Pilot Testing of SHRP 2 Reliability Data and Analytical Products: Washington (2014) / Chapter Skim
Currently Skimming:
Pages 79-115
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 79... ...
79 CHAPTER 7 Pilot Testing and Analysis an SHRP 2 L08 Product 7.1 Introduction SHRP 2 L08 develops methods on incorporating travel time reliability into the HCM's analytical procedures. A guide is developed to provide step-by-step processes for predicting travel time reliability for freeway and urban street facilities.
|
From page 80... ...
80 system, OS X 10.9. The specifications of the computers tested -- operating system, system type, and version of MS Office installed -- are listed in Table 7.1.
|
From page 81... ...
81 software was created with. Given that the vast majority of computers used today are Windows based, this incompatibility is not a major concern.
|
From page 82... ...
82 Figure 7.3. FREEVAL segment number selection.
|
From page 83... ...
83 Figure 7.4. FREEVAL ramp metering option selection.
|
From page 84... ...
84 Figure 7.5. FREEVAL demand multiplier.
|
From page 85... ...
85 shorter study section might suffice. More guidance on selecting the appropriate study period would be helpful.
|
From page 86... ...
86 Map data © 2014 Google Figure 7.6. Map of two study locations (pin located at Northgate Mall)
|
From page 87... ...
87 7.4.1 Test 1. I-405 Facility, Seattle (Mileposts 27–29)
|
From page 88... ...
88 Figure 7.7. Sample of dual-loop data on I-405.
|
From page 90... ...
90 Volume data were collected in a similar manner as those in Test 1 in order to satisfy the demand data requirements of FREEVAL. The incident data were predicted using the HERS model, and the default values were used for the demand profile values.
|
From page 93... ...
93 The only instructions given to the user for selecting the seed day are that the seed day should be included in the reliability reporting period and that it should be a day in which no special events, such as big sports games, are occurring. There is no indication that multiple runs should be completed using the demand data from several different seed days in order for a test to be reliable.
|
From page 94... ...
94 7.7.1 Step 1: Project Purpose Before beginning an analysis, it is recommended that the user has a clear idea of what is to be gained in doing such an analysis, namely what is the project purpose. There are many possible motivations for using STREETVAL, which are discussed in the literature.
|
From page 95... ...
95 7.7.1.1 Study Period It is recommended that the study period for a given project be a maximum of 6 hours, and no less than 1 full hour. The study period should be selected such that the first analysis period within the study period is uncongested.
|
From page 96... ...
96 Figure 7.14. Urban Streets Computational Engine (USCE)
|
From page 97... ...
97 Figure 7.16.
|
From page 98... ...
98 After coding in the necessary inputs, the scenarios are generated by clicking the "Start Calculations" button. The generation process will take several minutes to complete and will vary depending the number of scenarios being evaluated.
|
From page 99... ...
99 7.7.4 Step 4: Scenario Evaluation This is the start of the HCM methodology, and it consists of evaluating the scenarios that were previously generated. In order to evaluate each scenario, the scenario engine is used.
|
From page 100... ...
100 Travel time; Travel speed; Stopping rate; Through delay; and Total delay. The user can also select if they would like to see results of the entire facility or only a particular segment.
|
From page 101... ...
101 another data file for additional analyses. Figure 7.21 shows the outputted list of each scenario, its date and time, and its corresponding performance measure.
|
From page 102... ...
102 Figure 7.23. Malfunctioning button circled in red.
|
From page 103... ...
103 that receives the combined volumes of each of the smaller access. In most cases, where access point demand data are unavailable, a traffic count study is required, and this process is labor intensive and costly to an agency.
|
From page 104... ...
104 7.10 Performance Test for STREETVAL Test Site Location: In order to test the accuracy of this tool, a test was conducted on an urban arterial using real traffic data. The test location selected is a roughly 1-mile stretch of SR 522, an urban arterial located in Kenmore, Washington, just outside of Seattle.
|
From page 105... ...
105 requires demand data for each movement of each intersection, and the rich sensor infrastructure installed along the study site gave the researchers complete demand data only for the main SR 522 arterial and not the side streets. When the research team became aware of this problem members had one of two choices: (1)
|
From page 109... ...
109 (e) Figure 7.26 Camera-captured images of studied intersections: (a)
|
From page 110... ...
110 Figure 7.27. Traffic Counter software user interface.
|
From page 111... ...
111 otherwise, the results of the test might be skewed. In this case, the plans had not been modified since July 2012, well before the first day in the reliability reporting period.
|
From page 112... ...
112 selected study site (mileposts 7.21 to 8.15)
|
From page 113... ...
113 Figure 7.28. Ground truth data distribution of travel times.
|
From page 114... ...
114 probability range, and underpredict travel times for the higher probability range (0.9 and greater)
|
From page 115... ...
115 From the results presented, it is clear that there is a large disparity between the predicted reliability of STREETVAL and the actual reliability obtained from the ALPR data. There are many potential explanations for this disparity.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.