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72 CHAPTER 6 Transit LOS Model 6.1 Model Development LOS E was set for a hypothetical, base transit service on an urban street. A mode choice model would then be used to The Transit Capacity and Quality of Service Manual compare the ridership for the actual transit service to that for (TCQSM) provides a family of LOS models for dealing with the hypothetical base case. An increase in ridership over the several dimensions of transit service at different levels of ge- hypothetical base case would be interpreted as an indication ographic aggregation. The TCQSM is oriented to the entire of a preference for the actual service over the base case. The service area, the entire route, or the bus stop. It was necessary actual service would be assigned a level of service superior to to extract a subset of these quality-of-service measures that E. Similarly, lesser ridership would be interpreted as an indi- were most appropriate for a single urban street. The urban cation of poorer quality of service and would be assigned a street is at a level of aggregation that is greater than the bus level of service inferior to E. stop level and incorporates multiple routes using the street, The application of mode choice models at the urban street but it covers just the portion of the routes that actually use the level was considered impractical, so mode choice models street. Thus a different geographic focus was necessary in the were replaced with elasticities derived from typical mode development of the Urban Street transit level of service choice models. The elasticities predict the percent increase in model. ridership as a function of percent change in the transit service Transit riders were surveyed on portions of routes using a characteristics. specific urban street to determine what factors most signifi- cantly influenced their perceived quality of service. It was quickly discovered that passengers were basing their LOS rat- Selection of Explanatory Variables for LOS ings on their entire trip experience up to that point and not The Phase 1 surveys asked passengers to rate their satisfac- just the portion of their trip on a specific urban street. In ad- tion with 17 specific aspects of their trip. A multiple linear re- dition, an on-board survey can survey only those that even- gression model was developed that related individual factor tually chose to ride transit; it cannot take into account the ratings to the overall satisfaction rating. The factors that opinions of those who chose not to ride that bus or selected a added significance to the model were different route. Consequently, the surveys were used to iden- tify the key factors influencing perceptions of quality of ser- · Close to home rating; vice, but LOS models were not fitted to the on-board survey · Close to destination rating; levels of service. · Frequency rating; An alternative source of data on traveler preferences was · Reliability rating; necessary to construct an urban street level of service model · Driver friendliness rating; for transit. The working hypothesis of the research team was · Seat availability rating; and that "people vote with their feet." When confronted with a · Travel time rating. choice, people will pick the service that gives them more of what they value, in our case, quality of service. Thus, standard Of these factors, "close to home" and "close to destination" models of transit mode choice were consulted to identify the relate to getting to the stop, "frequency" and "reliability" re- relationships between various service characteristics and the late to waiting at the stop, and "driver friendliness," "seat likely proportional increase in ridership. availability," and "travel time" relate to the ride on the bus.
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73 Other considerations also had to be taken into account Moving the stop farther from the intersection increases walk- during this factor selection process: ing distances for passengers arriving from three of the four di- rections at the intersection, which can be related to walking 1. The factors included in the model should be under the con- time. On the other hand, near-side/far-side stop location trol of either the transit operator or the roadway owner; trade-offs can be evaluated through changes in travel speed, 2. To the extent possible and warranted, the factors as a using methodologies found in the TCQSM. whole should reflect the influence of other modes on tran- A third potential surrogate, and the one recommended by sit quality of service; the project team, is pedestrian LOS. Pedestrian LOS relates to 3. The factors should be readily measurable in the field; the ease of access to and from destinations along the urban 4. The factors should reflect conditions existing within the street, the quality of pedestrian facilities serving the bus stop, urban street right-of-way; and and the difficulty of crossing the street. It will be a part of the 5. The factors should have a documented impact on some as- multimodal urban street LOS methodology; therefore, no ad- pect of customer satisfaction. ditional data collection will be required. It is a measure of the impact of another mode on the transit mode and can be Based on these criteria, "driver friendliness" was dropped impacted by roadway agency actions. In short, it meets all of from consideration. Although partially under the control of the criteria set out above. the transit operator, this factor can only be measured through The TCQSM provides an areawide measure, "service a customer satisfaction survey, which we felt made it imprac- coverage," that addresses the "close to home" and "close to tical to include. In addition, we are not aware of any research destination" factors. This measure accounts for land use pat- relating different levels of driver friendliness to some measur- terns, street connectivity, and street-crossing difficulty, at the able aspect of satisfaction (for example, increased ridership). cost of requiring more data than is desirable for an urban The factors "close to home" and "close to destination" gen- street analysis. erated considerable discussion among the project team. The four remaining candidate factors are travel time, re- Walking distance to the stop depends on a number of factors liability, seat availability, and frequency. All are impacted by beyond the urban street right-of-way, including land use pat- conditions on the urban street, or by transit or roadway terns, street connectivity, transit route structure, stop loca- agency actions. All are related to TCQSM measures, which tions, and sidewalk provision on connecting streets, which is important from a consistency standpoint. The first three would tend to suggest not including these factors. At the same factors can be related to travel time, which addresses a panel time, there are known relationships that describe how bus pa- request to consider travel speed in the transit LOS model. tronage declines the farther one has to walk to a stop. The key remaining question is: Do relationships exist One potential surrogate measure identified through initial between passenger satisfaction and different values of these statistical modeling is "number of stops per mile"--the more factors? stops per mile, the shorter the distance passengers may have The answer to this question appears to be "yes." Consid- to walk to get to a stop once they reach the street with transit erable research has been conducted on traveler ridership re- service. However, there are two potential difficulties with this sponses to changes in service frequency and travel time. measure. First, the more stops per mile, the slower the bus (Both TCRP Report 95: Traveler Response to System Changes, travel time. Travel time is already identified as a potential and the Victoria Transport Policy Institute's Online TDM factor, so adding stops per mile to the model would be Encyclopedia provide extensive summaries of the literature redundant. Second, long stop spacing may or may not be in- pertaining to ridership responses to transit system changes.) convenient to passengers, depending on how convenient the For example, as bus headways decrease from 60 minutes to stops are to where passengers actually want to go. Without 30 minutes, from 30 minutes to 15 minutes, and so on, rid- knowing something about adjacent land development pat- ership increases, although in an ever-decreasing proportion terns (which takes the analyst beyond the urban street right- to the amount of added service. All other things being equal, of-way), it is hard to make a judgment about the impact of the relative amount of ridership one would expect at a given stop spacing on customer access. headway, compared to a 60-minute headway, is reflective of Another potential surrogate measure would be the dis- the difference in customer satisfaction between the two tance of the bus stop from the nearest intersection. This is headways. something that may be influenced by the auto mode--for ex- There is comparatively little research on the impacts of re- ample, traffic engineers frequently do not want far-side bus liability and crowding on ridership. However, reliability can stops located adjacent to intersections, in situations where be converted to an "excess wait time"--the average addi- buses must stop in the travel lane, because of the potential tional amount of time one would wait for a bus as a result of for cars to stop behind the bus and block the intersection. non-uniform headways. The excess wait time can, in turn, be