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28 The approach used to develop an improved estimation procedure and data-collection methodology consisted of the following 12 sequential steps: 1. Compile and review existing data, practices, research, technical papers and articles, and other information from published, Internet, and informal sources. One source was a survey conducted by ITE that asked respondents whether they had data from studies of MXD. 2. Call sources of data or authors of documents contain- ing information of interest to obtain more details about data, procedures, applications, and lessons learned. 3. Develop a summary of practice and available data. 4. Determine what gaps exist in the data quantifying internal capture as well as estimation procedures and data-collection methods; this also included assessing the strengths and weaknesses of the data and methods being employed. 5. Change emphasis to collecting new data. The intent was to analyze and synthesize a potentially improved estima- tion procedure from the available data. The researchers found that the reported data available from respondents to the ITE survey were almost all estimates of internal capture used in TISs or related types of studies: there were little ac- tual survey data available. As a result, the researchers, in conjunction with the NCHRP Project 8-51 Panel, decided to shift the emphasis from analyzing existing data to collect- ing new data to add to the usable existing data. 6. Develop a proposed land use classification system that could be used both in the long term with an expanded data- base and in the short term with an initial smaller database. The land use classification system should be reflective of current and anticipated development trends for MXDs. 7. Develop an improved estimation methodology for cal- culating internal capture for MXDs in a manner that would be usable for at least TIS, using the land use clas- sification system for structure. A key feature was that the input variables need to be known at the stage of develop- ment during which rezoning occurs. In some cases, pre- liminary TIAs may even precede zoning (e.g., platting or subdivision). The procedures needed to be readily usable by analysts in consulting firms or public agencies and need to rely upon information that would be almost cer- tainly available or very easily obtainable in all instances. 8. Develop a methodology for collecting internal capture data in a manner that could be accomplished at a wide variety of MXDs using proven data-collection methods and tools for a reasonable cost. 9. Conduct a pilot study to test and then refine the data col- lection tools and procedures. With the shift in priority mentioned in Step 5, a second pilot study was added. Sub- sequently, a separate sponsor agreed to fund a related study that provided a third pilot study site and the resulting data. 10. Add the pilot study data to the existing base of usable data and develop the computational factors needed to populate the estimation method and tools. 11. Conduct a validation test to determine how well the esti- mation procedure reproduced the external trips obtained in the surveys at pilot and other sites. 12. Recommend methodologies for both estimation of inter- nal capture and collection of internal capture data. The desire was to create an improved method that would produce the following outputs: 1. A.M. and P.M. peak-hour internal person trips by land use in origin-destination form; 2. A.M. and P.M. peak-hour percent internal capture (person trips); and 3. A.M. and P.M. peak-hour inbound, outbound, and total external trips (trips to and from the development being analyzed) by mode â Person trips, â Vehicle trips, â Transit trips, and â Non-motorized trips. C H A P T E R 2 Research Approach
29 A key decision made early in the process was to use an esti- mation method usable with base trip generation estimates from other sources (such as the ITE Trip Generation Hand- book [1, Ch. 7] or local data). This decision was reached for the following reasons: 1. Relieve the method to be developed in this project from largely having to duplicate what has been accomplished over several decades to assemble the ITE and other local trip generation rate databases, 2. Make available a procedure that could be applied to MXD person trip generation that has been developed from any source, 3. Enable users more flexibility in how they conduct the remainder of their analyses, and 4. Focus resources on examining internal capture relation- ships and developing an improved estimation method. A second important decision was to develop a method that could grow with the size of the internal trip capture database. The background review found that there were little data avail- able at the necessary level of detail. The researchers recognized the need to be able to work with a small database to develop the methodology, but also saw potential advantage to being able to make the method and tools more sophisticated as the database becomes larger. For example, land use classifications could initially be basic (e.g., residential), but later be split into separate classifications (e.g., single unit detached, townhouse, and multiple family). The project panel reviewed results and provided sugges- tions at several junctures, beginning with the initial work scope. There was interest in both studying and surveying different types of MXDs. In the end, current and projected development trends and the limited data narrowed what could be included. The results documented in this report are for what are essentially single developments (i.e., one master developer developing under a single master plan on contiguous sites). Most are on multiple urban blocks. Site sizes range from less than 10 to more than 300 acres. Some could be considered âpodâ developmentsâthat is, develop- ments with multiple uses that are adjacent to each other, but not truly mixed together. Others are more fully integrated with closer proximity of interacting uses. However, all of the developments meet the definitions and characteristics iden- tified in this project for MXDs (see Chapter 1 and Appen- dixes A and B).
