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CHAPTER 4 Procedures and Measures for Further Research The items in this section could not be examined in this project and require further research. These items can be classified into the following three groups: 1. Items that were initially identified to be beyond the scope of the project; 2. Items included in the original project plan, but were not analyzed because of time and budgetary constraints; and 3. Other areas identified during the course of the project. These are shown in Table 1 and are discussed in the following sections. An overview is pro- vided of each item, together with a discussion of its relative importance. Recommendations are made about specific research areas that should be examined in the future. The items detailed in Section 4.1 were originally discussed in the interim report, but have been reproduced here for convenience. Items in Section 4.2 have also been extracted from the interim report, but have been modified and shortened in most cases. The information presented in Section 4.3 is based mainly on comments made by members of the research team. 4.1 Items Initially Identified as Beyond the Scope of this Project 4.1.1 D-11: GPS Surveys There is growing interest in the use of GPS devices to collect data on sub-samples of households in household travel surveys. GPS is capable of providing very precise information about the loca- tions to and from which people travel, the times of their travel, the routes used, and even the traf- fic conditions along the route of travel at the time of travel. At present, this is largely an experi- mental procedure although it is moving rapidly forward as a mainstream activity in household travel surveys. There are at least 20 ongoing surveys that have a GPS component in the United States at the time of this report. Clearly there is potential for defining standardized procedures and providing guidance on a num- ber of aspects of such surveys. This includes sample sizes and methods of drawing samples, geo- graphic and socio-demographic distribution of the sample, the number of days for which GPS data should be collected, minimum hardware specifications for the GPS devices, the use of incentives, methods for deployment of the devices, methods of return of the devices, etc. However, at this time, it is probably too early in the development of such surveys, and there is too little experience to define standardized procedures. Therefore, this is an area that should be considered as being currently out of scope, but necessary to add within the next 2 or 3 years. It also may require extensive field exper- imentation to develop good standardized procedures through comparative studies that clearly show which are the preferred methods. Also, as personal GPS devices (as opposed to in-vehicle GPS devices) become more practicable and available, the nature of the survey may change quite rapidly. 48