The quality of high-speed, high density traffic flow may be improved by use of an automatic system for the longitudinal control of vehicles in a traffic stream. The acceptable structures of such a system has been designed and is reportedly available for testing. (2) However, such a system must include a manual mode, so that a driver can, if necessary, quickly regain and keep control of his vehicle. Additionally, an in proved man-machine interface must be designed for non equipped vehicles, so that the performance of such vehicles approximates that of those equipped with an automatic system. One type of improved man-machine interface is discussed in this paper a type which may be used in both equipped and non equipped vehicles. A number of investigations, both under simulated and test track conditions, have shown that the headway in steady-state-car following is not invariant. For example, Bierly (3) found that under test rack conditions and constant lead car speed, the driver of a following car was unable to maintain a constant headway. In a study of simulated car following, Todosiev (4) found that headway. varied in an periodic manner about an average value. Since such unstable spacing between vehicles tends to affect efficient traffic flow, it is desirable to overcome or reduce such instability. Michael (5) has hypothesized that in steady state car following the driver of the following vehicle detects relative motion of the two vehicles indirectly by inference--i.e., by the detection of changes in headway. If this statement is valid, it means that the driver would be unable to maintain an invariant headway; for, given a small relative velocity between two vehicles, distance separation must increase by a "just noticeable difference" before he would detect any change. Hence, it would appear that the finite time required for a driver to detect slow relative motion of a lead vehicle is a main factor causing erratic headway control might in steady-state car following. Thus, it would seem that headway control might be improved by decreasing the drivers effective detection time. This Same conclusion was reached by Bierly (3) in a study of extravehicular spacing displays. He found that by giving the driver of the following vehicle a velocity-aided spacing visual display, bot the driver detection time and headway variability were reduced. His tests were conducted on a test track and vehicles wit conventional controls were used.
Abstract