Modelling network travel time reliability under stochastic demand

A technique is proposed for estimating the probability distribution of total network travel time, in the light of normal day-to-day variations in the travel demand matrix over a road traffic network. A solution method is proposed, based on a single run of a standard traffic assignment model, which operates in two stages. In stage one, moments of the total travel time distribution are computed by an analytic method, based on the multivariate moments of the link flow vector. In stage two, a flexible family of density functions is fitted to these moments. It is discussed how the resulting distribution may in practice be used to characterise unreliability. Illustrative numerical tests are reported on a simple network, where the method is seen to provide a means for identifying sensitive or vulnerable links, and for examining the impact on network reliability of changes to link capacities. Computational considerations for large networks, and directions for further research, are discussed

Probe vehicle performance measures for assessing travel time reliability

Travel time reliability reflects the degree to which the amount of time needed for a trip is predictable. Metrics that quantify travel time reliability are emerging as a fundamental part of assessing the performance of transportation networks. Many states and municipalities are starting to incorporate travel time reliability into their transportation assessments and planning processes. Probe vehicle data is a prevalent data source which can be utilized to compute many of these travel time reliability metrics. This study used probe vehicle data from INRIX to compute, compare, and apply travel time reliability metrics on interstate segments in Iowa. It also looked at the concept of utilizing composite travel time reliability metrics to more concisely but still comprehensively convey travel time reliability. Different travel time reliability metrics were gathered from past literature and current FHWA rulemaking. These reliability metrics were computed and outcomes from each were compared. From ten different metrics, three groups of similar metrics were identified: the standard deviation of segment travel time index (TTI), the 15th-85th percentile range of TTI, and the buffer time index. These metrics, along with the level of travel time reliability and peak hour travel time reliability metrics from the FHWA, were applied at a segment level to the interstate network in the Des Moines area as well as across Iowa. Choropleth maps and identification of the most unreliable segments in the network emerged as useful ways to assess travel time reliability. It was observed that each metric would identify different segments as being unreliable because the metrics were sensitive to different characteristics of the TTI distribution. To concisely and comprehensively convey multiple aspects of travel time reliability, a method was developed for creating composite travel time reliability metrics using different combinations of the three key metrics identified earlier. Composite metrics were compared with each other as well as with the original travel time reliability metrics using choropleth maps and route progression plots. A composite metric combining the standard deviation of TTI and the 15th-85th percentile range of TTI emerged as a feasible composite metric to apply to assess travel time reliability at scale

How Effective are Toll Roads in Improving Operational Performance?

The main focus of this research is to develop a systematic analytical framework and evaluate the effect of a toll road on region’s traffic using travel time and travel time reliability measures. The travel time data for the Triangle Expressway in Raleigh, North Carolina, United States was employed for the assessment process. The spatial and temporal variations in the travel time distributions on the toll road, parallel alternate route, and near-vicinity cross-streets were analyzed using various travel time reliability measures. The results indicate that the Triangle Expressway showed a positive trend in reliability over the years of its operation. The parallel route reliability decreased significantly during the analysis period, whereas the travel time reliability of cross-streets showed a consistent trend. The stabilization of travel time distributions and the reliability measures over different years of toll road operation are good indicators, suggesting that further reduction in performance measures may not be seen on the near vicinity corridors. The findings from link-level and corridor-level analysis may help with transportation system management, assessing the influence of travel demand patterns, and evaluating the effect of planned implementation of similar projects

Travel Time Reliability and Level of Service

Travel time reliability (TTR) is familiar to travelers, and its indices are useful measures of the quality of a freeway’s service. Technical groups such as highway agencies are more familiar with a freeway’s level of service (LOS), but the LOS does not capture the variability in travel time. Similar to Pu (2011) this thesis introduces a modified buffer index (BI) incorporating a median rather than average travel time as a new travel time reliability measure. Current research by the SHRP 2 L08 Project Team defines freeway reliability LOS by determining equivalent travel time index for similar travel speed ranges shown on page 8 in TABLE 2. It is anticipated that the new index will be able to provide an additional model for defining LOS using TTR as a service measure on freeway corridors. Data from the BlueTOAD (Bluetooth Travel-time Origination and Destination) devices, which utilize Bluetooth technology, was used to develop a methodology to determine a LOS of the highway facility with the use of the new TTR index and a section of the I-12 highway was used for this study. The Wilcoxon Signed Ranked test was used to assess whether the difference between the median values of the new and existing BIs at various speed ranges are significant. From the Wilcoxon Signed Ranked test the difference between the new and existing BI was found to be significant for speed ranges sr; sr ≥ 60mph, 50≤sr≤59, 45≤sr≤49, 40≤sr≤44, 35≤sr≤39, but not sr \u3c 35mph. However the BI was inconclusive in providing an accurate measure for defining LOS. This is due to the data showing an increasing linear upward trend from LOS A to LOS C but then starts decreasing linearly downwards from LOS D to LOS F. More analysis is needed at all the speed ranges and should be carried out on several segments along the I-12 corridor instead of one segment in order to obtain comprehensive results. Data, including volume data for an entire year is also needed to comprehensively analyse the LOS

Valuation of travel time reliability in passenger transport

Rietveld, P. [Promotor]Verhoef, E.T. [Promotor

Evaluating Arterial Congestion and Travel Time Reliability Performance

This thesis presents an investigation of arterial travel time and reliability. Specifically an examination of the proposed arterial travel time reliability performance measures detailed in Federal Highway Administration’s Notice of Proposed Rulemaking on national performance management measures are performed. These measures, including level of travel time reliability and peak hour travel time ratio, are computed and compared to those currently used to quantify congestion and travel time reliability. Within this process several commonly used data sources are evaluated to determine the effects of data quality and data source on performance measure evaluation. The newly created Urban Streets Reliability tool is also evaluated for its ability to estimate the effect of several proposed projects on the travel time reliability of a transportation network. In conclusion, this thesis found that the proposed travel time reliability performance measures show definite differences in estimates of facility reliability as compared with currently used performance measures such as travel time index and planning time index. A variation in the magnitude of this difference was also observed based on a rural vs. urban roadway setting. Finally, further areas of research involving the use of the Urban Streets Reliability tool to estimate the impact of reliability improvements on side streets and the transportation network as a whole are discussed

Bus travel time reliability analysis: A case study

The travel time reliability of buses has become increasingly important for public transit companies. In this study, a novel approach is proposed to evaluate and analyse the travel time reliability of bus services provided by TransLink in Queensland, Australia. In view of their stochastic features, the two components of travel time-dwell time and driving time-are represented by discrete distributed and normally distributed random variables respectively. Accordingly, the travel time could be described by Gaussian mixture models. Based on the proposed model, impact analysis shows that bus line reliability would increase by around 15% if onboard top-up for 'go cards' (electronic tickets) was not offered by TransLink. It was found that not providing this top-up method would not significantly harm the benefit of go card users, but it would substantially increase the total social benefit thanks to improved bus line reliability