Nicole Oneyear

Evaluation of driving behavior on rural 2-lane curves using the SHRP 2 naturalistic driving study data

INTRODUCTION Over half of motor vehicle fatalities are roadway departures, with rural horizontal curves being of particular interest because they make up only a small share of the system mileage but have a crash rate that is significantly higher than tangent sections. However the interaction between the driver and roadway environment is not well understood, and, as a result, it is difficult to select appropriate countermeasures. METHOD In order to address this knowledge gap, data from the SHRP 2 naturalistic driving study were used to develop relationships between driver, roadway, and environmental characteristics and risk of a road departure on rural curves. The SHRP 2 NDS collected data from over 3,000 male and female volunteer passenger vehicle drivers, ages 16-98, during a three year period, with most drivers participating between one to two years. A Roadway Information Database was collected in parallel and contains detailed roadway data collected on more than 12,500 centerline miles of highways in and around the study sites. RESULTS Roadway data were reduced for rural 2-lane curves and included factors such as geometry, shoulder type, presence of rumble strips, etc. Environmental and traffic characteristics, such as time of day, ambient conditions, or whether the subject vehicle was following another vehicle, were reduced from the forward roadway video view. Driver characteristics, such as glance location and distraction were reduced from the driver and over the shoulder videos. CONCLUSIONS Logistic regression models were developed to assess the probability (odds) of a given type of encroachment based on driver, roadway, and environmental characteristics. At the point this study was undertaken, crashes and near crashes were not yet available and only around 1/3 of the full SHRP NDS dataset could be queried. As a result, the likelihood of crossing the right or left lane line (encroachments) and speeding were used as dependent variables.

Analysis of Naturalistic Driving Study Data: Roadway Departures on Rural Two-Lane Curves

Rural curves are known to pose a significant safety problem, but the interaction between the driver and roadway environment is not well understood. Thus, the objective of this research was to assess the relationship between driver behavior and characteristics, roadway factors, environmental factors, and the likelihood of roadway departures on rural two-lane curves. To accomplish this, data from the second Strategic Highway Research Program (SHRP 2) Naturalistic Driving Study (NDS) and Roadway Information Database (RID) were used to develop relationships between driver, roadway, and environmental characteristics and the risk of a roadway departure on curves. This research was tailored to address four fundamental research questions: What defines the curve area of influence? What defines normal behavior on curves? What is the relationship between driver distractions; other driver, roadway, and environmental characteristics; and risk of roadway departure? Can lane position at a particular state be predicted as a function of position in a prior state? Since four fundamental research questions were addressed, a different methodology was developed specific to each. In addition to the analytical method, the data sampling and segmentation approach, general variables considered, results, and implications are discussed for each question.

Identifying Curve Reaction Point Using NDS Data

The object of this research was to use naturalistic driving study data (NDS) to determine where drivers begin reacting to the presence of a curve. Understanding where drivers begin to react to the curve is important for optimal placement of traffic control devices, such as advance curve warning signs, as well as other countermeasures. Time series data were modeled using regression analysis. Results indicate that, depending on radius of curve, drivers begin reacting to the curve 164 to 180 meters (538.1 to 590.6 feet) upstream of the point of curvature. This was compared against sign placement guidelines in the 2009 Manual on Uniform Traffic Control Devices, and it was determined these guidelines are appropriately set based on where drivers actually react to the curve. The analysis found that drivers begin reacting to the curve sooner for curves with larger radii than for curves with smaller radii. Drivers may not be able to gauge the sharpness of the curve, or sight distance issues may be a concern for sharper curves. It should be noted that the model only identified where drivers reacted to the curve. This research question did not attempt to answer whether the reaction point was sufficient for drivers to successfully negotiate the curve. It is also noted that sample sizes are small. Due to resource and data constraints it was not possible to model a large number of drivers over large variation of different curve types. Consequently, the results provide useful information but should be used within the context of the study limitations.