This study sought to identify which braking strategies are more often used in a car-following task when only optical cues to deceleration are available (no brake lights). Previous research identified three braking strategies for stopping to a stationary obstruction: regulation (deceleration at a near-constant magnitude), slam-on-the-brakes (increasing magnitude of deceleration), and bang-bang (initial high deceleration followed by a less deceleration). We used a car-following task with braking profiles which included variable decelerations to examine which of these strategies is most often used when drivers are not presented with brake lights warning of the deceleration of the lead vehicle. Results showed that individuals tend to use the slam-on-thebrakes approach (soft-then-hard braking) more than regulated (constant braking) or a bang-bang approach (hard-then-soft braking) when following vehicles without brake lights. These data form an important baseline of behavior for evaluating the effects of brake lights and other deceleration displays on braking behavior.Rear-end collisions account for approximately 28% of vehicle crashes in the United States (Lee, McGehee, Brown, & Reyes, 2002). The cost of these collisions to society has led to a large body of research on the influence of a variety of optical cues and displays on braking and car-following behavior (see e.g.However, despite this large body of research, one area that has not yet been studied is how drivers respond to non-constant emergency decelerations of lead vehicles in a car-following task.Drivers rarely, if ever, decelerate at a constant rate. Rather, braking behaviors are dynamic depending on whether the driver has over-or under-estimated the brake pedal pressure needed to maintain a safe following distance and relative velocity of other vehicles and obstacles. Yilmaz and Warren (1995) identified three braking strategies used by drivers in simulations of braking to stop short of a stationary obstacle. Some drivers appeared to minimize approach time by using a slam-on-the-brakes control strategy where a zero or low initial deceleration is followed by a rapid increase to maximum deceleration. Other drivers used a bang-bang strategy which minimizes collision risk by initially overestimating the required deceleration and then letting off the brake to lower deceleration magnitude. A third regulated strategy was also identified in which moderate and frequent braking adjustments are made. This last strategy still does not maintain an exactly constant deceleration, though it comes closest. Using a similar obstacle approach task, Fajen (2005) found that optical variables such global optical flow rate (GOFR) and edge rate (ER) can affect the magnitudes of both initial braking and braking adjustments, and that drivers' braking strategies are influenced by an interaction between optical factors and control dynamics.Despite the evidence that braking behavior rarely exhibits constant deceleration, research has not yet addressed how drivers respond to non-constant...
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