Analysis of Naturalistic Driving Study Data: Offset Left-Turn Lanes (2014) / Chapter Skim
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12 C h a p t e r 3 Data used for the study included intersection characteristics from the Roadway Information Database (RID) , visual inspection of aerial and street-view images from Google Earth and ArcGIS maps, environmental characteristics during turning maneuvers of interest observed in NDS video files, NDS driver demographic data, and time-series data related to the trip from the in-vehicle data recorders.
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13 In Step 2, geographic information system (GIS) tools, in cluding ArcMap and Google Earth, were employed to evaluate basic intersection characteristics.
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14 Table 3.1. Intersections Used in Phase 1 Analysis Unique Object ID (VTTI)
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15 • There was no way to distinguish the minor and major routes at an intersection without looking at a map. • The RID provided a database of speed limit signs, but the speed limits could not be tied to intersection approaches.
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16 Step 3 In Step 3, the remaining intersections were reviewed in aerial and street-view maps to record the following information: • Presence of opposing single-lane left-turn lanes; • Direction of approaches of interest (north-south approaches, east-west approaches, or both) ; • Offset measurements; • Intersection skew; • Approach speed limits; • Number of legs (verification of CTRE database)
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17 • Intersections with more than two through lanes opposing the left turns of interest; and • Intersections where anything about the geometry or other characteristics would likely cause abnormal gap-acceptance behavior (e.g., significant grade, railroad tracks near the intersection)
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18 NDS drivers at the approaches that had at least 10 turning maneuvers made by at least five different drivers. Unfortunately, few of the intersections met these criteria, especially at stop-controlled intersections.
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19 • Number of vehicles queued in front of study vehicle in leftturn lane; • Signal indication when study vehicle joined queue; • Signal indication when study vehicle began turn; and • Light condition during left-turning maneuver (light, dark without overhead lighting, dark with overhead lighting)
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20 gaps rejected or accepted by left-turning vehicles at the intersection. Second, these vehicles are often not in a position to see the signal indication facing the left-turning vehicle of interest, so it can be difficult to know which gaps in opposing through traffic are being rejected by the left-turning vehicle and which are simply being observed by the left-turning vehicle while it waits at a red signal indication.
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21 Figure 3.5. Video data reduction user interface.
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22 It should be noted that few pedestrians were observed in any of the videos, so variables related to the presence of pedestrians were not included. In one instance, a crossing pedestrian caused a left-turning driver to slow during the turning maneuver and this was recorded as an avoidance maneuver.
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23 Table 3.2. Variables Recorded During Video Reduction Variable Definition/Options Video-Level Variables Video ID Automatically recorded when video is selected Intersection ID Automatically recorded from video folder name Light condition Drop-down list: light, dawn/dusk, dark with street lights, dark without street lights Weather condition Drop-down list: dry, rain, snow Arrives in queue Timestamp: recorded when vehicle reaches rear of queue or stop bar if no queue exists Number of vehicles in queue Drop-down list: integers 0–7 and "8 or more" Time when rear not visible Timestamp: recorded when reviewer can no longer discern through vehicles passing through the intersection in the rear-facing video No visibility in rear view Check box: checked if this condition applies Time light turns green Timestamp: if signal is red at NDS time of arrival in queue, recorded at time when signal turns green Final gap estimated long Check box: checked if this condition applies (no oncoming vehicles visible in field of view of driver)
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24 accepted by the NDS driver, the gap end time is the time at which the next opposing through vehicle can be seen entering the intersection in the rear camera view. • Vehicle position.
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25 determine when the turning vehicle is in a certain position. Timestamp data must be recorded at points that are fairly easy to identify in the video, such as at a stop bar, rather than at positions that are not physically marked but might be calculated in a fixed-camera study, such as the center of the intersection or the conflict point.
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26 • Timestamp associated with each row of data collected; • File ID; • Associated video ID; • Alcohol indicator; and • Lighting indicator. The research team did not use these variables in the analysis, since all relevant information for the analysis could be obtained from the video reduction.
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