procedures are also only guidance. It is not intended that they be followed slavishly, nor that they should stifle innovation and improvement in surveys. However, they may be extremely helpful to those who are less knowledgeable about surveys in improving their ability to do, manage, or contract for such surveys. These are not standards, which would imply requirements, certification, and similar attributes. While standards may be desirable, they cannot be instituted without a body that will continually update them, ensure that they are being followed, and certify organizations as meeting the standards. There would also be a requirement for ongoing funding of such an activity. The research studied 40 different aspects in designing, implementing, analyzing, reporting, and assessing household and personal travel surveys. In almost all of these 40 aspects, recom- mendations were developed on elements of the survey that could be standardized or guide- lines that could be put forth to assist in achieving consistency in survey practice. In the area of survey design, these include a minimum set of questions that all such surveys should include, with standardized categories for recording responses to many of those questions, and suggested standardized wordings for asking some of the questions. In the design of data collection procedures, the issues addressed cover the number and type of contacts that should be made with potential respondents; how to handle proxy reporting; how to define what is a complete household; how to replace sample losses result- ing from refusals, terminations, and ineligibility; how to handle item non-response and unit non-response; how to make the initial contact, providing incentives; and how to measure and reduce respondent burden. In the area of pilot surveys and pretests, the research covered the necessity of doing such surveys and the sample sizes required. In survey implementation, the report addresses the ethics of undertaking a survey of a human population, how to design mailing materials, how to handle respondent questions, how to handle various forms of call screening, and what to do when reaching an answering machine or receiving repeated requests for a call back. It also covers ways to minimize the incorrect reporting of no travel, how to record the time of day in the data, what time the diary day should begin and end, and how to create useful ID numbers. In the area of data coding, two aspects of geocoding are addressed: with what precision should data be geocoded and what level of geocoding should be performed. This section also deals with how to handle missing values, when zeroes should be used, and some other fun- damental aspects of assigning coding values; it also addresses how to code complex variables where different levels of detail may be required in different surveys but comparability is to be maintained. In discussing data analysis and expansion, the report addresses how to assess and mini- mize sample bias, how to weight and expand the data to the full population, what to do about imputing missing data, and how to archive the data and provide comprehensive documen- tation of the survey.
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4 Standardized Procedures for Personal Travel Surveys Finally, in the section on assessing survey quality, the thorny issue of how to calculate the response rate is dealt with, including how to consistently code the outcomes of the various contacts made to potential and actual respondents. This section also discusses transporta- tion measures of quality, such as trip rates and non-mobility rates, and also outlines a number of standard assessment procedures that are used broadly in surveys: coverage error, proxy reporting, validation statistics, data cleaning statistics, the number of missing values, and overall adherence to quality standards. It is probably true that no household travel survey has ever incorporated all of the rec- ommended standardized procedures and consistency guidelines outlined in this report. Unfortunately, it is also probably true that most household travel surveys have not incor- porated most of these recommendations. However, if many of these were to be incorporated in future surveys, considerable gains would be possible in the overall comparability and quality of transportation surveys. Future Research In the chapter on future research (Chapter 4), another 30 aspects of the design and conduct of household travel surveys are identified as having potential for standardized procedures or consistency guidelines. These include emerging areas such as global positioning system surveys, Internet or web-based surveys, and the collection of stated preference data. There were also 18 aspects that were identified in the early stages of this research, but which were not researched because of lack of time or resources. These include issues relating to the design of data collection procedures, survey execution, sampling, pilot surveys and pretests, and quality assessment. Finally, there are 11 areas of research that were only identified during the course of this research because there was not sufficient time or resources to undertake all of the research that was desired (i.e., these would be an expansion on areas that were addressed partially) or that arose as a result of the research undertaken. Sample Request for Proposals Template The sample request for proposals (RFPs) template offers a template that embodies all of the recommendations made in Chapter 2, requiring the contractor to follow the standardized pro- cedures and guidelines. Tables and specifications are taken from the text of Chapter 2 and embodied in the RFP document. Places where the document needs to have inserted items specific to the region seeking proposals for a household travel survey are clearly indicated.