This paper explores the use of archived data to calibrate volume delay functions (VDFs) and updates their input parameters (capacity and free-flow speed) for planning applications. The sensitivity analysis of speed to change in congestion level is performed to capture functional characteristics of VDFs in modeling specific facility types.
This research study examines the safety impacts of the existing operator hours of duty policies in the state of Florida. Thus, this study uses questionnaire surveys, incident data archived by transit agencies and bus driver schedules to determine the relationship between crash involvement and operator schedules. Factors of interest in this study are the influence of shift pattern (start and end time), schedule pattern (split or nonsplit schedule) and time spent on driving. The study revealed that, operators working split schedules are more susceptible to fatigue than those working straight schedules. The group of operators working split schedules indicated less time of sleep, long driving hours and early startinglate ending schedule patterns. These the characteristics of fatiguing work schedule. There is also a strong statistical significance (p-value<0.001) attached to the association between crash occurrence and fatigue condition (red, yellow or green), with red condition contributing significantly to the total crashes (56.48%). Suggestion is made for the transit agencies to establish fatigue countermeasures through the use of fatigue detective technologies and policies.
Although traffic signals are installed to reduce the overall number of collisions at intersections, certain types, in particular, rear-end collisions are increasing due to signalization. One dominant factor associated with rear-end crashes is the indecisiveness of the driver, especially in the dilemma zone. An advisory system to help the driver make the stop-or-pass decision would greatly improve intersection safety. This study proposes and evaluates an Advanced Stop Assist System (ASAS) at signalized intersections by using Vehicle-to-Infrastructure (V2I) communication. The proposed system utilizes communication data, received from roadside equipment, to provide approaching vehicles with vehicle-specific advisory speed messages to prevent vehicle hard-braking at a yellow or red signal. A simulation test bed was modeled using VISSIM, a microscopic simulation software, to evaluate the effectiveness of the proposed system. The results demonstrate that at full market penetration (100% saturation of vehicles equipped with on-board communication equipment), the proposed system reduces the number of hard-braking vehicles by nearly 50%. Sensitivity analyses of market penetration rates also show a degradation in safety conditions at penetration rates lower than 40%. The results suggest that a penetration rate of at least 60% is required for the proposed system to minimize rear-end collisions and improve safety at the signalized intersections.
This research explores the association between fatigue-induced crash risk, transit operator hours of service and fatigue management policies in the state of Florida. Data used in this study include incident data archived by transit agencies and bus driver schedules. The results show a decreasing trend of collision risks when drivers start their schedules late morning or afternoon compared with early morning. The effect of time on task shows increasing collision risk as drivers drive long hours without enough off duty periods.
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