Development of Analysis Methods Using Recent Data (2012) / Chapter Skim
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53 C h a p t e r 5 General Methodology One of the goals for this project was to explore the utility and usability of existing data in traffic safety analysis, specifically in the investigation of surrogate measures of safety. The approach requires vehicle trajectories.
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54 time envelope of small, accepted lag times during the crossmainline maneuver over the complete lifetime of the tracked vehicle. The search was separated by direction for the two cross-main-road maneuvers (one for each direction)
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55 evidence is not enough to pinpoint the source of the difficulty and certainly not enough to allow the creation of automated correction methodologies, which, in any case, are outside the scope of this project. The aforementioned issues constrained the project's ability to process large numbers of possible near crashes.
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56 Figure 5.3. Tracked target interface showing trajectories of a side-road vehicle.
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57 description of the event was deduced. Specifically, the sideroad vehicle is performing a northbound crossing of the intersection beginning from a standing position approximately 11 m (36 ft)
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58 cally, speed exhibits a single point drop of ~1.7 kph (1.0 mph) , which, apart from being physically unrealistic, is not evident in the distance measurements.
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59 -950 -850 -750 -650 -550 -450 -350 -250 -150 -50 50 150 -14 -12 -10 -8 -6 -4 -2 2 0 Time in sec feet 0 10 20 30 40 50 60 70 80 90 100 feet/sec Distance in feet Speed in feet/sec Figure 5.7. Mainline vehicle distance and speed.
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60 Exploratory modeling for both vehicles was conducted empirically in Excel to identify a plausible piecewise acceleration model. For the mainline vehicle, a three-stage model was fit, where a gentle deceleration lasting for about 3 s was followed by a stronger deceleration for 1 s and then by an even stronger one until the vehicle passed the conflict point.
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61 -90 -40 10 60 110 160 210 260 -12 -10 -8 -6 -4 -2 0 42 6 8 Time in sec feet Distance Figure 5.10. Side-road vehicle distance.
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62 -50 -40 -30 -20 -10 0 10 20 30 40 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 Time in sec feet Distance provided Distance modeled corrected prior to fitting Figure 5.11. Measured and modeled side-road vehicle distances.
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From page 63... ...
63 of the video data was conducted manually; issues concerning automatic reduction of video data, although important, were treated as outside the scope of this project. The main objective of the work described in Chapter 5 was to assess the ability of an alternative technology, based on using Doppler shift methods, to support the analytic approach.
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