FDOT Sponsored Research, BDK77-931-04 (Cost-share for STRIDE)
PI: Lily Elefteriadou, Ph.D.
[final report]
Abstract
Four previous FDOT research projects on travel time reliability (FDOT Contracts BD-545-48, BD-545-70, BD-545-75, and BDK-77-977-02) developed tools for predicting travel time reliability for freeways. These tools can provide travel time reliability as a function of various changes in the system, such as incident removal times and work zone occurrences, and were applied to estimate travel time reliability in Broward County, Florida.
The objectives of this research were to
(a) implement the procedures developed on the entire freeway portion of the SIS
(b) enhance the existing procedures to incorporate additional elements such as the impact of incidents on each freeway segment and the impacts of various ITS strategies
(c) validate the estimates obtained using field data for those portions of the SIS where travel time information is available
(d) establish procedures for updating the travel time reliability estimates on an annual basis
A series of recommendations were developed for incorporating the impacts of several ITS strategies into the travel time reliability analysis. However, the literature is sparse relative to the operational impacts of these strategies, thus, the recommendations developed should be used with caution, and they should be updated when additional evaluation studies become available. The methodology was enhanced by considering weather-related impacts on travel time. Weather impacts focus on rain intensity. Visibility impacts were also evaluated, however it was recommended not to include these at this time. The calculation fora non-blocking incident frequencies was re-evaluated and new recommendations were developed and implemented in the database. These revisions provide more reasonable results in the frequencies of non-blocking incidents. Travel time reliability results were provided for the entire portion of the SIS for the year 2007. The results are reasonable, however there are some discrepancies observed between field data and estimated values. It is likely that either the congested travel times are underestimated, or that the frequency of the congested scenarios is underestimated. It is recommended that the results obtained for portions where field data are not available are examined in greater detail to ensure those are reasonable as well. It is also recommended to evaluate the estimation of congested travel times and the frequency of congestion to determine whether the discrepancies identified are related to a specific scenario or series of scenarios.
Once discrepancies are identified, appropriate modifications should be implemented.