Feasibility of Using In-Vehicle Video Data to Explore How to Modify Driver Behavior That Causes Nonrecurring Congestion (2011) / Chapter Skim
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Pages 46-55
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From page 46... ...
. Empirical and Practical Measures FHWA recommended four travel time reliability measures: 90th or 95th percentile travel time, a buffer index (the buffer time that most travelers add to their average travel time as a percentage, calculated as the difference between the 95th percentile and average travel time divided by average travel time)
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From page 47... ...
The developed lognormal distribution was used to estimate segment and corridor travel time reliabilities. The reliability in this paper is defined as follows: A roadway segment is considered 100% reliable if its travel time is less than or equal to the travel time at the posted speed limit.
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The research suggested that the 90th percentile travel time is a meaningful way to combine the average travel time and its variability. The I-880 Field Experiment Analysis of Incident Data (11)
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Travel time variability in a noncongested state is primarily determined by individual driver preferences and the speed limit of the roadway segment. Alternatively, travel time for the congested state (recurring or nonrecurring)
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In particular, the mixture parameter λk in Equation 3 represents the probability that a particular travel time follows the kth component distribution, which corresponds to a particular traffic condition, as discussed earlier. This provides a mechanism for travel time reliability reporting.
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Home-to-work travel time histogram.The number of travel time observations for a given period depends on traffic conditions. Typically, the number of trips per unit time is larger for congested periods when compared with trips in a free-flow state.
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The multistate model provides a convenient travel time reliability analog to the well-accepted weather forecasting example. The general population is familiar with the two-step weather forecasting approach (e.g., "the probability of rain tomorrow is 80%, with an expected precipitation of 2 in.
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It not only reports the probability of encountering a congested state but also reports the expected travel time under that state.The multistate travel time reliability model is more flexible and provides superior fitting to travel time data compared with traditional single-mode models. The model provides a direct connection between the model parameters and the underlying traffic conditions.
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Monitoring and Predicting Freeway Travel Time Reliability: Using Width and Skew of Day-toDay Travel Time Distribution. Transportation Research Record: Journal of the Transportation Research Board, No.
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Guo. Calibration Issues for Multistate Model of Travel Time Reliability.
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