A determination study of velocity thresholds under night driving conditions was conducted and is based on the premise that the information available to the driver of the following car concerning the state of the lead car is primarily provided by the taillights of the lead car. When a relative velocity exists between the two cars, this visual information appears as a change in the visual angle subtended by the two taillights of the lead car and apparent changes in the brightness and area of the taillights. Car- following is defined as that phenomenon in which a vehicle follows a lead vehicle which is travelling at an arbitrary speed. Velocity threshold is defined as that relative velocity which the driver of the rear vehicle can detect with a 50 percent probability at a given headway for a given presentation time. The headway is taken as the distance from the drivers eyes to the rear bumper of the lead vehicle. For the presentation times of relative velocity used in this study, the changes in headway were so small that taillight brightness and area were taken as fixed, so that velocity thresholds were obtained by considering only the change in visual angle. Velocity thresholds for daytime driving were obtained in a previous study using an automobile simulator which was also used for the night velocity threshold test. The driver velocity threshold was determined as a function of headway and presentation time of the relative velocity. Two general velocity threshold equations were derived which interrelate the velocity threshold with the presentation time and headway for the simulated situation. Calculation of the positive and negative night velocity threshold is simple after the headway and presentation time are known. A comparison was made between day and night velocity threshold , both obtained from automobile simulator experiments with the result that the night velocity threshold is generally smaller than the corresponding day velocity threshold. This deviation is due to the modification of the environment. References' velocity thresholds in car-following, e.p.Todosiev, presented at 43rd annual meeting of the highway research board, 1964. (Author/Publisher)
Abstract