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1 CHAPTER 1 INTRODUCTION This user's guide describes the recommended NCHRP Case 3a: Removal of Freeway HOV lane from an uncon- 25-21 methodology for predicting the long- and short-term gested freeway, mobile source emission impacts of traffic-flow improvement Case 3b: Removal of Freeway HOV lane from a con- USER'S GUIDE projects. The application of the methodology is illustrated gested freeway, through example problems consisting of case studies of var- Case 4: Narrowing a Street, ious traffic-flow improvements. Case 5: Access Management, Case 6: Intersection Channelization Improvement, Case 7: Signal Coordination, 1.1 OBJECTIVES OF THE Case 8: Transit Improvement, NCHRP 25-21 METHODOLOGY Case 9: Removal of a Freeway Express Bus Park-and- The objective of the NCHRP 25-21 research project was Ride Lot, and to develop and demonstrate, in case study applications, a Case 10: Construction of a 30-Year Transportation methodology to predict the short-term and long-term effects Improvement Program. of corridor-level, traffic-flow improvement projects on car- bon monoxide (CO), volatile organic compounds (VOCs), The case studies reported here in the user's guide are iden- oxides of nitrogen (NOX), and particulate emissions (PM). tical to the case studies described in the final report. Readers The methodology is designed to evaluate the magnitude, may note, however, that Case Studies 2, 3a, 3b, 4, and 9 here scale (such as regionwide, corridor, or local), and duration of involve the effects of removing lanes or a park-and-ride lot the effects for a variety of representative urbanized areas. It rather than those of adding lanes and a park-and-ride lot, as is designed to be implementable in a broad range of existing described in the final report. This is because it is mechani- software used for travel demand modeling. cally easier to remove an HOV lane or a park-and-ride lot The methodology is not designed to predict pollutant con- from coded highway and transit networks than it is to add centrations or ozone formation resulting from traffic-flow one. When adding facilities (such as an HOV lane or a park- improvement projects. Rather, the methodology uses the best and-ride lot) to a model, the modeler must also code the sup- available emission factors and vehicle operations and activ- porting link structure and must be careful to follow the net- ity data to estimate net changes in emissions of ozone pre- work coding conventions used in the network. When deleting cursors, CO, and particulates. a facility, the modeler need not be concerned about the cod- ing conventions. 1.2 ORGANIZATION OF USER'S GUIDE The user's guide consequently describes the case studies and their results as they were actually performed in the Puget Chapter 2 provides an overview of the NCHRP 25-21 meth- Sound Regional Council (PSRC) travel demand model. The odology. The next five chapters describe the various modules results from Case Studies 2, 3a, 3b, 4, and 9 were then reported of the methodology in more detail. in the final report as their mirror image. For example, a lane Chapters 8 through 19 illustrate the application of the meth- closure in the user's guide for Case Study 2 is reported as a odology to a series of case studies: lane addition in the final report. The "before" result for Case Study 2 in the user's guide became the "after" result in the Case 1: Addition of a Freeway Lane in a Rural Area, final report. The "after" result in the user's guide became the Case 2: Removal of a Freeway Lane in an Urban Area, "before" result in the final report.