Overview
The second Strategic Highway Research Program (SHRP 2) addresses the challenges of moving people and goods efficiently and safely on the nation’s highways. In its Reliability focus area, the research emphasizes improving the reliability of highway travel time by reducing the frequencies and effects of events that cause travel time to fluctuate in an unpredictable manner.
Washington State Department of Transportation (WSDOT), in association with the Smart Transportation Applications and Research Laboratory (STAR Lab) at the University of Washington (UW), is one of the four research teams for conducting the pilot testing of Project L38. This research project mainly tested and evaluated SHRP 2 Reliability Data and Analytical Products, specifically those produced by the SHRP 2 L02, L05, L07, L08, and C11 projects. These analytical tools are designed to use for travel time reliability measurement, monitoring, enhancement, and impact assessment:
- Travel Time Reliability Measurement and Monitoring
- L02: Establishing Monitoring Programs for Travel Time Reliability
- Travel Time Reliability Analysis and Project Impact Assessment
- L07: Evaluation of Costs and Effectiveness of Highway Design Features to Improve Travel Time Reliability
- L08: Incorporation of Nonrecurrent Congestion Factors into Highway Capacity Manual Methods
- C11: Development of Improved Economic Analysis Tools
- Project Prioritization
- C11: Development of Improved Economic Analysis Tools
- L05: Incorporating Reliability Performance Measures into the Transportation Planning and Programming Process
This research project has two major objectives:
- To provide feedback to SHRP 2 on the applicability and usefulness of the reliability products tested; and
- To assist agencies in moving reliability into their business practices through testing of the products developed by the five SHRP 2 Reliability projects.
To test the SHRP 2 Reliability Data and Analytical Products, the research team, also referred as the SHRP 2 L38D research team, employed a research procedure that consists of three major steps: a) data compilation, integration, and quality control; b) experiment design for testing different products by SHRP 2; and c) test results evaluation and suggestions for possible improvements. Through this research project, the L38D research team followed this procedure closely in completing the research tasks. Specifically, the research team completed the following tasks for the reliability projects listed for testing:
SHRP 2 L02: The L02 travel time reliability monitoring procedure was evaluated using data collected from Washington freeways. To ensure the reliability of the tests, traffic detector data were processed for quality control. The data quality control method developed by the UW STAR Lab was used to identify erroneous data and correct the data whenever possible. This data quality control approach is general and fills in an important gap in the L02 procedure. Additionally, the data quality control procedure for travel time calculation used by WSDOT in the Gray Notebook was applied. Furthermore, to integrate the L02 product into WSDOT practice, the Travel Time Reliability Monitoring System (TTRMS) from L02 was implemented for monitoring the Puget Sound area freeway network travel time reliability on the WSDOT data analytics system - Digital Roadway Interactive Visualization and Evaluation Network (DRIVE Net). A new approach to calculate travel time from real-time loop data for long saturated facilities was developed and validated. Using the DRIVE Net tool, the travel time reliabilities for the I-5 and I-405 facilities from Lynnwood to Tukwila (approximately 30 miles long for each facility) were compared as a case study using the L02 methodology. Additionally, travel time reliability on a segment of I-405 was evaluated before and after a roadway improvement to measure the project’s effectiveness in improving travel time reliability. The L02 methodology was then extended to several other routes in the Puget Sound region to enable broad reliability analysis for WSDOT via the DRIVE Net platform.
SHRP 2 L05: The research team studied the L05 products carefully and confirmed the value of L05 products. WSDOT plans to test the SHRP 2 L05 tool together with WSDOT’s recently started SHRP 2 L01/L06 project. A test plan has been developed and introduced. A list of preliminary suggestions for L05 was summarized.
SHRP 2 L07: Various traffic data have been compiled for testing L07, which include WSDOT DRIVE Net Gray Notebook capacity analysis, single-loop detector data, roadway geometrics, treatments of construction projects on travel time reliability, traffic incident data, etc. The research team evaluated the tool by studying the cost-effectiveness of geometric design treatments in reducing non-recurrent congestion. A set of guidance for using the tool was developed. A median barrier construction project on northbound I-5 in Marysville was applied to test the L07 tool. Additionally, three other 1-mile long segments on I-5 were employed to evaluate the L07 tool. Besides the simple input and output validation, usability of the tool was also examined. The test results suggest that the L07 tool tends to underestimate travel time under high traffic volumes and generate over-optimistic measure of effectiveness and travel time index curves. All test results together with a list of potential tool refinements were summarized.
SHRP 2 L08: Both the FREEVAL and STREETVAL software tools provided by the L08 project were carefully studied. The usability of the tools was evaluated using data collected from different study routes. For FREEVAL, tests were conducted to verify tool accuracy for two different study sites in Seattle, WA: an urban section of I-5 with a high ramp density, and a less urban section of I-405 with zero ramps. Travel times for each study site were calculated using speed data collected from dual loop detectors. The Gray Notebook procedure employed by WSDOT for many years was used to calculate segment level travel times from spot speeds. The comparisons between the predicted travel time distributions from FREEVAL and the ground truth travel times suggest that FREEVAL tends to be over-optimistic in its predictions of travel times. A second test comparing results between different seed days showed that the seed day does have an influence on the effect of the results. This suggests that multiple trial runs using several different seed days may be necessary in order to achieve confidence in the test results. In summary, based on the testing results, FREEVAL does provide a close estimation of the actual distribution on travel times which implies that the main sources and factors influencing travel time reliability have been accounted for by the tool. In order to assess the accuracy of the STREETVAL software, a test was performed on SR- 522, an urban arterial near Seattle, WA. Results from the test were obtained by comparing the predicted travel times generated from the tool to the actual travel times obtained from Automatic License Plate Readers(ALPRs). The results show that the tool tends to under-predict the dispersion level of the travel time distribution. The predicted travel time distribution is less dispersed than the actual travel time distribution from the ALPR data, although the tool can reasonably predict the mean travel time. The discrepancy in travel times suggests that some other factors (not accounted for) are influencing the travel times. All test results together with a list of potential tool refinements for FREEVAL and STREETVAL were summarized in this report.
SHRP 2 C11: C11 accounts for travel time reliability as well as reoccurring congestion. It requires minimal data for performing assessment of impacts of highway investments, and thus allows users to perform quick assessment on the effects of highway investments. The tool comes with simple and easy scenario management features. It facilitates analyses of multiple scenarios by allowing creating and saving new scenarios with relative ease. The tool was evaluated using traffic data collected from the I-5 facility through the Joint Base Lewis-McChord (JBLM), also known as the I5-JBLM project. Six alternatives were compared using the tool. A benefit-cost analysis was performed using benefits from the travel time reliability tool. The tool was also tested to assess if it needs any further improvements for enhancing its potential for use by transportation agencies. After extensive testing on different improvement options, the research team developed a set of recommendations for further improving the tool.
In summary, the SHRP 2 Reliability Project products are clearly in need to address the practical challenges in travel time reliability monitoring and analysis transportation agencies are facing. However, most tools require significant improvements to the application level. Details of the test data, test procedure, and test results are documented in this report.