Safety Prediction Methodology and Analysis Tool for Freeways and Interchanges (2021) / Chapter Skim
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Pages 372-384
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From page 372... ...
372 APPENDIX B: DATABASE ENHANCEMENT As described in Chapter 4, the data maintained by three state DOTs provide the foundation for the database used for model calibration. These data describe road inventory information for the state highway system in each state.
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373 This process is used to digitize cross sections and alignments. When applied to alignments, the engineer digitizes the horizontal alignment of a length of roadway and saves the file of digitized locations.
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374 Figure B-1. Example digitized alignment.
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375 Figure B-2. Example digitized segment.
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376 Processing Software Computer software was developed to process both the alignment and segment files. This processing included reading the kml file, diagnosing the pin placements, and computing the desired database variables.
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377 Zecef Yecef Xecef North Up East Prime Meridian Curve Analysis Tool The Curve Analysis tool is used to compute the geometry of each horizontal curve represented in an alignment file. The tool computes the radius, deflection angle, chord, length of curve on a specified segment, curve begin milepost, and curve end milepost.
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From page 378... ...
378 computed deflection angles were found to be within 5 percent of the reported deflection angles. Further inspection of the data indicates that the larger deviations in either range occurs when the photograph quality is poor or when the curve can be characterized as having a short length and small deflection angle.
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From page 379... ...
379 Segment Tool The Segment tool is used to diagnose the segment file and compute the desired database variables. It includes an extensive set of routines that check the completeness and logic of the pins placed in the segment file.
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380 TABLE B-1. Variables computed from segment file Category Variable Description Roadway inc_drop-add_lanes Number of lane drops or adds on seg.
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From page 381... ...
381 1 2 1 2 4% 86%96% 14% 0% 20% 40% 60% 80% 100% Percent of Segments Measured Number of Lanes Reported Number of Lanes y = 0.3097x + 10.707 R2 = 0.0561 0 5 10 15 20 25 30 35 40 0 5 10 15 20 25 30 Measured Lane Width (x)
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From page 382... ...
382 y = 0.1412x + 3.6289 R2 = 0.049 0 2 4 6 8 10 12 14 16 18 0 5 10 15 20 25 Measured Left Shoulder Width (x)
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From page 383... ...
383 y = 0.9799x + 18.189 R2 = 0.9677 0 500 1,000 1,500 2,000 2,500 3,000 0 1,000 2,000 3,000 4,000 Measured Curve Radius (x)
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From page 384... ...
384 y = 1.01x - 35.261 R2 = 0.9965 0 1,000 2,000 3,000 4,000 5,000 6,000 0 2,000 4,000 6,000 8,000 Measured Curve Radius (x)
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