Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
80 This report describes the research findings of project NCFRP Project 25, âFreight Trip Generation and Land Useâ (Jointly funded as NCHRP Project 08-80). The main objec- tive was to study the relations between FTG and land use â. . . to develop a handbook that provides improved FTG rates, or equivalent metrics, for different land use character- istics related to freight facilities and commercial operations to better inform state and local decision-making.â As part of the research, an in depth examination of the key concepts and modeling methodologies for FTG was conducted. In addi- tion, a set of establishment-level FTG models were estimated for a set of case studies. The research process led to the iden- tification of a number of premises considered to be central to the development of FTG models. The most important of these premises is the need to make a distinction between FTG, i.e., the generation of vehicle trips, and FG, i.e., the generation of the cargo that is trans- ported by the vehicle trips. Furthermore, FTG is the result of the logistic decisions concerning how best to transport the FG in terms of shipment size, frequency of deliver- ies, and the vehicle/mode used. In some cases, this allows carrier companies to increase the cargo transported (the FG) without proportionally increasing the corresponding FTG. As a result, FTG cannot be universally assumed to be proportional to business size because large establishments could receive larger amounts of cargo without concomitant increases in FTG. This calls into question standard practices that assume proportionality between FTG and business size variables. Another important premise is that the accuracy of FG/FTG analyses depends on a number of key factors: (1) the ade- quacy of the classification system used to group commercial establishments in a set of standardized classes; (2) the ability of the measure of business size used to capture the intensity of FG/FTG; (3) the validity of the statistical technique used to estimate the model; and, (4) the correctness of the aggrega- tion procedure used to estimate aggregate values. In terms of land use, the research reviewed different defi- nitions and found a variety of non-integrated applications and classification codes currently in use. These can be catego- rized into three groups: the ones using structure type or site descriptor (e.g., ITE Manual or Tax Assessorâs codes); those using industry sectors at the establishment level (e.g., SIC or NAICS); and those using land use planning designations (e.g., LBCS and NYCZR). However, there is no one single land use classification system appropriate for freight. Moreover, the analyses revealed a number of aspects of great relevance for modeling purposes: it is important to use land use classifica- tion systems that lead to internally homogeneous classes, in terms of the determinants and patterns of FG/FTG activity, and it is important to use, as predictors of FG/FTG, variables that correctly measure the intensity of FG/FTG activity. The premises and conjectures discussed herein were tested using cases studies. To this effect, the research used FG/FTG data from: receiver companies in Manhattan and Brooklyn; carrier companies in Northern New Jersey and New York; a furniture store chain in Midwestern States; and, supermarkets in the Puget Sound region and Manhattan. Using the data, the research compared the performance of FG/FTG models based on: (1) Industrial classification systems (i.e., SIC, and NAICS); (2) Land use classification systems (i.e., LBCS and NYCZR); (3) the statistical technique used (e.g., OLS, mul- tiple classification analyses); (4) the aggregation procedure used; and (5) the business size variable used as predictors of FG/FTG. The case studies confirmed the superiority of economic classification systems over standard land use clas- sification systems; revealed that using economic classifica- tion systems as the foundation for the estimation of FG/FTG models is significantly better than using standard land use classification systems such as the NYCZR, or land use classi- fication systems that can be applied nationally such as LBCS; indicated that MCA performed better than OLS models; and confirmed that proportionality between FTG and business size only happens in a minority of industry segments. It also C h a p t e r 8 Conclusions
81 revealed that in 51% of industry segments the FTG is con- stant as it does not depend on business size; in 31% of cases the FTG model is a function of a constant and a rate that multiplies the establishmentâs employment; and in the remainder 18% of cases the FTG model is proportional to employment and a constant FTG rate. In addition, the case studies suggest that the models estimated at the establish- ment level are transferable, though more testing is needed to reach solid conclusions, and that the NCFRP Project 25 mod- els outperform both the ITE, and some industry segments of the Quick Freight Response Manual (QFRM). Although the work completed has primarily focused on FTG, the findings just discussed have important significant implications for both freight transportation planning and traf- fic impact analyses. During the second phase of the NCFRP 25âwhich will use the CFSâthe research will focus on the estimation of FG models. Ultimately, the entire set of findings will be synthesized in a set of guidelines for FG/FTG modeling.