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From page 22... ... 24 C H A P T E R 4 - P R O J E C T D A T A B A S E Project Database This chapter summarizes the data collected and assembled for predictive safety model development. The discussion addresses the following topics:  A description of the data collection process. Read the entire page →
From page 23... ... 25 Development of Database Dictionary The Database Dictionary lists variables in the Project 17-89 dataset and provides a descriptive variable name, format of the variable value, type of data (integers, characters, etc.) , method of measurement, dimensional units (when applicable) Read the entire page →
From page 24... ... 26 For each PTSU and BOS facility, a comparison facility was identified. The research team strove to select comparison facilities that were similar to study facilities in terms of the number of lanes, spacing and complexity of interchanges, role in freeway network (such as radial route versus beltway) Read the entire page →
From page 25... ... 27 Step 3 – Geo-locate Each Site The research team collected the majority of the project's geometric data from Google Earth. This provided the research team with a high degree of confidence in the values of the geometric variables. Read the entire page →
From page 26... ... 28 The representative 24-hour volume distributions were obtained using data from the permanent automatic traffic recording (ATR) station nearest to each site. Read the entire page →
From page 27... ... 29 point just before the interchange ramps shown near the top of the map. The northbound and southbound directions are both assumed to have a one-way AADT volume of 87,000 vehicles per day (veh/day) Read the entire page →
From page 28... ... 30 and used historical Google Streetview images to determine how the hours varied over the years. Generally, after initial implementation, the duration of shoulder use was increased during the peak period in the peak direction and/or the shoulder was also opened in the off-peak direction during a second peak period. Read the entire page →
From page 29... ... 31 Assembly of Crash Data This section describes how each state's crash data were processed into a consistent format. The following variables were assigned to each crash using information in the state's databases:  State  County (for Ohio only, where mileposts reset to zero at each county line) Read the entire page →
From page 30... ... 32 police officer's car at the time the report was filed. GDOT staff cleaned these data to remove crashes associated with ramps and crossroads. Read the entire page →
From page 31... ... 33  A milepost with a resolution of 1/10th of a mile  A reference distance/unit/direction/name (such as "700 ft w of wb off>kunia sb," meaning 700 feet west of the westbound off-ramp to Kunia southbound)  A latitude/longitude Hawaii DOT staff indicated that the milepost values are approximate, and the reference distance/unit/direction/name and the latitude/longitude are more reliable. Read the entire page →
From page 32... ... 34 the attributes. One of the crashes in each of these pairs was removed from the dataset, as it was assumed to be a duplicate pair. Read the entire page →
From page 33... ... 35  For those facilities that served as a comparison facility to a PTSU or BOS facility, the study period was desirably the same as that established for the nearby PTSU or BOS facility.  The study period should be at least 1 year in duration and desirably 5 years in duration. Read the entire page →
From page 34... ... 36 of study from the dataset if crashes where construction was present were believed to have occurred during short-term construction or maintenance activities. Police Reporting Thresholds In general, state laws do not require the police to file a report for all property-damage-only (PDO) Read the entire page →
From page 35... ... 37 with the PTSU database, and study sites on BOS and BOS comparison facilities were added to the database to increase the sample size and the range of values for key independent variables. Database Summary This section summarizes the data assembled for the purpose of estimating the predictive models. Read the entire page →
From page 36... ... 38 Table 10. Database sample size. Read the entire page →
From page 37... ... 39 Table 11. Summary geometric and traffic characteristics. Read the entire page →
From page 38... ... 40 Table 12. Summary of turnout characteristics. Read the entire page →
From page 39... ... 41 Table 13. Freeway segment data summary for PTSU facilities. Read the entire page →
From page 40... ... 42 segments (not speed-change lane sites) having an additional basic lane and a lane drop. Read the entire page →
From page 41... ... 43 Table 17 presents a summary of the key attributes of the ramp exit speed-change lanes on PTSU facilities. Table 18 presents a summary of the key attributes of the ramp exit speed-change lanes on comparison and supplemental facilities. Read the entire page →
From page 42... ... 44 entrance speed-change lane sites, the number of ramp exit speed-change lane sites was lower than initially anticipated because some off-ramps on PTSU facilities were preceded by a "speed-change lane" greater than 1,600 feet long. Consistent with the speed-change lane procedure in the HSM Supplement, such sites were classified as freeway segments (not speed-change lane sites) Read the entire page →
From page 43... ... 45 Table 20. Freeway segment barrier characteristics for comparison and supplemental facilities. Read the entire page →
From page 44... ... 46 Table 21. Ramp entrance speed-change lane site barrier and PTSU characteristics for PTSU facilities. Read the entire page →
From page 45... ... 47 basis (not weighted to the length of the sites) Read the entire page →
From page 46... ... 48 Crash Characteristics The crash data for the study sites are summarized in Table 25. As shown in the bottom row of the table, the sites are collectively associated with 4,807 fatal-and-injury (FI) Read the entire page →
From page 47... ... 49 Speed-change-lane-related crashes were identified as those crashes that occurred: (a) between the painted gore point and the end of taper and (b) Read the entire page →
From page 48... ... 50 Table 27. Summary of crash rates for various PTSU features. Read the entire page →
From page 49... ... 51 Table 28. Proportion of each hour PTSU operation is open, except GA 400. Read the entire page →
From page 50... ... 52 Table 29. Proportion of each hour PTSU operation is open, GA 400. Read the entire page →
From page 51... ... 53 Table 30. Proportion of a typical day PTSU facility is open. Read the entire page →
From page 52... ... 54 Table 31. Examination of FI crash rate ratios associated with two conditions. Read the entire page →
From page 53... ... 55 The association between the "proportion of time during the average day that PTSU facility operates" and FI crash rate was examined using the data in Table 30 and Table 26. A length-weighted average "hours of operation" was computed for those facilities that operate at a different time period at various sections of their length. Read the entire page →

From page 22...

... 24 C H A P T E R 4 - P R O J E C T D A T A B A S E Project Database This chapter summarizes the data collected and assembled for predictive safety model development. The discussion addresses the following topics:  A description of the data collection process.