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Pages 43-57

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From page 43...
... 43 5.1 Introduction This chapter provides information regarding Step 5 of a reliability improvement program: diagnostic assessment. It first presents an overview of a few broad elements of reliability before presenting a discussion of the many internal and external factors that have an impact on reliability.
From page 44...
... 44 Minutes Matter: A Bus Transit Service Reliability Guidebook • Inconsistent Dwell Times at stops will also introduce variability into bus travel times, affecting punctuality. Dwell times are closely related to the number of customers boarding and alighting at a stop but are also affected by fare collection procedures, boarding and alighting policies, the level of crowding on the bus, and wheelchair and bicycle securement.
From page 45...
... Reliability Diagnostic Assessment 45 primarily under the control of the transit agency and can, therefore, be directly modified to enhance reliability. External factors are not under the direct control of the transit agency and, therefore, can only be mitigated by agency actions or only be directly affected by partnering with other organizations.
From page 46...
... 46 Minutes Matter: A Bus Transit Service Reliability Guidebook The probability of late arrivals has been found to increase as buses travel along their routes, and there is a trade-off between running times and reliability when scheduling buses. Adding slack time to a schedule helps to improve reliability but can lower operating speed, which can lead to other negative consequences.
From page 47...
... Reliability Diagnostic Assessment 47 5.3.2 External Factors External factors are those that are not under the direct control of transit agencies; they relate to concerns such as roadway infrastructure, unpredictable customer behavior, traffic congestion, and other random events. While transit agencies cannot themselves control external factors leading to unreliability, they need to understand, anticipate, and monitor these factors and adapt to them.
From page 48...
... 48 Minutes Matter: A Bus Transit Service Reliability Guidebook increased customer demand and activity often correspond to declining service reliability, due largely to increases and fluctuations in dwell times. Research has shown statistical correlations between customer load and headway variation [22]
From page 49...
... Reliability Diagnostic Assessment 49 Reliability Elements and Factors Internal/External Factor Category Non-Operation Operator availability Internal Staff Vehicle availability Internal Fleet Breakdowns Internal Fleet Early/Late Start Insufficient recovery time Internal Planning Operator restroom breaks Internal Staff Holds for late connections Internal Service Poor operational control Internal Staff Mechanical issue Internal Fleet Variable Travel Speed Insufficient/excess scheduled time Internal Planning Too few/too many time points Internal Planning Overly long route Internal Planning Lack of adherence to time points Internal Staff Operator skill/behavior Mixed Staff Delays merging into traffic from stops Mixed Traffic Incidents, special events, construction Mixed Temporal Traffic congestion External Traffic Signal delay External Traffic Weather External Temporal Variable Dwell Times Too many stops/poorly located stops Internal Planning Poor transfer connections Internal Planning Uneven loading due to variable headway Internal Service Demand in excess of capacity Internal Customer Variable passenger demand Mixed Temporal Fare payment delays Mixed Service Access for cyclists Mixed Customer Access for mobility impaired Mixed Customer Inconsistent Transfer Times Insufficient recovery time Internal Planning Poor schedule coordination Internal Planning Poor route connectivity Internal Planning Table 5.2. Relationship of reliability measures to elements of unreliability.
From page 50...
... 50 Minutes Matter: A Bus Transit Service Reliability Guidebook dependent on reliable fast service, it is important that the transit agency guarantee performance and address any route issues. While most of the case study agencies actively addressed unreliability in real time, none described a formal process for diagnosing specific causes of unreliability; rather situations were generally addressed in real time using enhanced supervision and applying operational strategies (such as inserting spare buses, holding buses, deadheading, and introducing short turns)
From page 51...
... Reliability Diagnostic Assessment 51 • Are operators able to meet scheduled time points? If all the scheduled buses and operators are in service, and all trips have left the route endpoint on time but reliability at downstream time points is still a problem, agencies should first look for internal causes within their control.
From page 52...
... 52 Minutes Matter: A Bus Transit Service Reliability Guidebook sick or vacation days, then the focus may need to be on strategies to lower that rate. If rates are acceptable, then the size or scheduling of the extra board may need adjustment.
From page 53...
... Reliability Diagnostic Assessment 53 While there are several different methods for determining how much time should be allocated to running time versus recovery time, agencies can adopt a simple rule of thumb that buses should arrive at the end of a route before their next scheduled departure time a specified percent of the time, with that percent based on their on-time performance standard for trip starting point departures. If that percentage is, say, 95 percent, then running time plus recovery time should be set at or above the 95th percentile running time.
From page 54...
... 54 Minutes Matter: A Bus Transit Service Reliability Guidebook 5.6.4 Scheduling Adjustments at Time Points Along the Route While many of the factors affecting on-time departures at the beginning of a route are internal factors, the factors affecting reliability at bus stops and time points along a route can be a mixture of internal and external factors that can be much more difficult to separate from each other. Thus, causes of unreliability may be a combination of factors, and effective ways of addressing them may involve a combination of treatments, some of which may require involvement from other agencies.
From page 55...
... Reliability Diagnostic Assessment 55 window, then there may be too few time points on the route, and adding time points might help operators stay closer to the schedule. The route may also be an overly long route that is difficult to manage reliably due to the cumulative effects of factors causing variations in running time.
From page 56...
... 56 Minutes Matter: A Bus Transit Service Reliability Guidebook Even if there is enough capacity on a route, variability caused by other factors can be made worse by the bunching of buses and the uneven loading that results. Reducing the time per passenger it takes for passengers to board will help speed up late, over-crowded buses.
From page 57...
... Reliability Diagnostic Assessment 57 deceleration, entry into the stop, waiting for passengers to move to the bus (for larger stops) , passenger service time (dwell or door-open time)

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