Modeling, Implementation, and Validation of Arterial Travel Time Reliability

PI: Lily Elefteriadou, Ph.D., University of Florida

Travel time reliability has been proposed as a new concept that would allow agencies to evaluate the performance of a facility beyond just the peak hour, and to consider operations over a longer period of time considering non-recurring events.  Furthermore, the concept of travel time reliability has been widely recognized as one of, if not the, most important performance measure to evaluate highway traveler perceptions. However, determining how to measure, quantify, predict, and report travel time reliability has proved to be elusive.  Previous research funded by FDOT on travel time reliability developed, implemented, and evaluated tools for estimating travel time reliability for freeways. These can predict travel time reliability along the entire freeway portion of the SIS as a function of various changes in the system, such as incident removal times, and work zone occurrences, as well as selected ITS programs and initiatives (such as the road rangers). Previous research has also developed a method for estimating travel time reliability for arterials.  This method has not been implemented to consider the SIS, nor has it been validated using field data.  Furthermore, existing tools do not consider travel time reliability along multilane highways, nor the complexities of estimating travel time reliability in a multimodal environment.  The objectives of this research are to a) implement the arterial travel time estimation models to consider the entire arterial portion of the SIS, and to b) evaluate, validate, and adjust as necessary, the existing travel time estimation models for arterials using field data.

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Estimation of Capacities on Florida Freeways

PI: Lily Elefteriadou, Ph.D., University of Florida

The Highway Capacity Manual is the publication used most often to estimate capacity.  The current published version of the HCM (2010) defines the capacity of a facility as “...the maximum sustainable hourly flow rate at which persons or vehicles reasonably can be expected to traverse a point or a uniform section of a lane or roadway during a given time period, under prevailing roadway, environmental, traffic, and control conditions.”  The HCM 2010 indicates that the capacity of a freeway varies with free-flow speed (FFS) and that under base conditions it ranges from 2,400 pc/h/ln (for FFS 70 or 75 mph) to 2,250 pc/h/ln (for FFS 55 mph.)  Similarly, the HCM 2010 indicates that the capacity of a multilane highway ranges from 2,200 pc/h/ln (for FFS 60 mph) to 1,900 (for FFS 45 mph).  These values represent national averages and the HCM 2010 indicates that any given location may have larger or smaller values.  Furthermore, recent research has shown that maximum freeway throughput may be different in undersaturated and oversaturated conditions, and that the difference may be in the order of a 10% drop in throughput after traffic flow breakdown.   The main objective of this research is to collect field data at several freeway locations in Florida in order to capture capacity flows, and to provide recommended capacity and the corresponding speed values before and after the initiation of oversaturation.  The research team will also attempt to identify suitable locations along multilane highways to conduct a similar analysis.  The data will be obtained through STEWARD or other sources at various types of bottlenecks including merge junctions, weaving segments, as well as geometric bottlenecks (lane drops) and at locations with varying lengths of acceleration/deceleration lanes.

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Comparison of Methods for Measuring Travel Time at Florida Freeways and Arterials

PI: Lily Elefteriadou, Ph.D., University of Florida

Recent national and state efforts associated with travel time reliability have focused on the prediction of travel time as well as the travel time distribution and various travel time reliability-related measures. Previous research funded by FDOT on travel time reliability developed, implemented, and evaluated tools for estimating travel time reliability for freeways and arterials. In order to validate these travel time estimates, various sources of data have been used, including STEWARD, a central data warehouse developed by the University of Florida, and BlueToad data.  A third source of data is from INRIX, a company which provides real-time or archived travel time data.  The main objective of this research is to collect field data along several freeways and arterials and to evaluate the three travel time measurement methods outlined above, as well as any others that are currently used in Florida.

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