Lane encroachment

Due to the fact that the crash-near crash data were not available at the time this study was conducted, a surrogate measure was utilized. While time to collision is one of the most widely used surrogates, it was not able to be utilized in this study with the NDS data in its current form. Lane deviation has been used as a crash surrogate for both road departure crashes and crashes due to distraction (Donmez et al. 2006). Previous studies have often used lateral placement or encroachment to evaluate rumble strips (Porter et al 2004, Hallmark et al 2011 and Taylor et al 2002).

Lane deviation was provided in the DAS time series data as offset from the lane center. Other metrics such as distance from the left or right lane line could also be calculated using additional lane position variables such as lane width. However there were a number of issues that limited the number of traces where lane position was viable throughout the entire curve. This was due to noise being present in the data, which is expected with data collection efforts of this scale as well as due to the machine visioning algorithm in the DAS. It depends on lane lines or

differences in contrast between the roadway edge and shoulder in order to establish position so when discontinuities (such as breaks in the lines due to intersection or lane lines being obscured) in lane lines occur, offset is reported with less accuracy. As a result, lane offset could not be reliably used as a surrogate and therefor it was determined that encroachments, or a lane line crossing would be used instead.

For the likelihood prediction model “encroachment” was used as the dependent variable. A

right-side encroachment was defined as the right side of the vehicle crossing the right edge line (when present) or the estimated boundary between the lane and shoulder (when lane lines were not present). A left-side encroachment is defined as the left side of the vehicle crossing the centerline. In all cases, the centerline was visible. An encroachment was determined to have occurred when at least two of the following criteria were present:

 Vehicle edge is 0.2 meters beyond edge line/centerline/lane–shoulder boundary

 >= 0.2 g lateral acceleration is present

 Edge line/centerline/lane–shoulder boundary crossing is visually confirmed using the forward view.

These right and left-side encroachments were then redefined into inside encroachments and outside encroachments. An inside encroachment was when the encroachment was towards the inside of the curve. Therefore for right-handed (inside) curves it would be a right-side encroachment and for left-handed (outside) curves it would a left-side encroachment. For outside encroachments, the opposite was true.

4.2.3.4 Driver

The age of the driver at the time of the trip as well as the driver’s sex was provided along

including approximate glance location as well as any visual distraction. These kinematic data were reduced at the VTTI secure data enclave using a tool they developed which allowed for the analyst to code the glance location and distractions while viewing the various camera views simultaneously.

Driver attention was measured by the location where a driver was focused for each sampling interval. Scan position, or eye movement, has been used by several researchers to gather and process information about how drivers negotiate curves (Shinar 1977). The majority of studies have used simulators to collect eye tracking information. Because eye tracking is not possible with NDS data, glance location was used as a proxy.

Glance locations, shown in Figure 4.1, represent practical areas of glance locations for manual eye glance data reduction. Note that Figure 4.1 does not show “over the shoulder”, “missing”, and “other” eye glance locations. “Missing” was used when a driver’s face was

obscured due to glare or when a glance was not able to be determined. These were determined based on the University of Iowa team members’ extensive eye glance reduction experience. Glance locations were coded using the camera view of the driver’s face, with a focus on eye

movements, but taking into consideration head tilt when necessary.

Potential distractions were determined by examining both the view of the driver’s face and the view over the driver’s right shoulder, which showed hands on/off the steering wheel.

Distractions were identified when drivers took their eyes off the forward roadway. Potential distractions included the following:

 Route planning (locating, viewing, or operating)

 Moving or dropped object in vehicle

 IPod/MP3 (locating, viewing, operating)  Personal hygiene  Passenger  Animal/insect in vehicle  In-vehicle controls  Drinking/eating  Smoking

Figure 4.1 Glance Locations

Glance location and distractions were coded for each trace. The data reductionist indicated each time the glance location changed, and the data reduction tool recorded the time stamp. Similarly, the start and end times for distractions were also recorded.

Glance location was further reduced to indicate time spent in “eyes-off-roadway” while

engaged in roadway-related tasks or “eyes-off-roadway” engaged in non-roadway-related tasks based on data coding used by Angell et al. (2006). Roadway-related glances or situation

awareness (SA) included glances to the left mirror, steering wheel, and rear-view mirror. Angell et al (2006) included glances to the right mirror. However, glances to the right mirror are not likely to be as common because drivers are not expecting vehicles to the right and it was difficult to distinguish glances to the right mirror from other right locations. Consequently, all glances to the right were considered to be non-roadway-related.

Glances to other locations are defined as non-roadway-related (NR). Additionally, when glances to roadway-related locations were also associated with a distraction, it was determined that these glances were likely to be non-roadway-related and were coded as such. For instance, a driver who was texting and glancing at the steering wheel was likely to be looking at a cell phone being held on or near the steering wheel rather than at the speedometer.

The drivers glance location and the presence of a distraction at 100 m upstream and at the CC were coded for use in the study. Additionally it was coded if the driver was distracted or had a non-roadway related glace at any time in the 100 m upstream or in the curve.