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17 CHAPTER 3 Literature Review This chapter reviews the recent published research into transportation system's level of service, a review of the exist- multimodal level of service. The literature review is grouped ing literature by Flannery et al. (2005)  found little re- by research into traveler perceptions of level of service for search that empirically investigates these links. Flannery et al. auto, transit, bicycle, and pedestrian, and research into mul- conclude that a comprehensive research approach is needed timodal level of service frameworks. to identify and prioritize the factors important to drivers fol- lowed by research that models and calibrates these factors. In a study comparing users' perceptions of urban street 3.1 Auto Driver Perceptions of LOS service quality, Flannery et al. (2004)  found that HCM Researchers have focused on auto driver perceptions of 2000 methods only predicted 35 percent of the variance in quality of service for urban streets, signalized intersections, mean driver ratings, suggesting LOS does not completely rep- and rural roads. Researchers have used field surveys (where resent driver assessments of facility performance. subjects are sent into the field to drive a fixed course) and Colman  sent 50 students to drive various arterial video laboratories and have laboratory interviews to identify streets and compare the HCM level of service (based on key factors affecting perceived LOS and to obtain LOS ratings speed) against their own perception of quality of service. The for different field conditions. student's perceived speed thresholds for urban street level of Level of service has been defined by researchers in various service tended to be 4% to 24% higher than the HCM speed ways. For example, LOS A may be defined as "excellent," thresholds. They expected better service for a given letter "best," or "very satisfied" depending on the researcher. Others grade than the HCM. have defined LOS in terms of hazards and conflicts (e.g., num- Seeking to identify the key factors that influence user per- ber of vehicle-to-vehicle and vehicle-to-pedestrian conflicts). ceptions of urban street LOS, Pecheux et al. (2004)  used Some have developed models that predict the average LOS an in-vehicle survey and interview approach to determine the rating, while others have developed models that predict the factors that affect drivers' perceptions of quality of service. percentage of responses for each LOS grade. They identified 40 factors that are relevant to these perceptions, Several researchers have noted that drivers do not perceive including roadway design, urban street operations, intersec- six levels of service. Some researchers have proposed as few as tion operations, signs and markings, maintenance, aesthetics, three levels of service, while one researcher suggested a shift and the behaviors of other road users. A study by Flannery et al. of the entire LOS spectrum by one level of service so as to (2005) provides support for this collection of important fac- combine LOS A and B and subdivide LOS F. tors. Flannery et al. had drivers rate video segments of travel on Some of the latest research incorporates "fuzzy logic" in urban streets and then select and rank from a list of 36 factors the translation of user perceptions into letter grade levels of the 3 factors that they considered to be most important to LOS. service. Mean driver ratings had statistically significant correlations with operational and design characteristics, and aesthetics, in- cluding the following variables: travel time, average travel Urban Street LOS speed, number of stops, delay, number of signals, lane width, While the HCM's focus on measuring delay, percent of the presence of trees, and quality of landscaping. time spent following, and average travel speed (to name a An FHWA-sponsored study of customer satisfaction (SAIC few) offers a conceptual link to how the user perceives the ) sought to determine what factors influence perceived