The main objective of NCHRP Project 08-80/NCFRP Project 25 was to study the relationship between freight trip generation (FTG) and land use and . . . to develop a handbook that provides improved freight trip generation rates, or equivalent metrics, for different land use characteristics related to freight facilities and commercial operations to better inform state and local decision-making. As part of that quest, the research: consolidated the available FTG models in an electronic database to assist practitioners interested in using these models; undertook an in depth examination of the key concepts to identify the most appropriate approaches to develop and apply FTG models; and, used data previously collected by the team to estimate establishment-level FTG models for a number of case studies. This process led to the identification of a number of premises considered to be central to the development of FTG models able to satisfy the needs of both transportation planning and traffic impact analyses. The most important of these premises is the need to make a distinction between FTG, i.e., the generation of vehicle trips, and freight generation (FG), i.e., the generation of the cargo that is transported by the vehicle trips. FG is an expression of economic activity performed at a business establishment by which input materials are processed and transformed generating an output that, in most cases, is transported elsewhere for further processing, storage, distribution, or consumption. FTG, on the other hand, is the result of the logistic decisions concerning how best to transport the FG in terms of shipment size, frequency of deliveries, and the vehicle/mode used. Of great importance is the shippers ability to change shipment size to minimize total logistic costs, as it allows shippers and carriers 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 has major implications for FTG modeling, as standard practices implicitly assume proportionality between FTG and business size variables (e.g., square footage, employment). Another important premise is that the accuracy of FG/FTG analyses depends on a number of key factors: (1) the adequacy 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 aggregation procedure used to estimate aggregate values (if required). In addition to these FG/FTG specific factors, other basic principles hold true: the better the quality of the data, the better the results; and, that disaggregate models (establishment level) are generally better than aggregate models (zonal level). In order to ensure proper understanding and use of the terms, brief descriptions are provided. A classification system is a systematic way to group individual entities into pre-defined groupings or classes with which they share common features.


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