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5 CHAPTER TWO LITERATURE REVIEW INTRODUCTION in Fares and Services (7) and Traveler Response to Trans- portation System Changes (8,9) served as key source docu- This chapter summarizes findings from a literature review ments for a generation of transit planners attempting to related to transit ridership forecasting. A TRIS search was quantify the impacts of various types of service and fare conducted to aid the review. In addition, a message was changes. posted on the Travel Model Improvement Program e-mail list (see http://tmip.tamu.edu/email_list for more informa- tion) describing the synthesis project and requesting assis- MORE RECENT STUDIES tance. Additional studies for inclusion in the literature review were suggested by several respondents. TCRP is sponsoring an update and expansion of the TCRP Report 95: Traveler Response to Transportation System OLDER STUDIES Changes. Interestingly, one finding is that whereas much of the detailed information regarding transit service changes is Groundbreaking work on transit ridership forecasting goes old, it is not out of date. Several chapters have been finished back more than 30 years, with considerable activity in the and are available on the TCRP website, with the entire hand- 1970s and 1980s. The Urban Mass Transportation Adminis- book scheduled for completion in 2006. The 19 chapters in tration sponsored several studies at specific transit agencies, the final handbook address the following subject areas (10): including the Greater Cleveland Regional Transit Authority in Ohio (1). Other researchers in the 1980s developed tech- Multimodal/intermodal facilities, niques to forecast route-level or system-level ridership, Transit facilities and services, either through regression models using some combination of Public transit operations, service levels, fares, population, population density, employ- Transportation pricing, ment, distance from the nearest stop, automobile ownership, Land use and nonmotorized travel, and gasoline price and supply, or through a modified four-step Transportation demand management. travel model (25). Each chapter summarizes traveler responses to the spe- A 1983 report summarized the use of route-level ridership cific type of change addressed, discusses underlying factors prediction techniques (6). The authors identified eight differ- contributing to the traveler response, provides related infor- ent types of transit changes (seven service-related plus a fare mation and impacts, and presents case studies and examples. change) that use ridership prediction techniques, and charac- The most relevant chapters for this synthesis, Chapter 9, terized four general techniques: "Transit Scheduling and Frequency," and Chapter, 10 "Bus Routing and Coverage," have been released. Professional judgment; Noncommittal or stated-preference surveys; Chapter 9, "Transit Scheduling and Frequency" (11), Cross-sectional models, ranging in sophistication from describes ridership response to changes in frequency in terms similar routes and rules of thumb to regression analy- of service elasticity, with an average elasticity of 0.5. (Elas- ses; and ticities are generally used to estimate short-term changes in Time-series models, including elasticity-based ap- ridership in response to fare or service changes.) Higher elas- proaches and trend analysis. ticities are seen in cases where initial service levels are low (e.g., one bus per hour) and among higher-income riders. The various techniques were ranked subjectively on a num- Recent examples show frequency elasticities grouping around ber of factors, but concluded that insufficient information either 1.0 or 0.3, with the higher elasticities seen in sub- was available to address accuracy and transferability. urban systems and the lower elasticities in urban systems. It was noted that service reliability, clock face schedules that are Two broader works that encompassed examples from easy to remember, the condition of the transit fleet, and timed throughout the United States and the world were published transfers affect the response of riders to frequency changes, and/or updated between 1977 and 1981. Impacts of Changes but are difficult to quantify.