The Influence of Forward Vision and Target Size on Apparent Inter-Vehicular Spacing

When one car follows another, the driver of the following car makes spacing judgments based on observing the lead ear within his field of vision. This visual field depends on a variety of design features of the following car, such as hood geometry, and is difficult to quantify simply. One quantity which relates to the driver visual field is the amount of roadway obscured from his view by his automobile. It is possible that the amount of this obscuration could influence spacing judgments. Furthermore, it is possible the size of the lead car, as characterized by the rear bumper length, might influence, spacing judgments. A laboratory experiment using color slides was devised to investigate if the amount of forward obscuration or target size influenced apparent spacing. The color slides showed the view of a driver seated in one car following another. Two different models of cars, with different values of forward obscuration and target size, served as lead and following cars. The influence of forward obscuration was also investigated by elevating the rear of one of the following cars. It was found that the lead ear target size did not systematically influence apparent spacing. On the other hand, changes in forward obscuration, whether caused by different following cars, or by elevating the rear of the same car, did influence apparent spacing; the same spacing appeared greater for smaller forward obscuration. These findings are related to reported test-track results.