' (\{\. :, . p ·~searr fl n n c ~; / / f uP , /!JI/ ( 7/J f ' l;b Southwest Corridor Study Alternatives Analysis []f A~1erna1•ues I I I I I I I I I I I I I I :~ '° Regional hnsportation Authority Development Planning Office Chicago, Illinois August , 1980 Southwest Corridor Study Alternatives Analysis DEMAND ESTIMATION METHODOLOGY FOR THE FINAL SCREENING OF ALTERNATIVES The preparation of this report has been financed in part through a grant from the U.S. Department of Transportation, Urban Mass Trans­ portation Administration, under the Urban Mass Transportation Act of 1964, as amended. Development Planning Office Regional Transportation Authority Chicago, Illinois August, 1980 Report written by: Thomas A. Weaver Division of Public Transportation Illinois Department of Transportation RTA Southwest Corridor Study Project Manager, 1978-1980 Barbara F. Sloan Senior Planner Regional Transportation Authority author of the computer program for the Southwest Corridor Study CONTENTS CHAPTER ONE: INTRODUCTION • Overview of the Final Screening 1-1 • Methodological Needs and Constraints 1-1 • Generation and Distribution 1-2 • Mode Choice and Assignment 1-2 • Other Trip Destinations 1-2 CHAPTER TWO: FORMULATION OF THE NETWORKS • Geographic Areas of Analysis 2-1 • Highway Network and Auto Cost 2-1 • Transit Network 2-2 • Calibration of the Transit Network 2-3 • Station Coordinates 2-3 • Access Links 2-3 • Line Haul Travel 2-4 • CBD Egress Times 2-5 • User Costs 2-6 • Minimum Path Algorithm 2-6 CHAPTER THREE: OTHER COMPONENTS OF THE METHODOLOGY • Trip Tables 3-1 • Trip Distribution 3-1 1 Total Number of Trips 3-1 • Mode Choice Model 3-2 • Multipath Transit Assignment 3-3 1 User Benefit 3-4 CHAPTER FOUR: ANALYSIS OF RESULTS • Network Sensitivity and the Theta Value 4-1 1 Objective #1: Line Volume Accuracy 4-1 1 Objective #2: Replication of Bus-Rail Competition 4-2 • Objective #3: Significant Differences Among Alternatives 4-3 1 Objective #4: Realistic Prediction for Non-minimum Paths 4-3 1 Conclusion 4-4 • Analysis of Line Volumes in the Base Network 4-4 • Rapid Transit and Bus 4-5 • Commuter Railroad 4-5 Appendix: Acknowledgments CHAPTER ONE: INTRODUCTION OVERVIEW OF THE FINAL SCREENING The Southwest Corridor Study is being performed by the Chicago Department of Public Works, the Regional Transportation Authority, the Chicago Transit Authority, the Chicago Area Transportation Study, and the Illinois Department of Transportation to determine the pre­ liminary transit system design that is best able to improve travel between the Southwest Side of Chicago and the central business district (CBD). Four conventional technologies have been examined: rapid transit, light rail, busway, and commuter railroad. The total number of alternatives examined--approximately 600--is based on the number of alternative paths from terminus to terminus that the new line could take. The purpose of the Final Screening phase of the study has been to pare down the number of alternatives to approximately ten. This reduction is essential for a thorough evaluation of the best alter­ natives. The criteria used in the Final Screening include the costs of construction and rolling stock, predicted demand for the new line, changes in overall transit ridership, user time savings, operating costs, and a wide variety of non-user impacts. The means by which demand (ridership) and.user benefit were estimated are the subject of this paper. The demand for travel to the CBD and the potential user time savings were computed by means of a program written in Fortran IV for use on an IBM 3033 computer. The program used a CBD-oriented transit network, 1975 and 1990 trip tables (as input), a mode choice model, and a multipath transit assignment method. Each of these components of the program will be described in detail in this paper. METHODOLOGICAL NEEDS AND CONSTRAINTS Due to the high priority placed on this study by all partici­ pating agencies, it was considered necessary to develop, test, and apply a transit network and model(s) to the Southwest Corridor as quickly as possible. These steps were successfully completed within a seven month period (March-October 1979). The analysis began with the program and model of the RTA's recent Study of New and Replacement Rail Transit Alternatives (SONARRTA). However, in spite of the time frame, several changes were desired in the generation-distribution-mode choice-assignment process; these are highlighted below. 1-2 Generation and Distribution In SONARRTA, the overall number of trips from all zones to the CBD is kept at a fixed number for a given forecast year. The study's simultaneous distribution-mode choice model allows that as accessi­ bility to the CBD improves for a given zone, its total number of trips will increase; however, the increase is deducted from other zones in order that the overall number of trips remain constant. This was viewed as undesirable for the testing of the Southwest Corridor alternatives. In the latter case, the important factors were considered to be travel time savings and usage of the new line in the short-term future; potentials for changes in land use and travel patterns were expected to be marginal and less predictable. Most importantly, however, the "deduction" phenomenon mentioned above was viewed as theoretically invalid in this case. For evaluating long-term travel impacts, the best approach would be for trip generation--and distribution to the CBD--to increase somewhat when a new transit line improves CBD accessibility. A second, and more short-term, approach would be to fix all zone­ to-CBD distributions. In this manner, improved accessibility could alter only mode choice--not generation or distribution--and the results would apply only to existing travel to the CBD. Since there was not enough time to develop, test, and apply new generation and distribution models, the second approach was used. Mode Choice and Assignment In order to use a fixed generation-distribution trip table, it was necessary to replace SONARRTA's simultaneous model with a mode choice one; fortunately, SONARRTA developed a mode choice model calibrated and successfully tested for the Chicago area. With only a moderate number of changes, SONARRTA's minimum path algorithm could be retained for use in this analysis, thereby saving consider­ able time. A multipath transit assignment proces~ was considered necessary as a replacement for the typical all-or-nothing approach, to better reflect actual behavior, improve the accuracy of the estimated station and line riderships, and replace SONARRTA's logit-type "sub-mode choice" model for bus and rapid trans it. It was correctly predicted that the selected multipath assignment could be made operational within a very short period of time, i.e., approximately one week. Other Trip Destinations From the network tests performed as discussed in Chapter 4, 1-3 it was concluded that the network method predicts CBD-bound trips with considerable accuracy. The demand for two other trip types, however, was not computed as part of this effort. As trips passing through the central area but destined elsewhere ("through trips") were assumed to be in proportion to CBD-bound demand, there was no need to add such trips to the totals in order to discern differ­ ences among competing alternatives. "Local demand" (trips using the system but not reaching the CBD), however, will vary from alter­ native to alternative. Due to a lack of the time necessary to calibrate and validate an appropriate local demand model, accessi­ bility measures developed by DPW were used as surrogates. CHAPTER TWO: FORMULATION OF THE NETWORKS GEOGRAPHIC AREAS OF ANALYSIS The Southwest Corridor Study focuses on the Archer Avenue­ Stevenson Expressway corridor in the City of Chicago. However, for purposes of estimating overall impacts, a much larger study area was defined, as bounded by Madison Street on the north, State Street on the east, lllth Street on the south, and the Cook-DuPage County Line on the west {see Exhibit 2-1). This area extends fifteen miles east­ west and thirteen miles north-south. 1 The central area of Chicago was defined to include both the 11 11 central business district ( Loop ) and adjacent areas. Its defined boundaries are Chicago Avenue on the north, Lake Michigan on the east, Roosevelt Road on the south, and Halsted Street on the west; the total land area is three square miles. For purposes of trip measurement, the study area was divided into 367 zones, excluding the central area. Most of the zones were either of square-mile of quarter-section in size; the latter were located in the area of principal interest. The central area was divided into twelve quarter-sections. Each zone was given a centroid location, which was coded by means of an electronic digitizer at the University of Illinois at Chicago Circle by UICC personnel. The centroid was placed in the center of each zone unless the land use patterns called for a different location. HIGHWAY NETWORK AND AUTO COST The highway network consists of a 367-by-12 matrix of auto travel times from each of the Southwest Side zones to the twelve CBD zones. These 11 highway 11 times are a product of the Urban Transportation Planning System network model for the Chicago region which is maintained and operated by CATS. The actual highway system on which the times are based is the base network which existed in 1970. These figures were then increased by a factor of ten percent to account for a more congested highway network in 1990. In validating the mode choice and assignment models, the 1975 base system was tested. It should be noted that in testing the 1975 network, the 10% congestion factor was excluded from the auto times in order to simulate a realistic situation.