Visual Attention and Driver Performance at Horizontal Curves

Despite the frequency with which drivers encounter curves on highways, curves are regularly identified as locations that experience disproportionately high crash rates. Crash data suggest that inattention is one of the leading causes of crashes at any location and on any facility. Traffic control devices (TCDs) can be installed at curves to provide drivers the information necessary for safe navigation. The research in this dissertation examines the theory that TCDs at curves are not only beneficial because they provide drivers information, but also because TCDs promote increased attention. With increased attention, drivers then navigate the curve more safely. A study of driver behavior was conducted to examine three hypotheses regarding the relationships between driver attention, navigational performance, and TCDs that are used at curves: 1) TCDs lead to improvements in operational performance at curves, 2) TCDs lead to increased attention in advance of curves, and 3) increased attention before curves leads to improved performance within the curve.

The driver-behavior study included the collection of eye-tracking and operations (speed and acceleration) data from unfamiliar drivers on a two-lane highway. Data were collected from over 100 study participants who each drove for approximately 1 hour. The hypotheses were tested using multivariable mixed models that identify relationships between the three components (TCDs, attention, and performance) while accounting for geometric and operational features at each curve. The principal findings from the study are that: 1) drivers operationally respond to TCDs by adopting a more-conservative behavior, 2) TCDs affect attention by influencing when drivers perceive relevant curve information, and 3) an earlier increase in cognition leads to a more-conservative navigation. Since TCDs influence where drivers perceive a curve, and the perception influences the operational performance, it is suggested that the selection of TCDs at curves can be based on the distance required for drivers to make a natural maneuver in advance of the curve in preparation for navigating it.