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28 CHAPTER 2 Research Approach The approach used to develop an improved estimation ment during which rezoning occurs. In some cases, pre- procedure and data-collection methodology consisted of the liminary TIAs may even precede zoning (e.g., platting or following 12 sequential steps: subdivision). The procedures needed to be readily usable by analysts in consulting firms or public agencies and 1. Compile and review existing data, practices, research, need to rely upon information that would be almost cer- technical papers and articles, and other information from tainly available or very easily obtainable in all instances. published, Internet, and informal sources. One source 8. Develop a methodology for collecting internal capture was a survey conducted by ITE that asked respondents data in a manner that could be accomplished at a wide whether they had data from studies of MXD. variety of MXDs using proven data-collection methods 2. Call sources of data or authors of documents contain- and tools for a reasonable cost. ing information of interest to obtain more details about 9. Conduct a pilot study to test and then refine the data col- data, procedures, applications, and lessons learned. lection tools and procedures. With the shift in priority 3. Develop a summary of practice and available data. mentioned in Step 5, a second pilot study was added. Sub- 4. Determine what gaps exist in the data quantifying sequently, a separate sponsor agreed to fund a related study internal capture as well as estimation procedures and that provided a third pilot study site and the resulting data. data-collection methods; this also included assessing the 10. Add the pilot study data to the existing base of usable strengths and weaknesses of the data and methods being data and develop the computational factors needed to employed. populate the estimation method and tools. 5. Change emphasis to collecting new data. The intent was 11. Conduct a validation test to determine how well the esti- to analyze and synthesize a potentially improved estima- mation procedure reproduced the external trips obtained tion procedure from the available data. The researchers in the surveys at pilot and other sites. found that the reported data available from respondents to 12. Recommend methodologies for both estimation of inter- the ITE survey were almost all estimates of internal capture nal capture and collection of internal capture data. used in TISs or related types of studies: there were little ac- tual survey data available. As a result, the researchers, in The desire was to create an improved method that would conjunction with the NCHRP Project 8-51 Panel, decided produce the following outputs: to shift the emphasis from analyzing existing data to collect- ing new data to add to the usable existing data. 1. A.M. and P.M. peak-hour internal person trips by land use 6. Develop a proposed land use classification system that in origin-destination form; could be used both in the long term with an expanded data- 2. A.M. and P.M. peak-hour percent internal capture (person base and in the short term with an initial smaller database. trips); and The land use classification system should be reflective of 3. A.M. and P.M. peak-hour inbound, outbound, and total current and anticipated development trends for MXDs. external trips (trips to and from the development being 7. Develop an improved estimation methodology for cal- analyzed) by mode culating internal capture for MXDs in a manner that Person trips, would be usable for at least TIS, using the land use clas- Vehicle trips, sification system for structure. A key feature was that the Transit trips, and input variables need to be known at the stage of develop- Non-motorized trips.

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29 A key decision made early in the process was to use an esti- the methodology, but also saw potential advantage to being mation method usable with base trip generation estimates able to make the method and tools more sophisticated as the from other sources (such as the ITE Trip Generation Hand- database becomes larger. For example, land use classifications book [1, Ch. 7] or local data). This decision was reached for could initially be basic (e.g., residential), but later be split into the following reasons: separate classifications (e.g., single unit detached, townhouse, and multiple family). 1. Relieve the method to be developed in this project from The project panel reviewed results and provided sugges- largely having to duplicate what has been accomplished tions at several junctures, beginning with the initial work over several decades to assemble the ITE and other local scope. There was interest in both studying and surveying trip generation rate databases, different types of MXDs. In the end, current and projected 2. Make available a procedure that could be applied to MXD development trends and the limited data narrowed what person trip generation that has been developed from any could be included. The results documented in this report source, are for what are essentially single developments (i.e., one 3. Enable users more flexibility in how they conduct the master developer developing under a single master plan on remainder of their analyses, and contiguous sites). Most are on multiple urban blocks. Site 4. Focus resources on examining internal capture relation- sizes range from less than 10 to more than 300 acres. Some ships and developing an improved estimation method. could be considered "pod" developments--that is, develop- ments with multiple uses that are adjacent to each other, but A second important decision was to develop a method that not truly mixed together. Others are more fully integrated could grow with the size of the internal trip capture database. with closer proximity of interacting uses. However, all of the The background review found that there were little data avail- developments meet the definitions and characteristics iden- able at the necessary level of detail. The researchers recognized tified in this project for MXDs (see Chapter 1 and Appen- the need to be able to work with a small database to develop dixes A and B).