Development of Roundabout Crash Prediction Models and Methods (2019) / Chapter Skim
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Pages 42-52
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From page 42... ...
42 Data Collection Approach and Findings This chapter presents the approach to the data collection, including data sources, database development, data reduction procedures, and the final database attributes and characteristics from which the crash prediction models were developed. 4.1 Data Collection Approach The following describes the overarching data collection approach, including quality control and assurance as well as how roundabout sites were identified for the database.
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43 database were not influenced by interim or long-term activities like work zones or construction activities. 4.1.2 Identifying Roundabout Sites The Modern Roundabout database (in addition to roundabout inventories received from public agencies during the outreach conducted as part of the literature review)
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44 basis for creating the data collection plan. Table 4-2 summarizes the candidate variables (i.e., desired data attributes)
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45 Data Attribute Applicable SPFs – Design DecisionsA Applicable SPFs – Planning and Network ScreeningA Roadway Inventory Data Area Type (urban/suburban, rural) – 11,12,13,14 Opening DateB – 11,12,13,14 Ramp Terminal Intersection ("yes" or "no" per site)
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46 needed crash reports and AADT by approach and movement, while the intersection-level models needed a digital summary of the crash attributes and AADT by major and minor street approach. 4.3.2 Roadway Inventory Data Roadway inventory data were available to varying degrees from state and local agency roundabout inventories, previous roundabout research databases, and as-built plans.
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47 Therefore, this speed is not reached by a motorist if a conflicting vehicle is in the roundabout and the entering vehicle must slow or stop to yield the right-of-way. This is consistent with how NCHRP Report 672 defines entering vehicle speeds in the context of roundabout design.
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48 provided for how the measurements were taken. Most of the data attributes discussed in the Data Reduction Procedures Guide included figures to illustrate the written descriptions.
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49 7. Confirm opening years for roundabouts with unknown opening dates.
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50 (i.e., Florida, Wisconsin, and Washington) make up approximately 57% of the database.
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51 Table 4-5 summarizes descriptive statistics for the geometric measurements completed by the project team for various roundabout types. 4.5.2.4 Traffic Volume Characteristics Table 4-6 summarizes the overall traffic volume characteristics of sites in the final database, based on average AADTs at each site for each leg.
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From page 52... ...
52 Multilane sites generally have more crashes per year than do single-lane sites. The spread of crash frequencies is also greater for multilane sites, whereas 75% of all single-lane sites have an average crash frequency of approximately 2.0 crashes per year or less, compared to 75% of all multilane sites having 7.1 crashes per year or less.
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